Wasp Wednesday: Podoschistus

I was wrong. I have to admit that a lot in my entomological world. I think I know what something is and I am incorrect. When I came across this sleek female ichneumon wasp I assumed it was probably a species of Rhyssa given the size, shape, and behavior (climbing around on the trunk of a tree). Turns out it is actually a specimen of Podoschistus vittifrons.

I always have other people to thank for helping me see the error of my ways, and this time the credit goes to Bob Carlson, a world-class authority on ichneumonids of North America. My image is not the greatest, but still he was able to discern the identity of the wasp.

Ok, so there is only one North American representative in the genus Podoschistus, but….The classification of ichneumons has changed numerous times, and no doubt will continue to be modified in the future. This particular wasp was formerly placed in the genera Xorides and Neoxorides. It is a member of the small subfamily Poemeniinae, and is known to be ectoparasitic on the larvae of wood-boring beetles.

Apparently, P. vittifrons is not commonly encountered in the forest habitats it frequents. This specimen was imaged near the foot of Mount Sugarloaf in South Deerfield, Massachusetts. There are remnant woodlands there, but the majority of the surrounding landscape is farmland and more-or-less suburban housing. Recorded hosts for its larvae are the grubs of Dicerca divaricata (family Buprestidae) and Graphisurus fasciatus (family Cerambycidae). Left alone to mature into an adult beetle, G. fasciatus looks like this:

The female wasp somehow “divines” the presence of a beetle grub boring in the bole, then inserts her long, needle-like ovipositor through the wood to reach the grub and lay an egg upon it. The wasp larva that hatches then slowly consumes the beetle grub.

Those who are interested in a more detailed diagnosis of the Poemeniinae will find this web page exceedingly detailed and useful. Illustrated keys to subfamilies of world Ichneumonidae can be found in Hymenoptera of the World: An identification guide to families edited by Henri Goulet and John T. Hauber (Agriculture Canada, 1993).

Ichneumons in general provide enough diversity in appearance and habits to last one a lifetime of study should he or she be so inclined. There is certainly much more to learn about them, their geographic distribution, and their hosts.

Spring (Butterfly) Beauties

Spring has definitely “sprung” here at the Tucson Botanical Gardens. Many flowers are in bloom, and native butterflies are taking full advantage of the bounty of nectar. We are now up to forty (yes, 40) confirmed butterfly species seen on the grounds. Recent observations have yielded some surprises, including one supposedly rare species of skipper.

The “usual suspects” are here: Pipevine Swallowtail, Giant Swallowtail, Checkered White, Southern Dogface, Sleepy Orange, Dainty Sulphur, Gray Hairstreak (image above), Marine
Blue, Reakirt’s Blue, Fatal Metalmark, Gulf Fritillary, Texan Crescent, American Snout, and Painted Lady. What is new, then? Plenty.

One of the more startling species I spotted a couple weeks ago was a Desert Orangetip, Anthocharis cethura. Just as I focused my camera on it, away it flew. That figures. I haven’t seen one since, either.

Another mild surprise was a Mourning Cloak, Nymphalis antiopa (image below). This large, black butterfly with a creamy border is more typical of riparian areas since it feeds on willow in the caterpillar stage. This male specimen was frequenting the bird garden. He perched where he had a good vantage point and darted out after any intruder, especially other butterflies like Pipevine Swallowtails. After a brief chase he returned to the same area he started from. He even alighted on a visitor’s ballcap while I was watching.

The real shockers have come from the skippers in the family Hesperiidae. Sure, the Fiery Skipper, Orange Skipperling, Common Checkered-Skipper, and Eufala Skipper are common enough, but I’ve seen other species that I would not expect here. The first of these was a Sleepy Duskywing, Erynnis brizo, seen on March 4 (image below). This species feeds on oak as a caterpillar, so it really belongs a couple of thousand feet higher in elevation. There it was, though, on a Dalea blossom in the butterfly garden.

