Wasp Wednesday: Walden's Mason Wasp, Ancistrocerus waldenii

Guest post by Heather Holm

The Vespidae subfamily Eumeninae includes primarily solitary wasps that nest aboveground in pre-existing cavities (hollow stems or brambles, holes in wood) or in free-form mud nests. One morphological trait eumenines share with the social wasps also in the family Vespidae, is wings that fold longitudinally. Eumenines (potter and mason wasps) are generally black with white, rusty orange, and/or yellow markings. In the southeastern United States, some species have very prominent red markings and in some instances, these red markings replace the white or yellow markings of northern populations. Generally, eumenines hunt various families of moth larvae (caterpillars) although a minority prey on beetle larvae.

Potter and mason wasps use mud to line, partition, or construct their solitary nests. For those that nest in pre-existing cavities, partitioning the cavity with mud results in individual cells or rooms in which a single larva develops as it feeds on the cache of prey provided by their mother. Free-form mud nests are either single-celled (ex. potter wasps in the genus Eumenes) or contain multiple cells, comprised of multiple cells adjoining one another.

Video 1 caption: A female works the wet mud bolus with her mandibles to add an additional layer of mud to the edge of a partially completed cell.

For those mason or potter wasp species that construct free-form mud nests, a significant amount of time and energy is allocated toward water and soil collection to make mud. Mud is used to make one or multiple cells/enclosures that house a number of caterpillars, and eventually the developing wasp larva. To make mud, the wasp female first finds a water source, imbibes the water storing it in her crop, then searches for the perfect soil type to begin collecting soil particles. Each mason wasp can have their own unique soil preferences, some preferring sand, while others may seek out sandy loam soil. Perching on the ground, she scrapes and gathers a ball of soil particles in her mandibles and simultaneously regurgitates some water to form a mud bolus. When the bolus is sufficiently moistened and large enough, she carries it back to the nest held in her mandibles.

A female spends the night in a newly formed mud cylinder/cell. She’ll complete construction and provisioning of the cell the following day.

This month in my garden, I found a Walden's mason wasp female (Ancistrocerus waldenii) constructing a free-form mud nest on the side of a rock. This wasp species prefers to construct its nest attached to a hard surface such as a rock, concrete, or even on the side of a terra cotta flower pot! The rock in my garden that she selected has multiple concave indentations; these convenient divots helped form the back wall of the mud cells. After selecting the nest site, nest initiation begins with the construction of a single mud cylinder, and each layer of mud that forms the cylinder requires several mud-collection foraging trips. Once the cylinder-shaped cell is large enough to hold several moth caterpillars, the wasp female lays a single egg, suspended from the roof of the cell by a silken thread. Many solitary wasps lay their egg on one of the prey cached in the cell after they have fully provisioned the cell; eumenids, however, typically lay their egg in an empty cell prior to provisioning the cell with prey.

A closeup of an Ancistrocerus waldenii female peering out of an incomplete mud cylinder. This unfinished cell provides a convenient enclosure for her to spend the night, rest, or avoid inclement weather.

Providing food for her future developing larva comes next. She hunts for moth caterpillars on plant foliage, captures one, stings it to cause paralysis, then carries the caterpillar clutched beneath her. She fills the cylinder with multiple immobilized caterpillars, an average of nine, seals off the end of the cylindrical cell with mud, then begins the construction of the next, adjoining mud cylinder. Her egg, safely suspended from the roof of the cell, will hatch in the next few days and the tiny, first instar larva will drop onto the cache of caterpillars and begin feeding. The venom that paralyzed the caterpillars also keeps them alive for several days, long enough for the developing wasp to have a fresh and live supply of food while it develops.

An Ancistrocerus waldenii female returns to her nest with a bolus of mud held clasped in her mandibles. She is adding an additional layer of mud over multiple fully provisioned cells.

An Ancistrocerus waldenii nest can have multiple mud cylinders/cells, constructed adjoining or on top of one another. After all of the cylinders are complete and provisioned with prey, the female adds an additional thick layer of mud over the entire nest to help seal it off from predators and help prevent the nest from breaking down before the wasps inside emerge as adults.

Here are a few tips for identifying Ancistrocerus waldenii females although if you find a similarly-constructed mud nest attached to a hard surface, that will help narrow down your identification to a few species. Wasps in the genus Ancistrocerus have a prominent transverse carina [ridge] on the base of their first abdominal segment (T1, for tergum one, the first visible dorsal plate). Ancistrocerus waldenii has white (less often yellow) markings. The female has a spot on the top of the sixth abdominal segment (T6) and complete apical bands on the first through fifth abdominal segments (T1 to T5). The female also has entirely black antennae (many mason wasps have yellow or white markings on the underside their antennal scape [first long segment of the antenna, nearest face]).

Be sure to visit Pollination Press, LLC, Heather's publisher, and shop for her books. Her book on wasps is a fine complement to my own; and who doesn't need another guide to native bees? Thank you, Heather, for agreeing to do this guest post.

