Eight Illinois Wasp and Bee Mimics in Twenty Minutes

One of the few entomologically-rewarding stops on our recent road trip was at the National Trail Rest Area on Interstate 70 near Altamont, Illinois, on May 16. A brief bit of sunshine warmed the woodland edges enough to bring out a wealth of fly diversity, many of which were mimics of various wasps and bees. There were even a few real wasps.

Somula decora syrphid fly

Large patches of touch-me-nots (aka "jewelweed") carpeted the edges of the lawn where it gave way to forest, and the leaves of this plant offered places to bask for many insects. The first fly I spotted was one of my favorites in the family Syrphidae (flower flies). Somula decora is roughly the size of a honey bee, black in color but heavily marked with golden yellow. I suspected that this species is a mimic of scoliid wasps, but at this time of year a more likely candidate for a model would be a queen yellowjacket.

Helophilus sp. syrphid fly

Helophilus spp. are also probably yellowjacket mimics. The vertical yellow stripes on the thorax help to identify them fairly easily. Apparently the larvae develop in decaying plant matter that is submerged in water, as do other Syrphidae species like the "rat-tailed maggots." The adults certainly are sun-loving as their genus name suggests.

Temnostoma sp. syrphid fly

Syrphid flies in the genus Temnostoma are likely mimics of the solitary mason wasps that are in the same family as the social yellowjackets. They carry their mimicry to astonishing extremes. Note that the leading edge of their wings is darkened, mimicking the longitudinal folds of a vespid wasp's wings at rest. Wasps have long, reasonably thick antennae, which Temnostoma flies don't have. No worries, the fly compensates by waving its front pair of legs in front of its face, just like wasp antennae. Wh-a-a-a-a-t?! I know! Next time I'll take video.

Male Ancistrocerus sp. mason wasp

Well, lookie lookie, here comes an honest-to-goodness, certifiable mason wasp. This is a male, as the tip of each antenna is hooked, a distinguishing characteristic for many male eumenine wasps. I am a little hard-pressed for a genus, but I suspect it might be Ancistrocerus. Female mason wasps usually nest in pre-existing cavities like old beetle borings in logs, hollow twigs, etc.

Chalcosyrphus piger syrphid fly

Yet another kind of syrphid fly we saw was this Chalcosyrphus species. They are typically assumed to be mimics of solitary wasps in the families Pompilidae, Crabronidae, or Sphecidae. Indeed, some species even flick their wings like wasps while they run around on foliage or the surface of logs. Their larvae live in decaying wood, but at least a few may feed on fermenting sap. This species has a red abdomen, but others are wholly black or otherwise colored differently. There are 22 species in North America, so identification is difficult without putting a specimen under a microscope.

Xylota sp. syrphid fly

Closely allied to Chalcosyrphus is the genus Xylota. Oddly, this specimen reminded me most of a sawfly or an ichneumon wasp, neither of which is usually capable of stinging in self-defense. The adult flies rarely visit flowers, instead feeding on pollen grains from the surface of leaves. The larvae develop in rotting wood.

Mallota posticata syrphid fly

Many syrphid flies use leaves as a platform on which to groom, which explains the yoga-like moves of this specimen of Mallota posticata, a bumble bee mimic. I swear, grooming flies must be the envy of contortionists. As larvae, these flies grow up in rotting holes in trees.

Eastern Yellowjacket queen, a real wasp!

My, my, here we have another actual wasp, a queen of the Eastern Yellowjacket, Vespula maculifrons, pausing from her search for an underground nesting site. She is likewise grooming. This particular species is very likely the "model" for most of the "mimic" flies we were seeing....and arguably the best mimic was yet to come.

Sphecomyia vittata syrphid fly

The syrphid fly Sphecomyia vittata is simply stunning. It is about the same size as a queen yellowjacket, and even has longer, thicker antennae than almost any other fly, the better to resemble its sting-equipped model. This insect even flies like a queen yellowjacket, in the lazy, zig-zag manner of a queen looking for a nesting site. I recall capturing one of these in Cincinnati and being convinced it was a wasp right up until I had it in the jar. I was jaw-droppingly impressed.

Ichneumon wasp

Ah, here is an ichneumon wasp that looks suspiciously like that Xylota flower fly we saw a few minutes ago. At least some members of the subfamily Ichneumoninae can sting, so maybe looking like one is a better strategy than first imagined.

Laphria sp. robber fly

Somewhere along the line my wife spotted this fly, which I never saw. It is obviously a bumble bee mimic, but it is not a syrphid. It is a robber fly in the family Asilidae, genus Laphria. Looking like a bumble bee works to its advantage in two ways: its potential predators assume it stings. Meanwhile the fly's potential prey assume it is a bee seeking flower nectar. Interestingly, Laphria seem to be particularly fond of small, flying beetles, which they spot from their perches, apprehend in mid-air, and return to a leaf or log to feed upon.

Common Gartersnake, Thamnophis sirtalis

What a rewarding rest stop. Oh, and there was this bonus Common Gartersnake, Thamnophis sirtalis, also soaking up some rays. It never moved an inch as we worked around it to take insect images. Thanks to the maintenance crews at this rest stop for recognizing the importance of leaving natural elements intact around the area, including dead wood for insects to feed on, and birds to nest in. May other states follow your example.

Source: Marshall, Stephen A. 2006. Insects: Their Natural History and Diversity. Richmond Hill, Ontario: Firefly Books, Ltd.732 pp.