The Funereal Duskywing, Erynnis funeralis, is a much more likely species here at the Gardens. I finally spotted one on March 19, but failed to get a picture. This fast-flying skipper is fairly large. Mostly black, it has a blazing white border along the edge of its hind wing which makes it easily identifiable.

Another surprise was an Arizona Powdered-Skipper, Systasea zampa (image above), sitting on a brick in the barrio garden late in the afternoon of March 6. I initially figured it for a Fatal Metalmark, to which it bears superficial resemblance.

The Golden-headed Scallopwing, Staphylus ceos, also resembles a metalmark at first glance.

The most amazing of all the spring skippers was a Violet-clouded Skipper, Lerodea arabus. It is relatively non-descript (see image below), save for a distinct dark brown patch on the underside of its hind wing. Certainly no violet to be seen! You would think that this would be among the more abundant of butterfly species given that the caterpillar feeds on Bermuda grass, barnyard grass, and other weedy plants. Instead, most reference books list it as “rare.”

Last but not least, I added a species by proxy. One of the visitors to the Butterfly Magic greenhouse, Carolyn Vieira, mentioned to me that she also takes pictures of butterflies on the TBG grounds. I told her I had yet to see a Great Purple Hairstreak, Atlides halesus, and as luck would have it she had a picture she took a couple years ago or so. I still expect to see this spectacular butterfly here myself, but it is nice to have an existing record.

The diversity of wildlife to be found at the Tucson Botanical Gardens continues to astound me. Just in cursory observation I’m closing in on 200 species of animals, from arthropods to apes (we Homo sapiens). The wide variety of plants, and the constant watering no doubt provides a literal oasis for all.

Wasp Wednesday: Tachysphex

People ask me how I became interested in insects in general and wasps in particular. If I answer honestly to the second part of the question, I must admit I probably pursued wasps because no one could call me a sissy for catching something that can fight back. Indeed, I’ve been stung a few times, but not nearly as many as you might imagine. Most wasps are solitary, and females simply don’t have large numbers of helpless eggs, larvae, and pupae to defend. Such is the case with wasps in the genus Tachysphex, family Crabronidae.

These are diminutive insects, averaging only 6-10 millimeters in length. They sure do pack a lot of energy into that tiny body, though. Watch one and try not to get dizzy. They are so high-strung that you’d swear they drink the wasp equivalent of double-shot espresso. Their quickness is essential to their success at catching prey, fending off parasites, and evading predators.

I was lucky enough to find the specimen above in a state of near torpor, one morning at Wild Outdoor World Arizona. This is basically the only time I’ve seen one sit still. Females are usually going to town digging a burrow or seeking prey. The most accurate records of prey indicate that Tachysphex uses mostly grasshoppers (Acrididae) as hosts, but katydids (Tettigoniidae), crickets (Gryllidae), cockroaches (Blattodea), and mantids (Mantodea) are provisioned by some species. Immature (nymph) stages of those insects are stung into paralysis by the female wasp. She flips the helpless victim onto its back, grabs one of its antennae in her jaws, and cradles it with at least one pair of legs. She will fly her prize back to the nest or haul her heavier cargo overland.

The wasp excavates a shallow burrow in sand or soil before going hunting. The female shown in the remaining images here was being thwarted by the asphalt of the road shoulder she was on. Once she got through the thin layer of fine gravel and other debris, there was that damn pavement….every time!

An underground tunnel dug in a suitable substrate usually includes multiple cells where the prey are stored. One to eight or more victims are placed in each cell depending on their size, a single egg laid on the underside of the thorax of the last one into the tomb.

Among the enemies of Tachysphex are those pesky satellite flies (Sarcophagidae: Miltogramminae), bee flies (Bombyliidae), velvet ants (Mutillidae), and cuckoo wasps (Chrysididae, including Hedychridium). All are parasitic on the larval Tachysphex and/or consume the insect prey provided by the female wasp for her offspring to eat.

