Wasp Wednesday: Another Cricket Hunter, Lyroda subita

Crickets in the family Gryllidae are sufficiently diverse, and abundant enough, to be the target hosts for a variety of parasitoid wasps, especially those in the families Sphecidae and Crabronidae. There are previous posts about the Steel Blue Cricket Hunter, and the genus Liris, but here in eastern Kansas there is another player. Lyroda subita is easily confused with Liris, but the clue is in the "toes."

Like all of the larger cricket-hunting wasps, Lyroda is solitary, each female constructing her own nest, in this case an underground burrow. Whether she digs it herself is the subject of debate. At least some observations indicate the wasps use the abandoned burrows of other solitary wasps rather than excavating a nest themselves. The tunnel of Lyroda subita can be fifteen to thirty centimeters below the surface of the ground. There may be only one cell, or two. Historical records are rather scant.

The female hunts almost exclusively crickets of the family Gryllidae, both adults and immatures (nymphs). She subdues her quarry with a paralyzing sting in a nerve center that renders the victim limp. Transporting such a bulky insect is no problem for the agile wasp. She slings it beneath herself, grasps the cricket's antennae in her mandibles, and away she goes. She can run over the ground with it, but can also glide or even fly with it. Multiple crickets are used to provision a single cell, after which she lays an egg on the last cricket, seals the cell, and then repeats the entire process.

There is at least one record of L. subita using a different host: a pygmy mole cricket of the family Tridactylidae. Since these are mostly subterranean orthopterans, and not that closely related to crickets, the how and why of this anomaly remains unanswered. Other species of Lyroda from other parts of the world are known to use pygmy grasshoppers, family Tetrigidae, as hosts, and those insects occupy similar micro-habitats as pygmy mole crickets. Maybe it is a matter of what is available in a given habitat, then. Pygmy mole crickets and pygmy grasshoppers occur mostly in wet or damp situations along stream banks.

In our Leavenworth, Kansas yard, there are large numbers of Gryllus field crickets, and ground crickets of the subfamily Nemobiinae, offering Lyroda plenty of options.

L. subita is a medium-sized insect. Females range from 10-13 millimeters in body length, males slightly smaller at 6-10 millimeters. Both sexes are slate gray in color with silver highlights, especially on the abdomen. In the right light it can appear the abdomen is banded in dark gray and white. The ocelli, a trio of simple eyes on the crown of the head, between the compound eyes, are present. The most easily observed feature is on each "foot." The last tarsal segment bears a very large pad called an arolium (plural arolia), which differs markedly from the petite feet of the nearly identical Liris genus. Liris also has only a single mid-ocellus, the lateral simple eyes being reduced to longitudinal scars.

This species occurs throughout most of the United States (except for Washington, Oregon and the southwest states), southern Canada, the northern half of Mexico, and also Cuba and Hispaniola. There are twenty-one other species of Lyroda, most of which are found in southeast Asia, plus Africa, Australia, and South America.

Sources: Kurczewski, Frank E., and Margery G. Spofford. 1985. "A New Host Family for Lyroda subita (Hymenoptera: Sphecidae)," The Great Lakes Entomologist 18(3): 113-114.
Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley: University of California Press. 695 pp.
Elliott, Lynette, et al. 2006. "Species Lyroda subita," Bugguide.net
Khvir, Viktor I., and Wojciech J. Pulawski. 2020. "A Revision of New World Lyroda Say, 1837 (Hymenoptera: Crabronidae)," Proceedings of the California Academy of Sciences Series 4, Volume 66, nol 13: 315-330.

Pipe Organ Mud Dauber, Trypoxylon politum, Found in Colorado

Yet another insect species appears to be expanding its range into eastern Colorado. I have recently discovered nests of the Pipe Organ Mud Dauber, Trypoxylon politum, at three locations in the vicinity of Colorado Springs.

This species is common throughout the eastern United States, but was previously known only as far west as Kansas and Nebraska. It is named for the multiple tubular mud columns that comprise its nest, and resemble the pipes on old-fashioned organs.

The nest from Fountain Creek Regional Park

Trypoxylon politum is not related to the familiar Black and Yellow Mud Dauber, or the Blue Mud Dauber, both of which are in the family Sphecidae. The Pipe Organ Mud Dauber is a member of the family Crabronidae, collectively known as "square-headed wasps." This is our only North American member of the "fabricator species group" of Trypoxylon that create free-standing mud nests. Most Trypoxylon species nest in pre-existing cavities such as nail holes, beetle borings in wood, and hollow stems or twigs.

