While many male songbirds in beautiful, bright breeding plumage can easily catch our eye this time of year, invertebrates emerging after winter are easier to overlook but can be just as wonderful. I noticed the sartorial splendor of one insect, the golden-backed snipe fly (Chrysopilus thoracious) the last week in May. After two days of rain, the sun came out and so did this fly, which began a brief but frenzied orgy of mating in the forest edge bordering my yard.
This fly, about a half-inch long, is among one of the many insect species that have evolved to mimic hymenoptera (bees and wasps) in coloration. Flies, especially hoverflies, are particularly known for mimicry, but even some moths and beetles also have this adaptation. Some, such as hoverflies and the snowberry clearwing moth (Hemaris diffinis, also called bumblebee moth), go as far as mimicking the hovering flight pattern of hymenoptera as well.
The reason for the deception is to evade predators, which tend to avoid bees and wasps because many species of the latter can deliver a painful, even lethal, sting. It takes a bit of effort to sort out the hymenoptera from their mimics, but I found a reference sheet on the University of Illinois’s BeeSpotter website that helps, complete with detailed drawings.
Golden-backed snipe flies have transparent wings with clearly delineated black veins (a trait typical of snipe flies) forming lovely patterns that remind me of the art nouveau period at the turn of the 20th century, which was influenced by design motifs found among animals and plants.
Golden-backs also sport white rings around their black, tapered abdomens. Although the rings don’t quite meet in the middle of the fly’s back, they help in simulating many species in the hymenoptera family. The visual accent that gives this fly its name is the lovely golden, furry patch on its back. Lying just behind its head, this is patch is especially reminiscent of bumblebees.
Although the coloration of golden-backed snipe flies is similar to that of some bees, there are two easy ways to tell any fly from a bee, according to the BeeSpotter site: Bees have four wings, while flies have two; and bees have elbowed antennae (bent at a joint in the middle), while flies tend to have short, stubby or hair-thin antennae that are straight. As the site puts it, “if you can’t see the antennae, you’re probably looking at a fly.”
Like hoverflies, snipe flies are among the 120,000 or so members, worldwide, of the order Diptera, or true flies, according to the Mountain Lake Biological Center of the University of Virginia, which has good information on the golden-backed. Most sources acknowledge not much is known about this species, although more is known about snipe flies in general than other fly species, according to the site.
One thing sources agree on is that, like other snipe flies, the golden-backs are associated with damp forest or thick vegetation. Their larvae, according to the Audubon Society’s “Field Guide to North American Insects & Spiders,” develop in rotting wood or moist soil, where they prey on small insects.
While some snipe flies are fierce biters, the golden-backed is not among them. The Audubon guide says the adults prey on aphids and other small insects. However, other sources say that, while the adults are thought to prey on insects, they have not been observed doing so and suggest that the adults may not eat at all. Such disinterest in eating is common in many insects whose brief adult lives are focused on procreating. Adult golden-backs only appear at the end of May through early June to breed. Their job done, they die, leaving another generation to emerge as larvae later in the summer.
The two genders of golden-backed snipe flies are dimorphic (differ in form): The females are larger — or “more robust,” as the Mountain Lake site puts it — and the male’s eyes, which are larger than the female’s, are also holoptic (meeting at the top of the head), unlike the female’s.
This fly’s mating process is similar to that of many flying insects: The male backs up to the female and extends his penis to deliver sperm into her reproductive parts, which in most flying insects include a chamber or storage sac for sperm. With the golden-backs, as with many animal species, the transaction can last a while. While I neither observed nor found more information on courtship, most species, even such simple ones such as these flies, have courtship rituals that involve more than a “quickie” and can be quite elaborate.
When landing on vertical surfaces, such as tree trunks, snipe flies face downward, so are referred to as “downward-lookers” by entomologists. The Audubon guide adds that the golden-backed, when approached, “runs or sidles rather than flies.” I personally haven’t seen the sidling behavior, but most of the golden-backs I’ve observed have been at rest or mating. While photographing mating pairs, I found that a couple, likely feeling threatened by my presence, flew rather than sidled off, still joined together. When I went out a couple of days later to see if I could observe the sidling behavior in individual flies, I couldn’t find any. Maybe next spring.
© 2014 Pam Owen