Watch for these tiny little busy-bodies, but don’t expect to find them easily. I have rarely seen them visiting flowers. Mostly, you catch a glimpse of them darting around on the ground, among weedy vegetation in open habitats. There are roughly 43 species in North America, collectively ranging across the entire continent (into the Northwest Territories in at least one case, the Yukon in another). No doubt more species await formal description, or even discovery.

Butterfly Love

Spring is in the air here in Tucson, Arizona, and apparently the thoughts of butterflies are turning to love. I wrote the following for the Valentine’s Day issue of the volunteer newsletter at the Tucson Botanical Gardens, but cruising the grounds this past week I saw plenty of native butterflies in “action,” so to speak, like this pair of Giant Swallowtails outside our administration building.

Visitors to Butterfly Magic will never fail to notice when two butterflies are conjoined, and will ask you what is going on with that. Well, ok, so the butterflies themselves are not shy when it comes to courtship and sex. They have a limited amount of time to find acceptable mates and produce the next generation.

Among the more dazzling behaviors butterflies engage in is courtship. There are great differences in courtship behavior from family to family, and even species to species, but you can easily recognize certain postures and flight styles as romance-intended. Females may advertise their availability by perching with wings open and abdomen slightly raised. She may also “call” males by releasing a special chemical called a pheromone. Males detect the wind-wafted scent with their antennae and then quickly recognize her visually. Male giant silkmoths like the African Moon Moth and the Forbes Moth can home in on a female from up to a mile away (maybe even longer) by following her pheromone trail.

Male butterflies of many species have pheromones, too, designed to communicate individual fitness to a potential mate. Once he locates a female the male must convince her he is a worthy investment. He may do this by following her in flight until she lands, then hovering over her and showering her with his own “cologne” emitted from special scent patches on his wings, or from “hair pencils,” glands that he extrudes from the rear of his abdomen. Males of some Heliconiinae (longwings) go a step further and sprinkle an anti-aphrodisiac once mating has occurred. This discourages other males from usurping his genetic investment in that particular female’s offspring.

Should the female be disinterested in a suitor, she changes her posture, pointing her abdomen nearly straight up and essentially “mooning” the male.

The pursuit and hovering displays are characteristic of the male Priamus Birdwings and the Heliconius longwings. Morphos are less elegant. Males will land next to perched females and aggressively “nudge” them into compliance. Watch as a male bends his abdomen forward in an attempt to copulate.

Compatible males and females may eventually couple, tail-to-tail, facing in opposite directions. Males might even hang limply from the female as she remains perched. Occasionally the pair will even take flight, one of them carrying the other. Butterflies can remain coupled for as little as a few minutes to several hours. We had one pair of Priamus Birdwings (shown above) engaged for so long that the male actually perished while still connected to the female. While lengthy mating leaves both butterflies vulnerable to predation, it also prevents other males from mating with a given female, increasing the odds that the male will see some of his genes represented in the next generation produced by that female. Nature is full of such trade-offs.

Butterflies have the same sex organs as other animals, but they go by different names. The male penis is called an aedeagus (ee-dee-AY-gus). The shape and configuration of the aedeagus varies from species to species, largely preventing hybridization between different species. He also has claspers, the external genitalia that hold the couple together during sex. The female has a vagina (the “bursa copulatrix”), but also has a “receptaculum seminis” or “spermatheca,” a sac that stores sperm. Her eggs will not be fertilized until she lays them.

Whew! I managed to get through all that without even talking about contraception and the Butterfly Vatican.

A pair of Texan Crescents is shown above.

Wasp Wednesday: Agathidinae

”Why the long face?” is a question that could be asked of some members of the subfamily Agathidinae in the family Braconidae. The narrow, extended face is characteristic of the genera Agathis, Bassus, and Cremnops, helping to make them recognizable in the field (though they can still be confused with other kinds of Ichneumonoidea).