Female working on the Bear Creek Nature Center nest

The first evidence I found of this species in Colorado was a pair of nests in the rafters of a large outdoor picnic shelter (ramada) in Bear Creek Regional Park near the foothills of the Front Range in Colorado Springs. That was on July 21, 2015, and I thought it might be a fluke. Maybe one wasp hitched a ride in a nest adhered to an object transported from an eastern state. That is still a likely scenario, but....

My wife then discovered a second nest on the inside wall of a wildlife viewing shelter in Fountain Creek Regional Park, on August 3. The park is located between the towns of Security/Widefield and Fountain, in El Paso County south of Colorado Springs. The longest column in this nest measured at least five inches. You cannot say these wasps lack ambition. One female created this entire nest.

The nest from Bear Creek Nature Center, August 13

Most recently I discovered a single-column nest on the exterior of the Bear Creek Nature Center, also located in Bear Creek Regional Park, Colorado Springs. That was yesterday, August 13. Well, it was a single-column nest. This morning, August 14, I discovered the female wasp completing a second tube. I managed to get a few grainy images and a couple nice videos, which I am sharing here.

Female bringing mud ball for second column in the Bear Creek Nature Center nest

A bit of architectural information. Each tube is partitioned on the inside into several individual "rooms," constructed individually from back to front inside the tube. The female wasp hunts spiders, especially orbweavers, paralyzing them and caching several per cell, laying an egg on the last victim before creating a mud partition and beginning the process again. She continues this until the column is filled.

The column itself resembles braided hair. One ball of mud, carried by the wasp up to the nest, is rolled into a thin half-arc. The next load is used to create the opposing, complimentary half-arc. Watch it happen in this video.

The female wasp works with astonishing speed. She could fly away and return to the nest with another ball of mud in about sixty seconds.

Sometimes, females work in tandem with a male. The male has a spine resembling a fishhook on the underside of the first abdominal segment. It helps anchor him in the nest when he is fending off enemies like parasitic wasps, flies, and other males of his species. The wasp here seemed to be working alone.

It will be interesting to see how well the Pipe Organ Mud Dauber succeeds here when we already have three species of mud daubers (including the new invasive species Sceliphron curvatum). They all coexist elsewhere, so maybe it will be the spiders that will suffer the most.

Green-eyed Wasps, Tachytes

Identifying wasps in the field is often problematic for a number of reasons. Wasps move quickly, and often you only get a glimpse. Mimicry complicates matters and you may actually be looking at a fly, moth, beetle, or true bug. "Field marks" are seldom visible, at least without a magnifying lens. One exception is the genus Tachytes, in the family Crabronidae. The larger species in the genus often have huge green eyes.

Tachytes from South Deerfield, Massachusetts

These insects have been referred to as "sand-loving wasps" in some literature, but they nest in a variety of soil types. I think they deserve the name "green-eyed wasps" because that character is more vivid, even if it does not apply to every species. Males in particular have very large eyes, the better to detect passing females or rival males while scanning the landscape from their perch on a stone, leaf, flower, or twig.

Male Tachytes defending territory from perch in Colorado

Interestingly, one of the hallmarks of the Larrini tribe within the Crabronidae is the reduction of their "simple eyes" (ocelli) to the point of being mere "scars." In Tachytes, the ocellar scars are shaped like golf clubs, having long "tails" running part way down the head. The image below shows the scars between the compound eyes, at the point where they begin to diverge from one another.

Close-up of Tachytes from Colorado

The female wasps excavate burrows in the ground, the tunnels ranging from 7 centimeters to nearly one meter in length, and to a depth of 7.5 to 70 centimeters. Several individual cells are arranged along the length of the burrow, or at the end of tunnels that branch from the main shaft. Some species dig their nests just inside the entrances of burrows made by other organisms such as rodents, lizards, or cicada killer wasps; and at least one species works at night.

All North American species provision those cells with immature grasshoppers (Acrididae), pygmy grasshoppers (Tetrigidae), katydid nymphs (Tettigoniidae), or pygmy mole "crickets" (Tridactylidae). The female wasp paralyzes the victim with her sting, then straddles it, grasps it by the antennae with her jaws, and flies it back to her nest. There, she deposits her prize in one of the cells. One to thirteen victims are placed in each cell, and an egg is laid on the last one.

