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The Fly That Banks On Arachnophobia

The views expressed are those of the author and are not necessarily those of Scientific American.

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Imagine that you are a tasty, tasty fruit fly, full of luscious lipids and useful proteins. Just the sort of meal over which any self-respecting fly predator should salivate.

Now imagine that the predatory spiders incessantly stalking you are, like most spiders, solitary creatures. Spiders, you see, are usually happy to avoid their own kind. They find each other to be rather good eating, after all, so the hermit life tends to be the long life.

What to do?

Well, you can always use an arachnid’s rather ironic arachnophobia against itself. That is precisely the defensive strategy of some Rhagoletis fruit flies1. Have a look:

Rhagoletis walnut fly

Having trouble seeing the spider? Try the same photograph in black & white:

Now compare with an actual jumping spider:

A jumping spider.

The visual acuity of spiders is such that their prey can use an optical illusion against them.

That’s pretty cool.

1- further reading:
Eisner, T. (1985). A Fly That Mimics Jumping Spiders. Psyche 92: 103-104.
Mather MH, Roitberg DB (1987) A sheep in wolf’s clothing: tephritid flies mimic spider predators. Science 236: 308–310.

Alex Wild About the Author: Alex Wild is Curator of Entomology at the University of Texas at Austin, where he studies the evolutionary history of ants. In 2003 he founded a photography business as an aesthetic complement to his scientific work, and his natural history photographs appear in numerous museums, books and media outlets. Follow on Twitter @myrmecos.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. WarrenL 7:59 pm 02/23/2012

    Great post!
    You might find the spider easier to see at

    Link to this
  2. 2. Alex Wild 8:02 pm 02/23/2012

    Ha! That’s awesome, Warren. The mimicry is obvious in rear view.

    Link to this
  3. 3. WarrenL 8:11 pm 02/23/2012

    Sorry – changed it to this link:

    Link to this
  4. 4. MorganJackson 8:42 pm 02/23/2012

    Was just about to bring up WarrenL’s point; many fruit flies both in the genus Rhagoletis and other genera have similarly banded wings (see my recent review of northeastern fruit flies to see similar wing patterns in other genera – and often strut around open leaves with them held down and at an angle away from the bodies, waving back and forth. Viewed from the front (or the back obviously), their wing patterns look very similar to the stance of a jumping spider (more so than that of the dorsal view even). The classic theory was that this behaviour was a mating display, and it wasn’t until the mid 1980′s that they were observed evading a spider predator! In fact, the very next paper in the issue after the Mather & Roitberg paper you referenced has a picture of a related species, Zonosemata vittigera, staring down a jumping spider ( and living to tell the tale.

    Amazing flies with incredible morphological & behavioural adaptations to survive!

    Link to this
  5. 5. BDNf.cyno 9:45 pm 02/23/2012

    Interesting! And the rear view is indeed great to really “get” it.

    Link to this

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