Do people know there are aquatic wasps? Because there are aquatic wasps. At least 150 species of them.
The degree to which they live their life in water varies, but almost all of them parasitise aquatic insect larvae – with the exception of the spider wasp Anoplius depressipes, which parasitises fishing spiders instead – and their offspring have to swim back out once they emerge as adults. A lot of them have longer claws than other wasps to help with gripping vegetation underwater and hairs that can trap air and make them somewhat hydrophobic. And they're all largely unrelated, they're thought to have evolved being aquatic at least 50 times separately!
Anoplius depressipes
One neat one I want to point out is Caraphractus cinctus. It's a fairyfly (Mymaridae), and if you've heard of them, you've probably heard they're small enough that they essentially swim through the air with their feather-like wings. C. cinctus takes that a little further by. Well. Swimming. They emerge as adults from the parasitised eggs of diving beetles (Dytiscidae) and the females immediately begin searching for new eggs, moving through the water using their wings and taking in oxygen from the water. They are seemingly able to survive for up to 15 days below the surface, and if beetle eggs are available then most females never do leave the water. Mating usually occurs underwater, although not within the beetle eggs as the Bennett paper says. I find it really cool that they can break through the surface tension by diving in head first, although they tend to just use vegetation to help them down.
From Jackson (1958)
Another really cool one is Hydrophylita emporos, which sometimes locates its host's eggs by catching a ride on the adult female damselfly's (Psolodesmus mandarinus mandarinus) abdomen and running down to lay their own once she starts ovipositing. Some, like C. cinctus, stay below the water their whole lives.
Hydrophylita emporos on the back of Psolodesmus mandarinus mandarinus, CC BY 2.5
Also, one of them is named after Godzilla (Microgaster godzilla). I think that's very important
Bennett, A.M.R. (2008) 'Global diversity of hymenopterans (Hymenoptera; Insecta) in freshwater', Hydrobiologia, 595, pp. 529–534
Jackson, D.J. (1958) 'Observations on the biology of Caraphractus cinctus Walker (Hymenoptera: Mymaridae), a parasitoid of the eggs of Dytiscidae (Coleoptera) – I. Methods of rearing and numbers bred on different host eggs', Transactions of the Royal Entomological Society of London, 110(17), pp. 533–554
Jackson, D.J. (1961) 'Observations on the biology of Caraphractus cinctus Walker (Hymenoptera: Mymaridae), a parasitoid of the eggs of Dytiscidae (Coleoptera) – II. Immature stages and seasonal history with a review of Mymarid larvae', Parasitology, 51(3–4), pp. 269–294 (not really referenced here but this isn't an essay it doesn't need to be one to one right)
Jackson, D.J. (1966) 'Observations on the biology of Caraphractus cinctus Walker (Hymenoptera: Mymaridae), a parasitoid of the eggs of Dytiscidae (Coleoptera) – III. The adult life and sex ratio', Transactions of the Royal Entomological Society of London, 118(2), pp. 23–49 (these three are unfortunately not open access but if you can use sci-hub then 👀)
Shih Y.T. et al. (2013) 'Hydrophylita (Lutzimicron) emporos Shih & Polaszek (Hymenoptera: Trichogrammatidae) from Taiwan, parasitising eggs, and phoretic on adults, of the damselfly Psolodesmus mandarinus mandarinus (Zygoptera: Calopterygidae)', PLoS One, 8(7), e69331
Fernandez-Triana, J. et al. (2020) 'Microgaster godzilla (Hymenoptera, Braconidae, Microgastrinae), an unusual new species from Japan which dives underwater to parasitize its caterpillar host (Lepidoptera, Crambidae, Acentropinae)', Journal of Hymenoptera Research, 79, pp. 15–26