Male Tachytes atop female in Colorado

Males employ two strategies to find mates. They emerge before females, so at first they defend small territories in the vicinity of areas where females are likely to emerge. Later in the season they defend territories around nesting sites. I have observed them defending territories around nectar resources, too, namely a solitary blooming saltcedar tree (Tamarix sp.) in a large expanse of degraded shortgrass prairie here in Colorado Springs.

The male pounces on the back of a female, pinning her wings to her body, and then beginning courtship behavior. Apparently this amounts primarily to waving his antennae frantically over the female's face, as shown in the short video below. This behavior may not hold true for all Tachytes species, and certainly the duration of courtship and copulation can vary dramatically.

Should the female be receptive, mating ensues. The image below clearly shows a male deploying his....um....ahem...."junk" in preparation for mating. Ok, the technical term is "aedeagus," composed of two "penis valves," and it is the blunt, central structure protruding from the tip of the abdomen in the image. The longer, more slender appendages framing the aedeagus are the "gonostyles." The "volsella" is a shorter spur at the base of each gonostyle. Insect genitalia are complex organs designed to work as a female "lock" and male "key" to prevent cross-breeding with similar species. Indeed, dissection of the male genitalia is often required for species identification in many insects.

Tachytes pair from Colorado

There are 35 species of Tachytes in North America north of Mexico. They are among our more common solitary wasps, easily observed as they feed on flower nectar, though they flit rapidly from blossom to blossom. Males also land on foliage, stones, or the ground, usually returning repeatedly to the same perch or one very close by. This represents the territorial defense behavior, and it allows for great photographic opportunities provided you don't make sudden movements. Happy wasp watching.

Sources: Bohart, Richard M. 1994. "A Key to the Genus Tachytes in America North of Mexico with Descriptions of Three New Species (Hymenoptera, Sphecidae, Larrinae)," Proc. Entomol. Soc. Wash. 96(2): 342-349.
Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Krombein, Karl V. and Paul D. Hurd, Jr. 1979. Catalog of Hymenoptera in America North of Mexico Vol. 2 Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press. pp. 1199-2209.
Kurczewski, Frank E. and Margery G. Spofford. 1986. "Observations on the Nesting Behaviors of Tachytes parvus Fox and T. obductus Fox (Hymenoptera: Sphecidae)," Proc. Entomol. Soc. Wash. 88(1): 13-24.
Kurczewski, Frank E. and Edmund J. Kurczewski. 1984. "Mating and Nesting Behavior of Tachytes intermedius (Viereck) (Hymenoptera: Sphecidae)," Proc. Entomol. Soc. Wash. 86(1): 176-184.
Kurczewski, Frank E. and Edmund J. Kurczewski. 1971. "Host Records for Some Species of Tachytes and Other Larrinae," J. Kansas Entomol. Soc.. 44(1): 131-136.
Kurczewski, Frank E. 1966. "Behavioral Notes on Two Species of Tachytes That Hunt Pygmy Mole Crickets (Hymenoptera: Sphecidae, Larrrinae)," J. Kansas Entomol. Soc. 39(1): 147-155.
O'Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca: Comstock Publishing Associates (Cornell University Press). 406 pp.

Sand Wasps, Genus Bembix

Solitary wasps are among the most easily observed of insects, and their behaviors and life histories are intensely captivating. Sand wasps in the genus Bembix are familiar and common throughout North America, digging their burrows in dunes, on beaches, and other habitats with loose, deep sand.

Bembix female, New Jersey

I had the good fortune of witnessing an industrious female sand wasp excavating her nest at Lathrop State Park in Huerfano County, Colorado last August 4, 2014. Insect activity was minimal in the late afternoon as the wind was picking up a bit and a thunderstorm was quickly approaching. While my wife was looking for a geocache, I studied the nearby vicinity and noticed a hole in the sand. Before I could complete the thought of "Hm-m-m, I wonder what dug that?," a sand wasp backed out of the cavity.

Bembix female, Lathrop State Park, Colorado

The industriousness of a Bembix female is something to behold, as you can see in the video below. She rapidly kicks out large quantities of sand using a "tarsal rake" of spines on each front leg.

There are twenty-one species of Bembix in North America north of Mexico, so generalizations about their behavior are risky. Still, the burrows are oblique, nearly horizontal in many cases, ranging from 19-57 centimeters in length, and a depth of 5-28 centimeters. The tunnels may curve, and usually end in a terminal cell. Several species also dig short, dead-end burrows or furrows in the immediate vicinity, probably to confuse parasites. The entrance of the real, finished burrow is thoroughly concealed.