More Drama at the Bee Block

I was going to write at some point about how one of the other benefits of putting up a bee block ("bee condo") for solitary bees and wasps is that their parasites have a harder time finding them there than in a more natural situation. Well, last week I was proven completely wrong about that. On the positive side, I identified two new tenants in the block in our backyard.

Female mason bee, Heriades sp., on milkweed, before I had identified it

Early in the week I happened to see an insect fly from one of our blooming milkweed plants and literally make a bee line into one of the smaller holes in our bee block. I was not able to make an identification, so swiftly did it disappear.

Stakeout: female Sapygid wasp patiently eyeing potential hosts

Friday, June 24, I happened to glance at the bee block and noticed a very slender insect in one of the corners. I broke out the camera, took a couple pictures, and identified it as a sapygid wasp, family Sapygidae. Sapygids are parasitic on bees in the families Megachilidae and Apidae, and mason wasps in the family Vespidae, subfamily Eumeninae. The larvae of the sapygids either feed on the food stored for the host's offspring, or live as ectoparasites on the host larvae. Great.

Territorial dispute? Another sapygid joins the first one

Oh, here comes *another* sapygid. There were two on the nest block for only a brief time, and though it is not easy to separate the genders, I had no way of telling if it was a pair, or I believe they were two competing females. Males have even longer antennae and a blunter tip to the abdomen.

While photographing one of the sapygids, I got lucky. One of my pictures captured the mystery lodger in the bee block from earlier in the week.

Target detected: Sapygid wasp spies Heriades mason bee giving away its nest location

The insect coming to one of the smallest diameter holes is a type of mason bee in the genus Heriades. There are only eleven species of Heriades in North America north of Mexico, and five species in Colorado. Only Heriades cressoni has been officially recorded in El Paso County, but our bee block resident could still be one of the other species.

The female bee uses a pre-existing tunnel, such as an old beetle boring in a dead tree or log, or a hollow twig, in which to make her nest. She creates a series of cells with a partition of plant resin dividing one from another. She usually leaves one empty cell at the entrance before sealing the completed nest with a resin plug. Should a parasite break in, it might be duped into thinking the nest was empty; or at least dissuaded from having to break through a second "door."

Female Heriades sp. mason bee collecting pollen beneath her abdomen

The mother bee gathers pollen with a brush of hairs on the underside of her abdomen. Back at the nest she mixes the pollen with nectar she regurgitates from her crop (an internal food storage organ). This is "bee bread" that she fashions into a ball or "loaf" for each cell. She then lays an egg in the cell, and finally seals it with the resin partition. She repeats this scenario until the nest cavity is filled.

The sapygid wasp that had been waiting patiently for just the right moment to lay her own eggs in the bee nest finally made her move. She quickly backed halfway into the hole on the bee block and presumably deposited one or more eggs before fleeing the scene. This is the strategy that many, if not most, bee parasites use. They stake out a nest in the process of being provisioned, and enter when the host bee leaves to gather more nectar and pollen, or material used in making a partition between cells.

Game on! Female sapygid wasp laying eggs in Heriades mason bee nest

Another surprise happened when I saw a mason wasp approach and then enter another hole on the block. This one is different from the one I wrote about a couple weeks ago. It is smaller and more ornately patterned. It is either Parancistrocerus sp. or Stenodynerus sp. One cannot tell the two apart from images of live specimens in most cases. Even with actual specimens under a microscope it is difficult to make an identification. Like most cavity-nesting mason wasps, paralyzed caterpillars will serve as food for the larval offspring.

Female mason wasp, Parancistrocerus sp. or Stenodynerus sp.

I can hardly wait to see what comes next to our bee apartment building. Please comment if you yourself have a bee block (or more than one), and share what is coming and going from it, what parasites or predators you have seen lurking, and any other pertinent observations.

Sources: Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.
Scott, Virginia L., John S. Ascher, Terry Griswold, and César R. Nufio. 2011. "The Bees of Colorado (Hymenoptera: Apoidea: Anthophila)," Natural History Inventory of Colorado No. 23, University of Colorado Museum of Natural History, Boulder, Colorado. 112 pp.
Scott, Virginia. 2015. "Resin Plugs (part 1) and Their Bugs," The Bees' Needs Blog.

The Mason Wasp Euodynerus foraminatus Endorses Bee Blocks

Those "bee blocks," chunks of wood with holes of varying diameters drilled into them, are all the rage now for attracting solitary native bees like leafcutter bees and mason bees. They do work, no matter where you live, and I have proof. Ok, so the first occupant in our newly-hung bee block is actually a wasp, but that is also a good thing, and I'll explain why.

A bee block need not be as fancy as the one shown here. There are some standards you should adhere to, though, and a thorough explanation is found here. Solitary bees come in a variety of sizes, so having a good selection of various diameter holes is helpful.

