Mick Hartley

Those aren't other flies sitting on the wings of a bigger fly: those are markings…

[Photo: Peter Roosenschoon]

From last year's paper by Anna Zacharias which first brought this extraordinary mimicry to light, via Andrew Kevkin at the NYT:

[A] closer examination of the transparent wings of Goniurellia tridens reveals a piece of evolutionary art. Each wing carries a precisely detailed image of an ant-like insect, complete with six legs, two antennae, a head, thorax and tapered abdomen.

“The image on the wing is absolutely perfect,” says Dr. Brigitte Howarth, the fly specialist at Zayed University who first discovered G. tridens in the UAE.

It is a member of tephritidae, a family – there are two – of 5,000 species of fruit flies whose colorful markings have earned them the name “peacock flies.”

In the UAE alone, 27 picture wing species are known. Some have wings bearing simple shapes but others, like G. tridens, are far more complex.

Dr Howarth first saw G. tridens on an oleander shrub in northern Oman. “I was looking at the stem of the leaves and I noticed that there were some insects crawling around. When I sort of honed in I started to notice what I thought was a couple of ants moving around.”

At first she suspected an infestation on the fly’s wings. “But it was so symmetrical that I thought, ‘oh this is not possible’. When I got it under the microscope I realized that these were insects painted onto the wings.”

Jerry Coyne tries to make sense of it in evolutionary terms. After assuming at first (along with Kevkin) that these are pictures of ants, he comes round more to the suggestion from a few commenters that they are in fact spiders:

[S]ome tephritids have spider-like markings on them, and that makes more sense.  Apparently the predator is a jumping spider, and when it sneaks up on a fly, it sees the spider markings, mistakes them for another spider of its species, and displays to it. That display gives away the spider’s presence, allowing the fly to get away. 

So yes, it's all a bit speculative. But how astounding that evolution has the power to produce such detailed art.

Of course it shouldn't be such a surprise: evolution has managed eyes (several different ways), peacock's tails, the human brain; so a picture of a spider shouldn't be too much of a challenge. And yet, somehow, it's not quite what you expect….