The burrow is excavated before the wasp goes hunting. True flies in the order Diptera, exclusive of the suborder Nematocera, are used as prey. Bembix are generalist, opportunistic hunters. A victim is paralyzed or killed by the wasp's sting, and is then flown back to the nest. She uses subtle landmarks to unerringly find the buried entrance. Meanwhile, we can't remember where we parked our car. Most of our common Bembix species will lay an egg on this first victim, but some species lay an egg in the empty cell before commencing the hunt.

Once the egg hatches, the mother wasp brings flies to her larva as needed. This is called "progressive provisioning" and is more typical of parental care in birds or mammals than in insects. When the larva reaches maturity, the female wasp closes the cell. Inside, the larva spins an oblong cocoon, weaving sand grains into the structure and resulting in a hardened capsule. Overwintering takes place as a prepupa inside this cocoon, but there are usually two generations annually.

The mother sand wasp may fill in her burrow once her single larva reaches maturity, or she may construct one or two additional cells, each at the end of a short tunnel branching from the main burrow.

Bembix male, southern California

Male sand wasps are often seen alighting on the ground amid the numerous burrows of females, but they also participate in elaborate flight rituals called "sun dances." Males emerge before females, and fly at erratically at dizzying speed one or two inches above the ground attempting to detect virgin females about to erupt from their underground chambers.

Females join the males in flight if they are not pounced on immediately, and a pair that unites in mid-air will make a bee-line out of the mob and finish mating elsewhere before re-joining the masses. Should a pair tumble to the earth, great numbers of males will try and usurp the initial suitor.

Bembix female on saltcedar flowers, Colorado

Both sexes fuel their frenetic lifestyle with flower nectar, especially from composites (flowers in the aster family). Some of their mouthparts are fused into a tongue-like proboscis they use to probe for nectar. Sand wasps do nothing slowly it would appear, and one barely gets a glimpse of them, even at a flower, before the wasp is off to another destination.

Bembix wasps are plagued by the usual suspects that parasitize wasp nests: Cuckoo wasps (Chrysididae), velvet ants (wasps in the family Mutillidae), satellite flies (Sarcophagidae), and bee flies (Bombyliidae) being the chief villains in the sand wasp world. Additionally, the adult wasps can be victimized by parasitic thick-headed flies (Conopidae), or killed outright by robber flies (Asilidae).

Watching a nesting aggregation of sand wasps is never a disappointment, and at the very least you will find joy in each and every pesky fly they dispatch in providing for their larval offspring.

Bembix in Colorado

Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge, MA: Harvard University Press. 326 pp.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp. (Dover edition, 1970).

Aphid Killers: Pemphredon Wasps

Aphids are the insect equivalent of the wildebeest: they exist in vast numbers, and pretty much everything else eats them. Some other insects even specialize on aphids as prey. Chief among those are the "aphid wasps" in the genus Pemphredon, family Crabronidae (formerly a part of the family Sphecidae).

Not surprisingly, aphid wasps are not very large. Most are only ten millimeters in length if not smaller. They are solid black, and look a bit like a miniature thread-waisted wasp, the abdomen being on a short stalk (petiole) attached to the thorax. They have a cubical (square) head. These wasps are forever on the move, so it is very difficult to observe them, let alone get images.

The genus Pemphredon includes 20 recognized species in North America north of Mexico. Collectively, they range over most of the continent.

© Judy Jay in Bohart & Menke, 1976

Aphids are most abundant in spring and fall, so it is no surprise that Pemphredon are most commonly seen in May, then again in August and September. Pay attention to any aphid colony on a tree or weed, and eventually you will see these little wasps hunting. It is likely they also feed on aphids as adult wasps. Aphid wasps will visit flowers, but are only occasionally seen on blossoms.

Pemphredon are solitary wasps, each female making her own nest. She uses pre-existing cavities in wood, hollow stems, or she tunnels through the pith of broken twigs or berry canes. In fact, stems with thorns may be preferred because they are not likelyto be consumed by vertebrate herbivores.

I once spotted an uncharacteristically motionless Pemphredon on the side of a log. It was unmoved as I took images, until....a female made a hurried exit from a tunnel. Both wasps landed so close to me that I managed only one half-focused image of the pair, male on top, before they split. He had been waiting just outside her nest tunnel in hopes of mating with her. You can see her two antennae protruding from her hole, just in front of the male wasp in the above image.