Why am I excited that a solitary wasp is using our block? Wasps are "flower visitors" that go to flowers strictly for nectar to fuel their activities (think gas station, not grocery store), but they do a fair bit of pollinating in the process. The biggest benefit of wasps, though, is that they are parasitoids of insects we consider pests.

The scenario for the mason wasp using our nest box, Euodynerus foraminatus, goes like this: The female wasp catches and paralyzes a caterpillar, and flies it back to the nest hole where she stashes the victim, and usually several more, as a larder of food for a single larva offspring. She lays an egg on the first or last victim, and then erects a mud partition. She repeats the steps, such that one of those holes you drilled might end up filled with several cells, each holding numerous caterpillars that won't be eating your garden plants. The preferred prey of E. foraminatus are larvae of moths in the families Oecophoridae, Tortricidae, Gelechiidae, Pyralidae, Crambidae (subfamily Pyraustinae). All of these include some notorious pests, as well as caterpillars that conceal themselves in rolled or tied leaves that other wasps won't go to the trouble of extracting.

We know at least one nest tunnel is complete because it has been plugged with mud. You can identify the different types of bees and wasps using a "bee condo" by the kinds of closures they make. Some megachilids (mason and leafcutter bees) will make the final closure with a plug of chewed-up leaves. Other bees will plug a nest hole with plant resins.

Besides the comings and goings of the bee block inhabitants, you can get some other kinds of drama. While watching the bee block for signs of activity last Friday, I noticed a crab spider hanging out under the "eave" on our bee block. Sure enough, when the wasp approached the spider reacted, hanging of the roof and opening its "arms" in a potentially lethal embrace. The wasp ignored or never noticed the threat, but I ushered the spider to another part of our yard anyway.

You may think that there is no way one of these boxes would work in your yard. The above image is of our yard, behind our townhouse unit. Look at it! It is literally like ten-by-twelve feet. Surely, if we can make this work, so can you. It takes virtually nothing to put one up, and it offers both critical bee real estate for the insects, and hours of entertainment for you and your family. Since solitary bees and wasps do not have vast quantities of offspring and honey stores to defend, they are not going to sting you. Besides, they are too busy working.

Back to that mason wasp for a second. Euodynerus foraminatus is a very widespread species, found coast to coast in the United States, plus all Canadian provinces, and down into Mexico, too. There is a very good chance you could attract one to your own bee block.

Sources

: Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. "Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region," Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Stone, H.B. 2014. "Insects of the Week: Eumenids and Chrysidids," The Bees' Needs Blog.

How to (Almost) Catch a Leaf-tier Caterpillar (Video)

Last week I wrote about a mason wasp that successfully captured a leaf-rolling caterpillar. Amazingly, the day after I made that observation, I saw another species of mason wasp hunting a slightly different kind of caterpillar. This time it was a female Ancistrocerus campestris attempting of fish out a leaf-tier caterpillar (genus Psilocorsis, family Amphisbatidae) from its shelter between two lashed-together oak leaves.

The drama unfolded at Tully Lake, between Athol and Royalston in north-central Massachusetts, by the boat launch. I happened to notice the same schizophrenic behavior in this wasp that I had observed in the female Ancistrocerus unifasciatus female the previous day. I turned on the video feature of my camera a number of times, for long durations, but this wasp's attempts were ultimately unsuccessful.

Leaf-tiers, in contrast to leaf rollers, can involve more than one leaf, creating a "sandwich" like the one the wasp is exploring in the images and video here. I concluded, given the host plant (oak), that this was likely the work of a caterpillar in the genus Psilocorsis in the family Amphisbatidae. That information also helped me in my assessment of the wasp's identity.

Ancistrocerus campestris is of average size for a mason wasp. The forewing length of females ranges from 9-11 millimeters, and 6.5-9 mm for males. The color pattern on the abdomen is fairly consistent, the hind margins of the first three abdominal segments colored in yellow. The genus Ancistrocerus can be identified by a transverse ridge along the front surface of the first abdominal segment, creating an abrupt angle and "face" that faces the rear of the thorax. In other genera the abdomen slopes more gently toward the thorax.

This time, the wasp did try to tear into the leaf shelter, evidenced by the holes she chewed in the surface of the top leaf. The brown patch is likely the result of the caterpillar feeding on the bottom surface of that top leaf. The wasp also ran around the entire edge of the shelter, trying to wiggle inside and grab the occupant.

Had she succeeded, she would have flown her prize to her nest, inside a pre-existing beetle boring in wood, a hollowed-out sumac twig, or an abandoned mud dauber nest. She divides such tunnels into cells, after completing a single cell by laying an egg and then caching several paralyzed caterpillars. She uses mud to make partitions between cells, and for the plug that closes a finished nest. A nest may contain anywhere between two and eleven individual cells. This wasp has, on one occasion, been seen taking over active nests of the keyhole wasp Trypoxylon clarkei, kicking out the rightful owner.

