Insects Never Fail to Amaze

Recently I saw my first ever specimen of Archaeognatha. I was going to write on that, so I picked up the lab's faithful copy of The Insects of Australia (CSIRO, 1991) to look up information. Before I found the Archaeognatha chapter, however, I came across something else that just blew me away so much that I had to share it with you all. Meet the freaky little marine midge Pontomyia (the only image I could find online was a rather blurry one here. Sorry).

There are very few marine insects, and only a single genus, the waterstrider Halobates, has species that are actually found on the open ocean (van der Hage, 1996). Other marine insects are restricted to inshore habitats. Pontomyia appears to be an inhabitant of tide pools and lagoons in the West Pacific. It belongs to the large family Chironomidae, mosquito-like (but non-parasitic) midges with aquatic larvae

Individuals of Pontomyia spend most of their lives as benthic larvae. After they emerge as non-feeding adults, they only live for a couple of hours (Soong et al., 1999). In this brief time, they must find a mate and produce eggs.

Pontomyia adults emerge at dusk or after sunset. At least one species, Pontomyia oceana, only emerges around the new and full moons (in combination with the specific emergence time, this probably ensures that the females end up laying eggs at low tide). Pupae swim to the surface and emerge as adults. The females are vermiform and structurally degenerate, with seemingly little activity as far as I can tell.

The males are the freaky ones. They skim the water surface film on the tips of the stout second and stilt-like, trailing third pairs of legs. The first pair of legs is immensely long and curve out on either side of the body as a pair of 'outriggers', barely skimming the surface and maintaining the animal's balance. The paddle-like wings propel the midge by flicking the air just above the water surface (Norris, 1991).

Females do not complete emergence from the pupa unless males are nearby (Soong et al., 1999). Males generally emerge up to an hour before females, and have been observed stripping the pupal skin from females to help them emerge. Once a male has found a female, he picks her up with the second legs and the base of the third legs and carries her while mating. Males are apparently quick movers, and I was especially taken by this sentence in Soong et al. (1999): 'They did not appear to slow down after catching females, sometimes climbing the vertical substrate up to 15 cm above the water level while dragging a female along'. One can't help wondering what Germaine Greer would make of the verbs in there.

After mating, the male drops the female. She lays her eggs on bits of dead coral or the like sticking up about the water surface in long interconnected strings. And that, as they say, is that.

REFERENCES

Norris, K. R. 1991. General biology. In The Insects of Australia (CSIRO, eds.), 2n ed., vol. I pp. 68-108. Melbourne University Press.

Soong, K., G.-F. Chen & J.-R. Cao. 1999. Life history studies of the flightless marine midges Pontomyia spp. (Diptera: Chironomidae). Zoological Studies 38 (4): 466-473. (Pdf here)

van der Hage, J. C. H. 1996. Why are there no insects and so few higher plants, in the sea? New thoughts on an old problem. Functional Ecology 10: 546-547.