"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

February 24, 2015

Gelis agilis

It's a bug-eat-bug world out there and the same applies to parasitic wasps - even parasites can themselves become parasitised - which is why some parasitoids recruit their dying host as defence. The parasitoids that go after other parasitoids are call "hyperparasitoids" and the species we are featuring today is Gelis agilis, a tiny wingless wasp that lays its eggs in the cocoons of parasitic wasps such as Cotesia glomerata.
Photo of Gelis agilis by Christophe Quintin

This hyperparasitoid wasp has more to contend with than just overcoming their host's reluctant bodyguard. It is after all a small insect which equates to a handy mouthful for many potential predators. The adult G. agilis is a tiny (3-5 mm) and seemingly defenceless - it doesn't even have wings to fly away from any danger. But G. agilis makes up for that with a clever masquerade

If there is a group of tiny insect which are generally regarded as pretty unpalatable, it is ants (except for animals that specialise on eating ants), so many other creatures have evolved to mimic them in one way or the other. When it comes to playing the part of an ant, G. agilis is a method actor - not only does it look and act like an ant, it even smells the part. When agitated, it emits a volatile chemical call sulcatone, which is the same chemical used by ants as alarm pheromone to rally colony members to their defence.

This "full spectrum mimicry" pays off. Spiders that normally pounce straight onto similarly-sized insects such as fruit flies or parasitic wasps like C. glomerata would hesitate or back right off when confronted with Gelis. A species related to G. agilis - G. aerator - looks and acts like an ant but lacks the distinctive "antsy" smell. When G. aerator was put through experimental trials up against hungry wolf spiders, most spiders back off due to its ant-like appearance. But the lack of matching ant BO was enough for a few more daring (or desperate) spiders to get the jump on G. aerator.

By playing the part to its fullest capacity - behaviour, appearance, and scent - G. agilis is better able to evade its predators to survive another day, and go on to make life a living hell for other body-snatchers

Malcicka, M., Bezemer, T. M., Visser, B., Bloemberg, M., Snart, C. J., Hardy, I. C., & Harvey, J. A. (2015). Multi-trait mimicry of ants by a parasitoid wasp. Scientific Reports 5: 8043

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