Besides caterpillars in the family Amphisbatidae, this mason wasp uses caterpillars from the family Gelechiidae ("twirler moths").

Nests can be invaded by parasites including the bee fly Toxophora amphitea, and the tiny eulophid wasp Melittobia chalybii. Grubs of the wedge-shaped beetle Macrosiagon cruentum may prey on the wasp larvae.

Ancistrocerus campestris can be found from southern Ontario, Canada through New England south to Florida, and west to Minnesota, South Dakota, Kansas, and Texas. Look for this species along forest edges in woodland habitats.

Sources: Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. "Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region," Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Eiseman, Charley and Noah Charney. 2010. Tracks & Signs of Insects and Other Invertebrates. Mechanicsburg, Pennslvania: Stockpole Books. 582 pp.
Krombein, Karl V., Paul D. Hurd, Jr., David R. Smith, and B.D. Burks. 1979. Catalog of Hymenoptera in America North of Mexico Volume 2. Washington, DC: Smithsonian Institution Press. pp. 1199-2209.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.

How to Catch a Leafroller Caterpillar (Video)

Solitary wasps are amazing creatures, and their hunting behavior is particularly interesting. While my wife and I were in western Massachusetts last month, I was privileged to witness a female mason wasp, Ancistrocerus unifasciatus, successfully capture a leafroller caterpillar. I also got parts of the drama on video.

The scene: A large suburban residential backyard in Athol, Massachusetts, specifically planted to attract all manner of pollinating insects. Natural habitat is mixed hardwood and conifer forest, that abuts the property where this episode took place. Western Massachusetts is an odd mix of suburban and rural, actually, and it is difficult not to characterize this particular property as a "farm."

The leading actress: Ancistrocerus unifasciatus is a mid-sized mason wasp in the family Vespidae, subfamily Eumeninae. Females have a forewing length of 9.5-12 millimeters, males a forewing length of 6.5-9 mm. Both genders are basically deep brown or black with few yellow markings on the face, antennae, base of the abdomen, and legs. Males have a large yellow patch on the face, females a couple of spots.

Male, from Illinois. Note hooked antennae

Only females do hunting and nest building. The species ranges throughout the eastern U.S. west to Iowa, Kansas, and Texas. It also occurs in southern Ontario and Quebec, and Prince Edward Island.

The victim: I honestly cannot verify the identity of the caterpillar in this case, but it is certainly a leafroller in the moth family Tortricidae, and *possibly* the species Archips purpurana, which has goldenrod as a known host plant (among several others).

Is it coming out yet?

The wasp did not pursue its prey the way I thought she would. It even took me a minute to ascertain that she was hunting. I figured she would simply tear open the rolled leaf, grab the caterpillar, and go. Apparently the silk-bound fortress is more impregnable than I imagined.

Maybe at this end?

What the wasp did instead was pure genius. She took advantage of the caterpillar's instinct to "eject" when it feels like its home will be compromised. The wasp ran to one end of the leaf roll, then walked back, vibrating her abdomen to entice the moth larva to jetison itself. Back and forth she ran, as this video shows.

Unfortunately, I did not keep the camera running through the entirety of the hunt, partly due to fatigue, but when I saw the wasp suddenly had the caterpillar in her jaws, I resumed the video in time to see her fly to a nearby leaf to finish stinging her prey into paralysis.

Normally, the caterpillar, if threatened, takes a flying leap out of the leaf roll, trailing a silken line that it will then use to climb back once danger has passed. Kind of the caterpillar version of bungy jumping. The wasp obviously exploits this tendency, and very effectively.

Finishing off her victim with more stings

So, what does the wasp do with the caterpillar? Where does she take it? Adult wasps typically feed on flower nectar, aphid waste ("honeydew"), fermenting tree sap, and/or other liquids high in carbohydrates to fuel their energetic activities, like flying. So, this morsel of protein is not something the wasp would eat. The caterpillar is instead intended for her larval offspring.

And away she goes!

Ancistrocerus unifasciatus likes to set up house in abandoned mud dauber nests, especially those of Sceliphron caementarium and Trypoxylon politum. The mason wasp caches several paralyzed caterpillars in one of those cells. She lays an egg in the cell, then erects a partition and begins filling another cell along the length of the original, larger cell made by the mud dauber.

The larval wasp that hatches then has a larder of fresh food to feed it. Eventually it spins a silken cocoon, and pupates inside. An adult wasp emerges weeks later and chews through the mud wall to freedom.

Sources: Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. "Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region," Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Krombein, Karl V., Paul D. Hurd, Jr., David R. Smith, and B.D. Burks. 1979. Catalog of Hymenoptera in America North of Mexico Vol. 2. Washington, DC: Smithsonian Institution Press. 2209 pp.

