By Duncan Geere, Wired UK

A species of assassin bug has been found which creeps onto spiders' webs and pretends to be prey, then devours the spider when it comes to investigate.

The creature, known to entomologists as Stenolemus bituberus, is the subject of a paper just published in Proceedings of the Royal Society B by Annie Wignall from Macquarie University in Sydney, Australia. Wignall describes the exact process of "aggressive mimicry" by which the assassin bug stalks its target.

Most predators conceal themselves in order to capture prey, but the assassin bug takes the opposite approach – overtly advertising its presence in a way that entices its dinner to investigate. Web-building spiders use vibrations in their web to detect when it's caught something, so they can go over, bind it in more web, and eat it.

The assassin bug slowly approaches the spider on its web, using its forelegs to pluck the silk threads in a manner that simulates the vibrations of a fly struggling after being caught. Wignall studied the behavior of the bugs, and found that the response of the spider to the predator was the same as its response to when a vinegar fly or aphid was caught in the web.

Once the spider is close enough, the assassin bug lashes out, and eats the poor unsuspecting arachnid. Most of the time, anyway – Wignall also observed a few occasions of spiders counter-attacking the bugs and killing and eating them instead.

Wignall points out that the assassin bug doesn't identically replicate the vibrations caused by prey – there are several higher-amplitude vibrations that prey generate which aren't simulated by the bug. But the spider doesn't seem to be able to generally differentiate between the two.

The work could have implications for the physics of how vibrations propagate through three-dimensional webs.

Images: 1) Flickr/jeffsmallwood. 2) An* assassin bug. Flickr/dhobern*

Source: Wired.co.uk

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