"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

November 19, 2020

Microgaster godzilla

While there is an oft-mentioned quote by evolutionary biologist JBS Haldane that God has an "Inordinate Fondness For Beetles", it is becoming apparent that a different group of insects may be more deserving of being considered as the chosen ones. A recent study estimated that there are actually 2.5 to 3.2 times as many hymenopterans (the insect order that contains ants, bees and wasps) as there are beetles. Furthermore, much of the diversity within the hymenopterans are parasitic wasps, making those parasitoids the most species-rich group of animal on this planet. 

So rather than beetles, the animal group which the hypothetical Creator is most fond of appears to actually be body-snatching parasitic wasps - a sentiment that I can wholeheartedly endorse. And it is one of those wonderful insects which is being featured in today's post. 

Top: Female adult Microgaster godzilla from Figure 1 of the paper
Bottom: Frames showing the parasitisation process, from the supplementary videos of the paper

This post is about a recently described species of parasitic wasp - Microgaster godzilla - which has been named after that famous King of Monsters, Godzilla. While its species name may have attracted much of the attention - not surprisingly, given it has been named after one of the most famous movie monsters in the world - to me, that is the least interesting thing about this insect. Because unlike those many thousands of parasitic wasps out there, M. godzilla has evolved to use an aquatic insect as its host - a very rare feat among these parasitoids. 

Microgaster godzilla belongs to a subfamily of wasp called Microgastrinae, a diverse group composed of 2000 described species. But Microgasterinae itself belongs to a much larger family of parasitic wasps called the Braconidae which contains 17000 known species, with an estimated 42000 species in total. All braconid wasps have larval stages that develop attached to or inside the body of another insect, and when they are ready to mature into full-fledged adults, the endoparasitoid types come bursting out of the body of their hosts like a xenomorph chest-burster.

But for all their diversity and success in using the bodies of other insects as living incubators for their babies, most parasitic wasps are limited to parasitising terrestrial insects, with only 150 species (0.13% of all known hymenopterans) having been recorded to parasitise aquatic insects. Microgaster godzilla belongs to this very special and exclusive club, going where few other wasps are able to venture. 

The target which M. godzilla is after are the aquatic larvae of the moth Elophila turbata. These water-borne caterpillars feed on floating aquatic plants such as duckweeds. They do so usually by burrowing into the plants' leaves, and the older caterpillars, which have grown too large to burrow into the tiny leaves of those aquatic plants, actually weave a casing around itself from bits of vegetation. So at every stage of the caterpillar's development, not only is it submerged, it is also enclosed in a casing of plant material, one way or the other. 

Microgaster godzilla searches for its target by carefully walking on the leaves of duckweed and other floating vegetation on the water surface. But sometimes, it will take the plunge and dive briefly underwater in its hunt. Once it spots the caterpillar's characteristic case, instead of just forcing its way through with brute force, it annoys the caterpillar leaving its protective shelter. Microgaster godzilla starts tapping incessantly on the caterpillar's case with its antennae, accompanied by some prodding with its stinger-like ovipositor. 

Eventually, all this ruckus coaxes the caterpillar into popping out of its cosy plant bag. As soon as that happens, M. godzilla will pounce on the caterpillars and stab it with its ovipositor, injecting eggs in the process (you can view videos of this via the supplementary material which the paper's authors have provided here and here). 

The extraordinary sets of behaviour adaptations displayed by this tiny wasp, which allows it to do something that few other parasitoid wasps are capable of, is just as fascinating as the power of any movie monsters.


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