The female wasp hunts aphids in their colonies, plucking them off stems and leaves with her jaws, stinging them into paralysis or simply crushing them, and then flying them back to her nest. She will stockpile ten to several dozen victims. One industrious female Pemphredon lethifer in England harvested 89 aphids for one cell! She will lay an egg after the last victim is gathered, but the egg may be placed at the back of the cell or halfway to the front.

Once she completes a cell, she then creates a partition, usually of chewed plant pith or sawdust, to close the cell, and create the bottom of the next cell. These partitions can be very thick, over 25 millimeters in some cases, perhaps the better to discourage parasites from digging through. She thus fills the tunnel from bottom to top, with as many cells as it will acoomodate. In situations where a twig is wide enough, some Pemphredon species will create branching tunnels instead of a single linear one.

Sometimes, the female wasp will guard the front of her completed nest to chase off potential parasites or competitors. Small carpenter bees (Ceratina spp.), compete for the same pithy-twig nesting sites as Pemphredon, and are not above destroying the wasp's nest to create their own living space.

Tiny cuckoo wasps (Omalus spp.) are parasites of Pemphredon nests, as are ichneumon wasps (Perithous mediator), bee flies (Anthrax irroratus), satellite flies (Senotainia trilineata), and other wasps and flies.

You can create housing for aphid wasps simply by drilling small diameter holes in a block of wood and hanging it off the ground under a protected place, like the eave of a garden shed. There are also ready-made lodges sold commercially for solitary bees that can be modified to suit the wasps, too.

Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Dollfuss, H. 1995. "A World Revision of Pemphredon Latrielle 1796 (Hymenoptera, Sphecidae)," Linzer biol. Beitr. 27(2): 905-1019.
O'Neill, Keven M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 406 pp.

Eastern Cicada Killer

Mowing the lawn one August day, Jim noticed saucer-sized piles of soil in the bare patches, with a large hole on the edge of each one. He figured it was the work of rodents until he saw an enormous wasp enter one of the holes dragging another large insect behind it. Jim decided to avoid that part of the yard.

This scenario, and others like it, plays out over much of the eastern United States during the summer, creating mystery, annoyance, or downright hysteria for those finding that the Eastern Cicada Killer, Sphecius speciosus, has taken up residence on their property.
A Community of Killers
Cicada killers are solitary. This means that each female wasp excavates her own nest. Many wasps may burrow in the same area, creating the impression that they are giant, social yellowjackets or hornets. Male cicada killers, while incapable of stinging, will drive off other males, other insects, even birds as they seek mating opportunities with females. They sit on the ground, or foliage, rocks, or other objects that give them a somewhat elevated perch from which to survey their territory. Watch them cock their heads alertly at the passing of other wasps.
The female digs her burrow before she starts hunting. The tunnel extends up to three feet, at a depth of two feet. Individual cells branch off near the end of this shaft. Each “room” will host one of her offspring.

The Eastern Cicada Killer hunts mostly “annual” or “dog-day” cicadas in the genus Tibicen. These large, loud insects are heard in the tops of deciduous trees during July and August. The female wasp flies into the canopy and combs each branch until she bumps into a cicada. She grabs the insect and stings it into paralysis. A “shrieking” cicada is likely being attacked by a cicada killer.
The Cicada Killer Life Cycle
Cicada killers are strong. A wasp may fly directly from the scene of the crime back to her burrow, carrying her prey beneath her. Sometimes the journey is accomplished in stages, gliding from the tree to the ground, up another vertical object to launch another short flight, and so on until she gets home. She has to hurry: birds often harass cicada killers into dropping their prey.
She dives down the entrance to her burrow, hauling her prize to one of the underground cells. One cicada is enough to grow a future male cicada killer, but a baby (larval) female cicada killer needs to eat at least two cicadas, sometimes three. The mother wasp lays a single egg on the last cicada put into a cell. When all cells are filled, she fills the nest entrance and leaves permanently.