Fossorial Mason Wasps, genus Pterocheilus

Solitary mason wasps in the family Vespidae, subfamily Eumeninae, are surprisingly diverse in appearance and habits. Most species nest in pre-existing tubular cavities, or make free-standing mud nests, but not all. Some excavate burrows in the soil. Perhaps the most accomplished digging species are members of the genus Pterocheilus.

Female Pterocheilus, Malibu, California

I so rarely encounter this genus, let alone a female actively digging a burrow, that when I came across one at Charmlee Wilderness Park in Malibu, California on May 19, 2011, I at first identified it as a beewolf, then another type of “sand wasp” before finally realizing it was a eumenid. The longitudinal folds in her wings when she was at rest easily betrayed her true identity.

Wasps that dig burrows are called “fossorial” by entomologists. Most of those wasps are equipped with stout spines on the front feet. This attribute is called the “tarsal rake,” and it is highly effective in moving sand and soft soil at a high rate of speed. Some wasps, rather than kicking soil will instead “pull” it out of the burrow by carrying a pile in their front legs and under their “chins,” while backing out of the tunnel.

Female Pterocheilus are equipped with a “beard” of long setae on their palps, segmented mouthparts behind the mandibles, which also have a fringe of hairs.

© Sarah Landry, in Evans & Eberhard, 1970

This modification of their anatomy, called a “psammophore,” allows them to carry a load of soil away from their nest location and scatter it into the landscape. This behavior effectively eliminates all trace of their activity, making it nearly impossible for parasitic insects to find the burrow once the entrance is sealed.

Female carrying soil in her "beard"

Pterocheilus quinquefasciatus is a fairly large wasp, females ranging from 13-16 millimeters in body length. This is the species I have found here in Colorado Springs. It occurs west of the Mississippi River to the Rocky Mountains, north to the Northwest Territories. It is also found in eastern Oregon and Washington, and southeast British Columbia. It is apparently absent from Arizona, Nevada, and California.

According to Jelle Devalez, in posts of this species to his Flickr.com photo stream, female wasps lay a single egg in the bottom of their burrow before they go hunting for caterpillars. Jelle discovered the species nesting in Badlands National Park in South Dakota. Apparently, caterpillars of the Darker Spotted Straw Moth, Heliothis phloxiphaga, are the preferred prey at that location. The female wasp paralyzes a victim, then carries it in flight to the burrow. Up to five caterpillars may be stored in one cell.

Female P. quinquefasciatus

Most species of Pterocheilus are not as large, or so widely distributed geographically, so are easily overlooked. There are roughly forty species in North America, with most of the diversity in the southwest U.S. Little is known about the biology of most species. P. texanus makes a shallow, vertical burrow terminating in a single subterranean cell, as do most Pterocheilus. Anywhere from 3-9 caterpillars are stored in each burrow before it is sealed (O’Neill, 2001).

As always, I encourage my readers to document their own observations of solitary wasps through still images, digital video, and note-taking. The sky is the limit for the scientific contributions you can make.

P. quinquefasciatus female

Sources: Bohart, Richard M. 1996. “North American Pterocheilus III. Subgenus Megapterocheilus (Hymenoptera, Eumenidae),” Insecta Mundi 10(1-4): 217-224.
Bohart, R.M. 1940. “A Revision of the North American Species of Pterocheilus and Notes on Related Genera (Hymenoptera, Vespidae),” Ann. Entomol. Soc. Am. 33(1): 162-208.
Devalez, Jelle. 2011. “Pterocheilus (Megapterocheilus) quinquefasciatus,” Flickr.com
Evans, Howard E. 1977. “Notes on the Nesting Behavior and Immature Stages of Two Species of Pterocheilus (Hymenoptera: Eumenidae),” J. Kans. Entomol. Soc. 50(3): 329-334.
Evans, Howard E. and Mary Jane West Eberhard. 1970. The Wasps. Ann Arbor: The University of Michigan Press. 265 pp.
O’Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 406 pp.

Wasp Wednesday: Pseudodynerus quadrisectus

The wasp known by the tongue-twisting name of Pseudodynerus quadrisectus is a handsome, conspicuous insect found over much of the eastern U.S. Since it has no common, English name, let’s learn the pronunciation of its Latin name: “Sue-doe-DIN-ner-us kwad-ri-SEK-tus.” There, that was easy.

All joking aside, this is an interesting mason wasp that is frequently confused at first glance with the Four-toothed Mason Wasp, Monobia quadridens. P. quadrisectus is slightly smaller, more slender in overall build, and features more white markings than its cousin. Both wasps utilize pre-existing cavities in wood as nesting sites, including the abandoned nests of the Eastern Carpenter Bee, Xylocopa virginica, in outdoor structural beams.

Females of this solitary species use mud to partition a tunnel into several cells, working from the bottom up. Observations indicate that the wasp cordons off an empty cell at the end of the shaft, using mud as a wall that serves also as the bottom of her first cell. Each cell is provisioned with paralyzed caterpillars, the size and quantity of which has not been adequately documented.

