Ed Yong recently reposted his fantastic 2008 post on assassin bug camouflage to keep us entertained while he’s away. I covered the same paper on an old incarnation of my blog, and can’t resist joining in on the reposting fun. Kevin Zelnio of Deep Sea News also has a post about it.
Remember that scene in Silence of the Lambs where Hannibal Lecter kills one of his guards, cuts the poor bastard’s face off and then wears it as a mask so he can escape in an ambulance? This great (if only for the appearance of Chris Isaak as a SWAT team captain) movie moment, it turns out, is something of a case of art imitating life.
While disguise and camouflage have a long history in the animal world (stick bugs, chameleons, decorator crabs, etc.), the assassin bug Acanthaspis petax, takes things to a Lecter-esque extreme.
The order of insects called Hemiptera is comprised of some 80,000 species, collectively known as true bugs. The order’s defining characteristic the arrangement of the bugs’ mouthparts: the mandibles and maxillae have evolved into a sheathed proboscis capable of piercing tissue and sucking out liquids. Most hemipterans use their proboscises to suck sap from plants, but the assassin bug prefers to stab them into other insects (usually ants) and inject their prey with paralysis-inducing saliva and digestive enzymes in order to break down and suck up bodily fluids.
A few other types of insect do the same thing. So what? Well, Acanthaspis petax one ups its brethren and sticks the corpse of its meal to its back, which secretes fine, sticky threads. There the corpse sits with others like it, forming a coat of bodies that earlier research suggested might protect the bug from predators.
Robert Jackson and Simon Pollard from the University of Canterbury tested this theory by matching the assassin bugs against jumping spiders in a no-holds-barred insect cage match. Three species of jumping spider which – all stalking, vision-guided predators that wouldn’t be able to detect the assassin bug by smell - were placed in glass cages with either with naked, unmasked, assassin bugs or bugs bug wearing the bodies of its last few meals.
All three species of spider went after the uncovered bugs about ten times more than the covered ones (even if the bugs were actually dead and preserved decoys the authors used to control variables associated with using live bugs, like motion, behavior, size etc.).
Jackson and Pollard suggest that the cloak of corpses (or skin coat, if you will) successfully deters predators because the bodies break up the assassin bug’s form into something the spiders don’t recognize. They see a mound distinct from the background, but they dont recognize it as prey.
The remaining question is: why ants? Assassin bugs feed on a variety of other insects they encounter, but their camouflage is consistently composed mostly of ant corpses. Jackson and Pollard suggest the possibility that the spiders avoided the cloaked bugs because ants are formidable prey, using chemical defenses and having a nasty tendency to swarm. The assassin bugs, then, might be using ants in particular as disguises because of their tough guy reputation.
Reference: Jackson, R., & Pollard, S. (2007). Bugs with backpacks deter vision-guided predation by jumping spiders Journal of Zoology, 273 (4), 358-363 DOI: 10.1111/j.1469-7998.2007.00335.x