Typical cicada used as prey The cicadas are paralyzed, not dead, which prevents them from spoiling until the wasp larva finishes consuming them. The egg hatches in a day or two, and the larva starts feeding. It matures quickly, in an average of ten days. The larva then spins a silken cocoon, incorporating soil particles into the capsule. Inside that covering it turns into a pupa, the externally inactive stage of metamorphosis. Pupae overwinter within their respective cells, the adult wasps chewing their way out the following summer and beginning the cycle anew.
Fueling up
Both male and female cicada killer wasps feed on substances rich in sugars and carbohydrates to fuel their energetic activities. Look for them on flowers where they sip nectar. Also look for them eating oozing, fermenting sap on the trunks of trees. Some of the images shown here depict this behavior. I even gently nudged one of the big female wasps into a better position while I was taking pictures.

Cicada killers are probably the largest, bulkiest wasps you are likely to see east of the Rocky Mountains from Massachusetts and southern Ontario to Florida and Texas. The adult wasps range from 30-40 millimeters in body length, though some females can be up to 50 millimeters (just shy of two inches). No wonder they can seem so intimidating.
Nothing to Fear
Solitary wasps will not sting unless physically molested, or you step on one in bare feet. Male wasps may behave aggressively, but they lack a stinger.

Should you be fortunate enough to have cicada killers in your garden, enjoy watching the drama of their lives. The adult wasps live only 2-6 weeks, so the phenomenon of their nesting is fleeting.
Sources: Holliday, Charles. 2012. “Biology of Cicada Killer Wasps,” Prof. Chuck Holliday’s www Page at Lafayette College.
O’Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, NY: Comstock Publishing Associates (Cornell University Press). 406 pp.
Shapiro, Leo, et al. 2012. “Sphecius speciosus: Eastern Cicada Killer,” Encyclopedia of Life.

Wasp Wednesday: The "Horse Guard"

Heidi and I were away last week in Cape May, New Jersey for a belated honeymoon, celebrating in the same place we had our first “date” back in October, 2010. We went a week earlier this time, and visited some locations we had missed on our last trip. Consequently, we saw some different birds and insects, including a wasp that was on my “bucket list.”

The Triangle Point Butterfly Garden, a tiny park near Cape May Point State Park, is planted with a variety of native and exotic flowers that attract many kinds of insects. We visited in the early afternoon of October 5, and found another party looking at the butterflies, but wondering what the big black and white wasps were.

”Oh, my God, that’s a Horse Guard!” I couldn’t contain my enthusiasm as I frantically focused my zoom lens on the wasp. I had forgotten that Stictia carolina, the largest of our “sand wasps” aside from cicada killers, ranged this far north, and persisted into the autumn months.

The Horse Guard is found from New Jersey and Pennsylvania south to Florida and west to Illinois, Kansas, and New Mexico (barely). It is most abundant in the southern Great Plains. Though solitary, each female excavating her own nest, many wasps may nest in a small area of sandy soil.

How did the Horse Guard get its name, you might ask? Also known as “cowfly tigers” and “insecto policia,” the wasps are specialist predators that chiefly attack horse flies. Naturally, the best place to hunt horse flies is around equines. The female wasps will fly around a horse, up and down each leg, searching for their prey. They can even fly backwards in front of a moving horse. This hunting behavior is frequently interpreted as aggression by “hornets” by the average, intimidated horseback rider or ranch hand. Once people understand the intent behind the wasps’ persistent hovering, the usual reaction is one of relief and elation.

”That’s fantastic! How can I encourage more of these wasps for horse fly control?”

Short of importing a sand dune, as the late Howard E. Evans writes in his book Wasp Farm, there is very little one can do to ensure the presence of horse guards at any given farm or ranch. The best thing to do is simply not kill them or accidentally obliterate their nesting areas.

Males search for females by engaging in “sun dances,” which are level flights in circles, figure eights, or sinuous patterns, occasionally perching on low herbs, dung, stones, or on the ground. These patrol beats are most often in the vicinity of female nesting areas, and usually in the morning hours. They will actively chase each other, or molest other large insects that pass through their individual territories.

Females take a surprisingly long time to complete a burrow, taking an average of 22-30 hours. Burrows are usually initiated in the morning, with frequent breaks as the sun becomes more intense, with digging activity increasing again in the late afternoon. The wasp closes the tunnel each time she leaves the vicinity. The burrow is a diagonal excavation, averaging 35-51 centimeters in length, and to a depth of 18-24 centimeters. Soil properties influence these numbers. The tunnel terminates in a single cell, where the wasp deposits a single egg.