These are also often colorful wasps, clad in red and black, with black or smoky wings. At 6-10 mm, they are small in size, but larger than many other kinds of braconid wasps. They are also frequent visitors to flowers, which sets them apart from most others in the family Braconidae. They make use of those elongated mouthparts to probe for nectar.

The female wasps also hunt caterpillars to lay their eggs in. Typically, one wasp larva develops as an internal parasite of a host caterpillar, though some species are gregarious, several larvae sharing the same caterpillar host. A select few species are occasionally employed as biological control agents. There are 99 species in the subfamily in North America, according to this recent synoptic review of the Agathidinae.

Lots of confusion remains concerning the classification. M. J. Sharkey recently resurrected the genus Lytopylus, splitting it from Bassus, for example. The generic identity of the specimen imaged here, just a few days ago, remains a mystery since I did not collect the specimen, and do not have access to an electron microscope, about the only tool able to render enough detail to facilitate identification at the genus level.

Still, it can be satisfying being able to recognize these insects as braconids in the first place. Most braconids are easily confused with ichneumon wasps of similar size and appearance.

Sources: Marsh, Paul M., Scott R. Shaw, and Robert A. Wharton. 1987. “An Identification Manual for the North American Genera of the Family Braconidae.” Memoirs of the Entomological Society of Washington. Number 13: 98 pp.
Sharkey, M. J. 2004. “Synopsis of the Agathidinae of America North of Mexico,” Proceedings of the Russian Entomological Society. St. Petersburg. Vol. 75(1): 134-152.

Wasp Wednesday: Wasp/Not Wasp

Previously on “Wasp Wednesday” we featured keyhole wasps of the genus Trypoxylon. Like most stinging insects, these wasps are models for other harmless insects that escape predators by pretending to be something more dangerous than they are: a sheep in wolf’s clothing if you will. Meet Pseudodoros clavatus, a near perfect imposter of a keyhole wasp.

A biologist friend once cautioned me on jumping to conclusions about which insects serve as models for various mimics, but just look at this fly. The elongated abdomen even has pale markings to make it appear narrower than it actually is. At 7-12 millimeters long, it is also similar in size to many Trypoxylon wasps. Besides looking like the wasp, the fly even behaves like it. Male keyhole wasps often hover in front of vertical objects, and the fly hovers just as well, if not better than, the wasp.

Ok, so how do you tell them apart, anyway? Above is the wasp. Note that it has two pairs of wings (though connected to each other they are usually still discernible as separate). The antennae of the wasp are thick and relatively long. They eyes are large, but do not take up the entire head or face of the wasp. Now look at the fly below. It has only one pair of wings. The antennae are so short they are scarcely visible. The eyes cover most of the head of the fly, and are not notched on the inner margin like those of the wasp.

Pseudodoros clavatus is a member of the family Syrphidae, collectively known as “flower flies” (“hover flies” in Europe). They are frequent, abundant visitors to flowers of all kinds. While they may be insignificant pollinators, they play their part in perpetuating wildflowers. Their good deeds extend to the larval stage as well. The maggots of Pseudodoros are voracious predators of aphids.

Seeing one of these slug-like larvae on your rose bush might lead you to think that it is also eating the plant, but watch one closely and you will see it methodically slaying aphids, seizing the tiny sap-suckers and hoisting them off the stem. The fly larva then sucks the hapless pest dry and discards the empty husk of its exoskeleton.

Look for this species from coast to coast in the United States and southern Canada. It may be confused with the similar genera Baccha and Ocyptamus in some parts of its range, but Ocyptamus species have at least faint dark markings on the wings (if only a bold leading edge to the wing). Baccha is more difficult to distinguish, but at least one species has a distinctly banded abdomen. The image below is still a Pseudodoros.

Wasp Wednesday: Trypoxylon

Last week I reported on the “Keyhole Wasp,” Pachodynerus nasidens, but mentioned that there are other kinds of wasps that also go by that common name. Meet the members of the genus Trypoxylon in the family Crabronidae. Most species of these spider-hunting wasps nest in pre-existing cavities, such as old nail holes. They are common, but usually go unnoticed by the casual naturalist.