The mother wasp lays a single egg in the cell once it has been fully stocked, then creates another mud partition. This sequence is repeated until the wasp has filled the tunnel to her satisfaction. She closes the entire nest with another mud plug, leaving another empty cell between the last cell plug and the nest closure. This may serve as a decoy so that parasites breaking into the nest find an “empty room” instead of the expected wasp larva or egg.

There are apparently two generations of this species each year; the winter is passed in a dormant, pre-pupal larval stage (Krombein, 1967). Adult wasps are on the wing from around the first of June through the end of August or so. They feed on flower nectar to fuel their flight activity. The images here are of a specimen observed at the Hitchcock Nature Center in Honey Creek, Iowa on September 17, 2013.

The literature indicates that Pseudodynerus quadrisectus ranges from Florida north to New Jersey, eastern Pennsylvania, and northern Ohio; and west to eastern Texas, Kansas, and even Colorado. There are Bugguide.net data points for southeast Nebraska, and now southwest Iowa, so perhaps the species is expanding its range or we have only just now recognized its presence in some locations.

The predatory nature of this wasp makes it an ally in the battle against pests in your garden. You can attract them by planting summer- and fall-blooming wildflowers like goldenrod (Solidago spp.) and thoroughwort (Eupatorium spp.); and by providing lodging in the form of holes drilled in wooden blocks and hung under the eaves of your home or shed. Bundles of hollow twigs work well, too. Such “trap nests” are commercially available from a variety of sources, but logs and dead, standing trees are a natural resource for nesting wasps (and solitary bees, too).

Sources: Buck, M., Marshall, S.A., and Cheung, D.K.B. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp (PDF version).
Krombein, Karl V. 1967. Trap-Nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.

Wasp vs. Wasp

My wife and I went down to Fountain Creek Regional Park in Fountain, Colorado recently (the evening of June 2, 2013), and I happened upon an interesting scene. About five or six female mason wasps, Symmorphus sp., were nesting in beetle borings in a cottonwood log by the side of the trail. About four cuckoo wasps, Chrysis sp., were hanging out around the holes the wasps were using as nests. Heidi said I must have spent 45 minutes taking pictures of them all, but it was worth it because I got to observe what was happening.

The above image is one of only two really nice shots I got of the female Symmorphus mason wasps. They would alight near their nest hole, and dive in very quickly. If I approached too quickly with the camera, the wasp would fly off before entering. If I waited too long, I would get a shot of the wasp’s abdomen disappearing, or a seemingly empty hole. Waiting for the wasp to emerge was basically futile, as she would exit much more quickly than was possible to focus.

You have to have an appreciation of the size of the players and the beetle borings to know what I was up against. The borings are probably the exit holes of deathwatch beetles, family Anobiidae, which bore in dead, solid wood as larvae. The diameter of each hole is about the same as the end of a retracted ballpoint pen (about 3 millimeters). Yes, both the mason wasps and cuckoo wasps could fit through those holes.

”Science has strict rules against anthropomorphism, but if you ask me, those chrysidids were cunning and calculating.”

Meanwhile, the bright metallic green cuckoo wasps were not as easily disturbed as the mason wasps. They might run randomly around between holes, but most of the time they sat quietly in the vicinity of a group of holes. Science has strict rules against anthropomorphism, but if you ask me, those chrysidids were cunning and calculating. They were waiting for the wasps to show them which holes were active nests worthy of their attention.

Cuckoo wasps are parasitic in the nests of other solitary wasps. They can’t sting, but the last few segments of the abdomen of the female telescopes into an egg-laying organ that can reach into the bottom of one of those nest tunnels. The cuckoo wasp lays an egg in the nest of its host, and the larva that hatches generally consumes the meal intended for the host offspring.

In the case of Symmorphus, females catch and paralyze leaf beetle larvae that are free-living, or are leaf-miners (living between the layers of a leaf). At least one species of Symmorphus attacks leaf-mining moth caterpillars on occasion. The larval victims are packed into a cell along the length of the beetle boring, and the mother wasp lays her own egg on the last victim. She then creates a partition of mud or chewed wood fibers, and begins a new cell. The process is repeated such that several cells usually occupy one tunnel.

The mason wasps, for their part, were also quite cognizant of the cuckoo wasps. I witnessed at least one altercation whereby a female mason wasp fended off a too-eager chrysidid at the entrance to her nest. Cuckoo wasps, while they can’t sting, have a dense, pitted exoskeleton that effectively repels the bites and stings of their hosts. They can even roll into a ball as a last resort, becoming virtually impregnable.

Without collecting specimens of the wasps, which I did not do, I cannot conclude the species I was observing. Process of elimination narrows the possibilities to Symmorphus cristatus or S. canadensis for the mason wasps. The cuckoo wasps could represent one or more species in the Chrysis coerulans species group. Scientists are still trying to sort out how many species there actually are in that complex.