Once the nest is completed, the wasp begins hunting, feeding her larval offspring in the progressive fashion that birds do. Between visits, the wasp makes both an inner closure that seals off the terminal cell, and an outer closure that obscures the nest entrance at the surface. Fifteen to thirty-five flies may be fed to the average wasp larva during its lifetime. Larger flies (like horse flies), mean fewer flies are necessary to feed a growing larva. Still, the hunting tactics of the wasps can be very effective in protecting livestock from blood-sucking flies.

The double closure of the burrow between the frequent visits by the mother wasp helps eliminate many of the opportunities parasites usually use to gain entry into sand wasp nests. “Satellite flies” in the family Sarcophagidae (subfamily Miltogramminae) do deposit their own tiny larvae on the prey carried into the nest by the female Horse Guard, but those larvae are generally content consuming the leftovers of prey, rather than attacking the wasp larva itself.

Interestingly, while I was employed by the Cincinnati Zoo in 1988, we received pupae of horse guards from Mississippi that yielded both the expected wasps, but also “Cow Killer” velvet ants, Dasymutilla occidentalis. This would imply that occasionally the Horse Guard offspring fall prey to larvae of velvet ants.

There are two other species of Stictia in the southern U.S., but even more in the New World tropics (28 species total).

Look for the Horse Guard if it ranges in your part of the U.S. All the specimens imaged here are females, by the way. Males, active much earlier in the season, have the white markings confined to the front half of the abdomen only.

Sources: Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World: A Generic Revision. Berkeley, California: University of California Press. 695 pp.
Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge, Massachusetts: Harvard University Press. 526 pp.
O’Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, New York: Comstock Publishing Associates (Cornell University Press). 406 pp.
Pulawski, Wojciech J. 2011. “Catalog of Sphecidae sensu lato,” California Academy of Sciences

Wasp Wednesday: Bembecinus

Once again, just last Saturday, July 28, I found myself baffled by a little wasp I found excavating a burrow in some sand not far from my home. I took images and, realizing that I didn’t recognize it, began the identification process. I started with something it reminded me of: a small Bicyrtes species. I then went up the classification ladder on Bugguide.net. How about the subtribe Bembecina? Not really, though Microbembex was close. Was it in the tribe Bembicini at least? Yes, that seemed like a safe bet. Browsing the images for the subtribes I found myself surprised that the Stizina looked promising. Indeed, it turns out I had been observing a female wasp in the genus Bembecinus.

The characters I found key to making the ID included the eyes, which are strongly convergent at the bottom of the face, and strongly divergent at the top of the head. The second submarginal cell in the front wing is petiolate or nearly so.

I thought I had lost my opportunity to photograph this wasp right off the bat. I made a quick move while she was down her burrow, but she popped back out quickly, saw me, and flew off. Luckily, she was determined to finish what she started, and returned shortly to continue digging. She would occasionally fly off, only to return a short time later, regardless of my presence or movements. At one point a tiny, curious ant walked into her burrow while she was inside it, and she literally kicked it out of her tunnel.

Good thing for the ant that female Bembecinus hunt leafhoppers (Cicadellidae and related families) as food for their larval offspring. Rather than stockpiling several prey and then leaving the larva to feed, Bembecinus practices an advanced form of parental care called “progressive provisioning.” She lays her egg in the empty cell at the end of her burrow, and then brings food to the larva on an as-needed basis. She can deliver, too. Researchers have recorded different species bringing in from 71 to 757 prey items to a single nest. One assumes the larger the prey species the fewer it takes to feed the wasp larva, but that is still a staggering amount of work for the mother wasp.

The burrow is eventually sealed permanently at, or before, the time the larva enters a pre-pupal stage. The female then begins the nesting process over again. Bembecinus is often highly gregarious, several to many individual females nesting in a small area. Indeed, I did find another specimen (though perhaps a different species) nesting nearby the first.

Interestingly, males of some species of Bembecinus actively dig to reach pre-emergent, virgin females. These males have short “tarsal rakes” of spines on their front feet, so may be mistaken for females themselves. They are among the most competitive of wasps when it comes to mating, and males may physically fight over a female at any point, including when another male is already coupled with a female.

Both genders gather in “sleeping clusters,” sizeable balls of wasps situated on twigs, stems, or foliage of plants near the nesting area. The clusters can be all males early in the season, and all females late in the season, though this varies with the species and maybe even the geographic area.