Trypoxylon wasps can be separated from other wasps by a couple of distinctive characters. The abdomen is long, slender, and clavate (club-shaped, the tip of the abdomen being decidedly blunt). There is only one submarginal cell in the forewing. Lastly, the compound eyes are emarginate, meaning they are obviously “notched” in the middle, on the inner margin.

The genus is divided into two subgenera, the small species in the subgenus Trypoxylon, while medium-sized and large species are in the subgenus Trypargilum. Both groups are collectively distributed over most of the North American continent. The only ones I have managed to image in the wild so far are species of Trypargilum. Despite their larger size, they defy identification to species without collection of actual specimens. However, their shared life cycles are similar enough to generalize.

Adult females are solitary, and seek natural cavities in which to nest. This typically means hollow twigs, old beetle borings in dead, standing trees, vacated insect galls, and abandoned nests of mud dauber wasps. Those natural tunnels are progressively partitioned into individual cells along their length as the wasp first provisions the deepest one, then moves forward toward the entrance.

Interestingly, the males often participate in nest maintenance, at the least by actively guarding the nest entrance while the female is away hunting prey or harvesting mud for one of the partitions. This is extremely valuable because the nest is besieged by parasitic insects that would find easy pickings were it not for the male wasp’s devotion to duty. Males do not sting, but they physically block entry of parasites and behave aggressively toward those enemies. Observers have also noted that in some species of Trypoxylon the males may take prey brought in by the female and place it in the cell while she resumes hunting. Males can also assist in cleaning out the cavity before nesting begins, and aiding in the building of partitions and the mud plug closing the finished nest. Naturalist Phil Rau called those species demonstrating couples teamwork “Patriarchate wasps.”

The two species found commonly here in Tucson, T. californicum and T. clavatum clavatum, average from 1-5 cells per nest. Spiders are the prey of these wasps, and mostly immature spiders at that. Some species hunt mostly web-building spiders, while other species seek free-ranging spiders, but there always seems to be at least a slight degree of overlap in prey selection. Jumping spiders, crab spiders, running spiders, lynx spiders, and sac spiders are recorded prey for T. californicum. The same general prey base applies to T. c. clavatum, but also add small wolf spiders and a good selection of orb weavers. Anywhere from 5-20 spiders are stocked in each cell, sometimes more, occasionally less (3 is the recorded minimum, 36 the maximum).

One egg is laid in each cell, and the larva that hatches consumes the cache of paralyzed arachnids. When mature, the larvae spins a cocoon. Apparently, the composition and architecture of the cocoon is species-specific, with varying amounts of silk, saliva, and soil going into the matrix. Inside the cocoon the larva pupates, and an adult wasp eventually emerges.

I would be remiss if I failed to mention that there is one species in North America that breaks all the rules. That would be the “Pipe Organ Mud Dauber,” Trypoxylon politum. This is a very large wasp for the genus, glossy black with white “ankles” on the hind legs, and it constructs large, linear mud nests that resemble the pipes on an old-fashioned organ. This wasp ranges over most of the U.S. east of the Great Plains. You can learn more about it in this excellent archived entry from ”This Week at Hilton Pond” and at Bugguide.net.

You can create habitat for the cavity-nesters by simply drilling holes in a block of wood and hanging it up under an eave on your home, shed, or barn. One pair of researchers here in Tucson used a ¼ inch bit drilled to a depth of 77 millimeters, and a 3/16th inch bit drilled to 124 millimeters, with good success. A good primer on how to build such “trap nests” can be found here. Give it a try!

Sources: Matthews, R.W. and J.R. 1968. “A note on Trypargilum arizonense in trap nests from Arizona, with a review of prey preferences and cocoon structure in the genus.” Psyche 75: 285-293 (available online as a PDF. T. arizonense is an outdated name for T. californicum).
Bohart, R.M. and A.S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.