The "News Bee"

It is Fly Day Friday, and I have been neglecting the Diptera for far too long. Last week, my wife Heidi and I were in Ohio where we saw many striking members of this order. Friday, August 23, we hiked the trail to Buzzardroost Rock, a preserve maintained by The Nature Conservancy in Adams County (south central Ohio). Near the top of the ridge we heard a loud buzzing and saw a large insect hovering in the sun near a large log. Periodically it would perch on a leaf or the ground and it was then apparent what it was: a flower fly in the family Syrphidae. This particular species was the spectacular Milesia virginiensis.

At 18-28.5 millimeters in body length, and brightly colored in yellow, brown, and black, this fly could easily be mistaken for a European Hornet or queen yellowjacket. The ominous droning buzz it makes only heightens the visual mimicry. Some speculate that this species mimics the Southern Yellowjacket, Vespula squamosa. Indeed, Southern Yellowjackets were also active in the area, but the workers are substantially smaller than this fly. It is too early for the yellowjacket queens to be appearing, but they make for a better “model” in both size and color pattern.

Milesia virginiensis figures in American folklore and superstition. It is still known in many hamlets as the “News Bee,” for it will sometimes hover in front of a person, as if it were “giving them the news.” It is also considered to be good luck if one of these flies alights on your finger. I was surprised that this particular individual allowed me a very close approach, so maybe it is not out of the realm of possibility than one of these insects could perch on a patient person.

Perhaps the idea of these flies broadcasting the local gossip stems from confusion with real bees. Another old wives’ tale suggests that a bee buzzing in one’s ear means that important news will arrive shortly.

Larvae of the News Bee apparently feed in the wet, rotting heartwood of stumps and logs, which might explain why this adult fly showed so much interest in the log. Males might recognize a log as a potential resource for females to lay eggs in, and guard a territory around it.

This species is found throughout most of eastern North America, from Kansas to Minnesota and Ontario, south to Texas and Florida. Nowhere does it seem to be abundant, however. Look for the adults from late May to November in southerly latitudes, and mid-summer to early fall elsewhere. Two other species in the genus, M. bella and M. sctutellata range in the southwest U.S. and southeastern U.S. (southeast Oklahoma to North Carolina), respectively.

Milesia virginiensis is also known as the Yellowjacket Hover Fly and the Virginia Flower Fly. While there are records of them visiting Queen Anne’s Lace, Rattlesnake Master, and other wildflowers, I personally have not seen them nectaring. Almost invariably, I find them hovering in sunny spots in the understory of hardwood forests.

Sources: Coin, Patrick, et al. 2012. “Species Milesia virginiensis - Yellowjacket Hover Fly,” Bugguide.net
Skevington, Jeff H. 2012. “Field Guide to the Syrphidae of Northeastern North America,” Canadian National Collection of Insects, Arachnids, and Nematodes.

Wasp Wednesday: Not Wasp III

When it comes to mimicry of wasps, the flower flies of the family Syrphidae are perhaps unequaled. They are convincing enough that I myself remain prone to being fooled by some of these imposters. Among the best of the best are members of the genus Spilomyia, which not only look like yellowjackets, but even sound like them.

A recent trip to Colorado Springs, Colorado revealed just how easy it is to pull the wool over my eyes. At the Cheyenne Mountain Zoo I had been seeing both Aerial Yellowjackets (Dolichovespula arenaria) and Western Yellowjackets (Vespula pensylvanica) licking aphid honeydew off of leaves on a young aspen tree. One of the “yellowjackets” didn’t look quite right, though, and a closer inspection revealed it to be a fly.

One way I am able to tell flower flies from yellowjackets is by the antennae. Yellowjackets have long, thick antennae, whereas most of the flies have very short antennae with a hair-like appendage called an arista on the very tip. Some flower flies, including those in the genus Spilomyia compensate for this difference by waving their front legs in front of their faces to simulate the longer, thicker antennae of the wasps.

Fine. I can always tell the difference by the eyes. Flies have very large eyes that meet at (males) or near (females) the top of their heads. This should be easy. Ok, wait a minute, exactly where do this fly’s eyes end and the rest of its face begin? Swell. The ornate black and yellow markings on the fly’s eyes now make sense: they break up the outline of the eyes, making them appear smaller than they actually are.

Alright, I don’t give up that easily. Flies have only one pair of wings, while wasps have two. Ha! I got you now. Also, the wings of yellowjackets are folded longitudinally when the wasp is at rest, so the wings appear thinner and darker….Uh oh. This fly actually has the front half of each wing darkened to mimic that fold. Unreal.

The flies are also the same size as yellowjackets, varying from 12-17 millimeters in body length. But, as if visual appearance and behavior are not enough to convince a would-be predator not to mess with the fly, this mimic even sounds like a wasp. The frequency of its wingbeats in flight is nearly identical to that of its yellowjacket model. One has to wonder if any predator or parasite can see (and hear) through this charade.

Flower flies are more than just a pretty face, though. The adults visit flowers, and they can be at least adequate pollinators as a result of this behavior. The larval stages of Spilomyia apparently dwell inside water-filled tree holes, feeding on decaying organic matter. So, they are valuable recyclers and decomposers, too.

The next time you think you see a yellowjacket in your yard or garden, do a double-take; maybe a triple-take. You might just be seeing a fly in disguise. Spilomyia is a very widespread genus with about 13 species in North America, so chances are good that they are in your neighborhood.