Bembecinus is not immune to nest parasites. Velvet ants (family Mutillidae), and cuckoo wasps (Chrysididae) have been recorded as parasites for different species of Bembecinus around the globe. Surprisingly, no fly parasites have been documented. Satellite flies in the family Sarcophagidae are insidious pests of most all other burrowing wasps, so this is a mystery.

There are currently ten species of Bembecinus listed for North America north of Mexico, collectively found across most of the continent. Approximately 190 species are known worldwide, on all continents but Antarctica. The specimens I was watching measured an estimated 8-10 millimeters in size, but some species are larger and others smaller.

I may have to go back and see if I can find more of these interesting sand wasps. I hear they are even active on extremely hot days, and we have had a lot of those this year in Colorado Springs.

Sources: Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge, Massachusetts: Harvard University Press. 526 pp.
O’Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca: Comstock Publishing Associates (Cornell University Press). 406 pp.

Wasp Wednesday: Hoplisoides nebulosus

I continue to be pleasantly surprised by the diversity of wasps here on the Front Range in Colorado Springs. The multitude of plant communities, and ecosystems that change with even a moderate rise in elevation, mean there is an abundance of niches for various members of the Hymenoptera. Last Tuesday, July 10, while prowling a vacant lot in my neighborhood, I discovered yet another genus in the family Crabronidae: Hoplisoides.

The female wasp, about 8-10 mm in length, was scratching the sandy soil at my feet when I spotted her. Initially, I thought she was a mason wasp, owing to their behavior of scraping dry soil for use in their mud nests, and the splayed wings that are characteristic of eumenids. Closer inspection of my first image revealed her to be a crabronid wasp in the genus Hoplisoides, with trademark spotted wings.

The wasp took off but flew just above the ground and eventually landed again at a spot of disturbed sand where she had apparently started digging earlier. She resumed excavating that spot and I spent at least half an hour shooting images each time she emerged from the burrow to deposit her diggings and groom the entrance to disguise the location of her nest. The behavior of digging in several spots before selecting one site to finish is apparently not unusual (Evans, 1966)

There are about eighteen species of Hoplisoides in North America north of Mexico, collectively distributed over the entire continent, including Alaska. The bulk of the species are western. Globally, the genus is found everywhere except Australia.

Most North American species hunt adult and immature treehoppers in the family Membracidae (example below) as food for their larval offspring. Females dig relatively short burrows in sand, the tunnels terminating in one or several underground cells.

“My” wasp was preparing just such a nest, and after completing it filled in the entrance, effectively obliterating all evidence of her work. She made a low “orientation flight” before taking off to hunt prey. I only hope that she did not use me as a landmark. I could hear her “voice” later: “Dang. I seem to remember some big hulking object right here….”

She entered and exited her burrow head first, in contrast to most burrowing wasps that back out of the nest during its construction. The typical burrow descends at an angle of 45-70° for roughly ten centimeters and a depth of about six centimeters. The terminal cell or cells are about 9-11 millimeters long, and 7-9 mm in diameter. An average of 10-15 paralyzed treehoppers go into each cell, but that can vary dramatically depending on the size of each prey item. The larger the prey species the fewer are needed. A single egg is laid on the last victim to go into the cell. Most female wasps make at least a handful of individual nests in their lifetime. It should be noted that the above description pertains to Hoplisoides nebulosus, found mostly in the eastern U.S., and the species depicted here.

Hoplisoides do not spend much time on the final closure of their burrows, so are often victimized by parasites. The cuckoo wasp Elampus viridicyaneus is one such enemy. So are crabronid wasps in the genus Nysson. The velvet ant Dasymutilla vesta may be another parasite; and the “satellite flies” of the family Sarcophagidae (Senotainia trilineata being one) are an ever-present threat lurking in the vicinity of nests.

You will rarely see Hoplisoides on flowers, but you might find them around aphid colonies. They are fond of “honeydew,” the sugary liquid waste product secreted by aphids. Catalpa trees and oak trees are often good places to look for aphid colonies. The constant rain of honeydew will ake the leaves appear glossy or sweaty. Otherwise, encounters with these treehopper hunters are pretty much serendipitous.

Note: The wasp specimen imaged here has since been identified as Hoplisoides nebulosus spilopterus by Matthias Buck at the Royal Alberta Museum in Edmonton. Thank you, Dr. Buck!

Sources: Evans, Howard E. 1966. The Comparative Ethology and Evolution of the Sand Wasps. Cambridge: Harvard University Press. 526 pp.
O’Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, New York: Cornell University Press. 406 pp.