After getting up from my baseball catcher’s stance, I could feel how my legs had stiffened. The pain was worth the gain, though, and I encourage my readers to endure for the sake of personal and collective knowledge. Field observations are not the scientific priority they once were in the fledgling years of ethology (study of animal behavior). It could easily be you who makes history with a new host record for a predator or parasite, or records some other hitherto unknown association between species.

Sources: Bohart, R.M. and Lynn S. Kimsey. 1982. “A Synopsis of the Chrysididae in America North of Mexico,” Mem. Am. Entomol. Inst. 33: 1-266
Buck, M. Marshall, S.A., and Cheung, D.K.B. 2008. “Identification Atlas of the Vespidae (Hymenoptera: Aculeata) of the Northeastern Nearctic Region,” Canadian Journal of Arthropod Identification No. 5: 492 pp.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.

Wasp Wednesday: Four-toothed Mason Wasp

Black-and-white animals are always attention-getters, and that goes for insects, too. Among the more conspicuous of those is the “Four-toothed Mason Wasp,” Monobia quadridens. This member of the family Vespidae, subfamily Eumeninae, is commonly seen at flowers during the summer and fall over most of the eastern U.S.

The common name of Monobia quadridens is somewhat puzzling, and I am not at all certain that it is “official.” It has also been called the “Carpenter Wasp,” and simply “mason wasp.”

This species ranges from southern Ontario and the entire eastern U.S. west to Kansas, New Mexico, and Wisconsin. It is also recorded in northern Mexico. Another species, Monobia texana, exists in Arizona and Texas.

The adult wasps are most often seen on flowers like goldenrod and thoroughwort. Males are easily distinguished from females by the big white spot on their face (females have entirely black faces). When not sipping nectar, the females are looking for nesting sites or hunting for caterpillar prey.

These are solitary insects, and each female selects her own nest location. Much of the time they utilize abandoned tunnels originally bored by the Eastern Carpenter Bee, Xylocopa virginica. Check for such nests along the edge of the roof of your own home. Monobia quadridens has also been observed to evict mason bees (Osmia sp.) from wood borings, killing the bee eggs, larvae, and pupae in the process (Byers, 1972). Abandoned nests of the Black and Yellow Mud Dauber may also be used by M. quadridens. Rarely, the old burrows of ground-nesting bees are used.

Male M. quadridens on sumac flowers

Once she selects a suitable nest cavity, the female wasp goes about hunting for prey. Considering the large size of the wasp, the caterpillars it hunts are rather small: Primarily leafrollers like the Sweetgum Leafroller, Sciota uvinella (family Pyralidae, subfamily Phycitinae); the Dimorphic Macalla Moth, Epipaschia superatalis and Maple Webworm Moth, Pococera asperatella (Pyralidae: Epipaschiinae); the Grape Leaf-folder, Desmia funeralis (Crambidae: Pyraustinae); Schlaeger’s Fruitworm Moth, Antaeotricha schlaegeri (Elachistidae: Stenomatinae); Psilocorsis sp. (Amphisbatidae); Platynota spp. (Tortricidae); and unidentified caterpillars in the family Gelechiidae.

Each caterpillar is stung into paralysis and flown back to the nest. Several caterpillars are stuffed into the bottom of the nest tunnel, and a single egg laid there. The female then collects a mud ball which she fashions into a curtain that seals off that compartment. She will leave a small empty “room” between that cell and the next one along the length of the tunnel, repeating the process for as many cells she can comfortably create. Once filled, the nest tunnel is sealed with a final plug of mud. The empty rooms, called “intercalary cells,” are thought to confuse parasites into thinking that nobody is home.

So, the sequence in a given nest, from the bottom up is brood cell, intercalary cell (empty), brood cell, intercalary cell, and so on, with a final intercalary cell nearest to the nest closure. This last empty cell is called a “vestibular cell.” There are generally less than five brood cells per nest.

Each female wasp may create more than one nest, as long as she is physically able to do so. Inside the nest, each egg takes about two days to hatch. The larva then begins consuming its larder of caterpillars. It takes an average of 4-8 days to finish eating before preparing for pupation.

The wasp larvae do not spin cocoons, but do secrete some kind of “varnish” that they apply over the interior walls of their cells in the course of one to three days. Each larva enters the inactive pre-pupal stage about five days after it finishes feeding. About three days later, the larva pupates (in summer generations; it may overwinter as a pre-pupa later in the year). Ten to twenty-one days elapse before an adult wasp emerges (again, for the summer generation). Males take less time to metamorphose than females. The eclosed (emerged) adult wasp then lingers inside its nest cell for another 2-3 days while its exoskeleton hardens and it is able to chew its way through the mud partition(s) to freedom.

