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With rain beating down upon the snow, I’m hiding indoors today. This seemed like a good afternoon to spend some time sorting insect photos from 2005. With many thousands of photos stockpiled in two drives, sorting photos sometimes makes me feel a bit like Hercules trying to clean out the Augean stables. I suppose the worst of it is that the 2006 insect season isn’t too far off, so this year’s photos will soon be piling up atop of last year’s. Yikes! However, it’s not an unpleasant way to soak up some hours. Opening up each batch of files is almost like uncorking a bottle of summer air and sunlight.

Today, I spent a few minutes working on the ID for a clearwing moth that I photographed last August (see above). I’m quite sure that it must be a Raspberry Crown Borer moth (Pennisetia marginata). Apparently, some people refer to them as “hornet moths” for rather obvious reasons. It belongs to that group of insects referred to as “mimics” — the many species of insect impostors that mimic the appearance and behaviour of other insects, or even of spiders. As I like to work very closely to the insects that I photograph, with my hands often just an inch or two away, it pays to know who’s who.

A good wasp mimic can be quite convincing even at very close range. Take the fly in the above photo. At first glance, it looks uncomfortably like a wasp or hornet — perhaps a Bald-faced Hornet (Dolichovespula maculata) such as the one to the left (click to see larger photo). However, it’s actually a Spilomyia sp (I believe S. sayi), a large fly that mimics both the appearance and behaviour of a hornet. It is often found feeding atop flowers in the company of hornets and bees. If it feels threatened, perhaps by a photographer sticking a macro lens in its personal space, it will turn to face the intruder while holding its smoky, hornet-like wings angled out into an aggressive “attack position” while causing them to gyrate in a somewhat alarming fashion. Even though I have photographed these flies on several occasions, at a subconscious level, I often find it difficult to convince myself that I’m in no danger of being stung. From a defensive point of view, this fly has got its “scary act” down to a science.

Some insect impostors use their mimicry for perncious purposes. For example, with their thin-waisted bodies, colored bands, and angled wings, flies belonging to the family Conopidae (example to the left – click for larger view), masquerade as wasps while feeding on the nectar of flowers among the bees which they ultimately hope to lay their eggs upon. In this case, looks can and do kill, as the larvae of these flies parasitize and kill the host bees.

Among the many mimics I’ve photographed, this small fly (see below), was most surprising. It’s a Rhagoletis sp.(I believe a R. striatella), which is considered a fruit pest. I found it while trying to photograph a mason bee on a nearby leaf. I just caught a glimpse of this fly out of the corner of my eye and instinctively pulled my hand away, thinking that it was actually a Zebra Jumping Spider (Salticus scenicus), which have somewhat pugnacious tendencies. After giving it a closer look, I realized that the spider was actually a fly — one that hopped about, waving and curling its boldly marked wings in such a way that they seemed to resemble the raised front pairs of legs of a jumping spider. The combination of its markings, its wing movements, and its feisty behaviour was most convincing. Again, it was one of those cases where the eye and the mind had a difficult time coming to a consensus on the identity of the impostor.

All said, the insect impostors are an interesting lot. While shape and markings can be quite convincing on their own, it’s the behavioral mimicry that probably fascinates me the most. The bold performances of some of these insects can be truly remarkable.

Tags: Raspberry Crown Borer moth, Pennisetia marginata, Bald-faced Hornet, Dolichovespula maculata, Spilomyia sayi, Conopidae, Rhagoletis striatelle, Salticus scenicus, mimic, insect impostor