Not all make it, of course. Some orient themselves the wrong way during the pre-pupal stage and are not able to turn around inside their cells once they emerge as adults. Others are victimized by parasites. Mites (Tortonia quadridens and Monbiocarus quadridens), may take a toll, even though they are thought to be scavengers that feed on the remains of the caterpillar prey inside the cells. The larval stage of the bee fly Anthrax aterrimus feeds as an external parasite on the pre-pupal or pupal wasp. Larvae of Amobia erythrura, a “satellite fly” in the family Sarcophagidae, eat the caterpillars stored for the wasp larva, essentially starving it to death. Melittobia chalybii are tiny parasitic wasps in the family Eulophidae that lay their eggs in the larva of the host. This includes Monobia quadridens.

My good friend Joe Cohelo made a nice little video about these wasps. He includes some quality still images at the end. Much remains to be learned about this wasp despite previous studies, and your own observations, videos, and images could help increase our collective knowledge. Personally, I like the idea that these mason wasps can get to leaf-rolling pests even when chemical applications can’t easily penetrate the caterpillars’ refuges. It just goes to show that nature has its checks and balances, and sometimes we should let them operate on their own schedule.

Sources: Buck, Matthias, Stephen A. Marshall, and David K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).
Byers, George W. 1972. “Competitive Supersedure by Monobia quadridens in Nests of Osmia lignaria,” J Kans Entomol Soc 45(2): 235-238.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press. 570 pp.
Krombein, Karl V., et al. 1979. Catalog of Hymenoptera in America North of Mexico Vol.2 Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press. Pp. 1199-2209.

Wasp Wednesday: Euodynerus annulatus

Back on July 9, 2012, I visited the Florissant Fossil Beds National Monument in Teller County, Colorado. The area is well-known for amazing specimens of fossil insects, but the ones that live there now are pretty interesting, too. Take, for example, the mason wasp Euodynerus annulatus.

This species is widespread, found from coast to coast in the United States, south to Mexico; and in the Canadian provinces of British Columbia, Alberta, Saskatchewan, and Ontario (though the last record for Ontario was in 1954; and the record for Saskatchewan is very recent). There are five subspecies, three of them western in their distribution. The color and markings vary considerably among those different subspecies.

These are also fairly sizeable wasps, the length of the front wing varying from 8.5-10.5 millimeters. The species could be confused with the very common Euodynerus hidalgo, but the propodeum (hindmost segment of the thorax) is not as angulate in E. annulatus. The hind margins of the first and second dorsal abdominal segments (tergites) are also not clear and reflexed (turned up) as they are in E. hidalgo.

What surprised me the most about this wasp was learning that instead of using pre-existing cavities, or making mud nests, females of Euodynerus annulatus excavate burrows. Not only that, but they extend the tunnel aboveground as a curved mud “chimney.” Several individual cells branch from the main burrow underground. This wasp does not seem to be particular about the soil type, finding hard soil or soft soil perfectly suitable for its nest. The species does seem to favor situations close to water, as the female will regurgitate water to soften the soil during nest-building.

The chimney might help make the nest easier to defend from potential parasites, but it apparently serves as the source of mud pellets to make the final nest closure as well. Eventually, the turret is deconstructed entirely and the nest entrance made nearly invisible and flush with the surrounding soil (Rau and Rau, 1918).

The female wasps use caterpillars from the moth families Crambidae, Pyralidae, and Noctuidae as food for their larval offspring. The caterpillars are only weakly paralyzed (Rau and Rau describe some instances in which the larvae were still ambulatory), usually several placed in each cell. A single egg is suspended from a short thread attached to the wall of the cell before it is stocked with caterpillars. When all cells are provisioned, the nest entrance is sealed and the wasp leaves to begin a new nest.

Caterpillars of the genus Loxostege were recorded as a major host by Rau and Rau, and certainly the Alfalfa Webworm and its relations are exceedingly abundant here along the Front Range. Here’s what the adult moth looks like:

Male specimens of Euodynerus annulatus can be recognized by the hooked tips of the antennae, and their less robust appearance. I found both a male and female taking nectar from an early-blooming rabbitbrush plant (Ericameria sp.) at Florissant Fossil Beds.

Ironically, while no nest parasites are recorded for this mason wasp, the adult wasps are vulnerable to a type of insect called a “twisted-wing parasite,” Pseudoxenos hookeri. Parasitized wasps will have bulges in the abdomen, with what look like bullets wedged between abdominal segments. More on these bizarre animals in a future post.

I must thank Dr. Matthias Buck, Associate Curator of Invertebrate Zoology at the Royal Alberta Museum in Edmonton for identifying the wasps in these images, and describing a bit of their biology. I am hoping to get him down to Colorado at some point to see for himself the amazing diversity of Eumeninae to be found here.

Sources: Buck, Matthias, Stephen A. Marshall, and David K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp (PDF version).
Krombein, Karl V., et al. 1979. Catalog of Hymenoptera in America North of Mexico (volume 2 Apocrita (Aculeata). Washington, DC: Smithsonian Instititution Press. 2188 pp.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp. (Dover edition, 1970). Note that Euodynerus annulatus is described as Odynerus geminus on pages 300-312.