Insects Are Cool, Too

One of our esteemed Entomology lecturers has for the past few weeks been preaching doom and gloom about the immediate future of ENTO304 participants’ insect collecting prospects. ‘Hope you've done all your collecting: it’s getting too cold for insects!’ he warns us. ‘The weather’s turning!’ And it’s true. If there’s one thing that’s good about winter, it’s the diminishing of pesky houseflies in our flat. It came as some surprise, then, when I discovered a whole book dedicated to the Entomology of Antarctica. When I think of life in Antarctica, I think penguins, and that’s pretty much as far as I get. But what if I were to tell you that the biggest terrestrial animal in Antarctica is actually an insect? What if I were to add that there are more insect species in Antarctica than any other Antarctic animal?

How can this be? What does Antarctica have to offer insects apart from ice? Not much, it turns out, but enough…

I use ‘insect’ in the loosest term: from sea-level to 2000 metres above, Antarctica is home to over 50 species of arthropod. They can be divided into two categories based on the type of habitat they exploit: half are the the-answer-is-right-under-your-nose parasitic kind, and half are the how-on-earth-do-they-do-it free-living kind.

Antarctica: more than just penguins

The parasitic arthropods, which include lice, ticks, a single species of flea and parasitic mites, are probably the easiest to understand. Sucking lice live on the seals of Antarctica, and ticks, biting lice and parasitic mites live on Antarctica’s birds. Even when diving, warm-blooded animals are able to provide these invertebrates with a much warmer habitat than could otherwise be found, and a considerably greater stability of microclimate which means such arthropods need little in the way of their own homeostatic mechanisms. Parasitism is also the obvious choice in a depauperate environment in terms of a ready and guaranteed food supply. Desiccation, the main adversary of the free-living insects, is significantly less of a problem for creatures small enough to live under the protective, waterproof layers of feathers or fur. Colony behaviour of the majority of Antarctic birds and seals facilitates the dispersal of these invertebrates.

Not all of Antarctica is covered in ice, and not all of it is covered in ice all year round. Antarctica’s free-living arthropods - midges, springtails and non-parasitic mites – can be found in habitats involving such diverse geomorphology as snow-melt streams, old lava flows, freshwater or brackish ponds, scree-slopes, moraine deposits, soil and exposed stone. Because all Antarctica’s large vertebrate fauna are marine rather than terrestrial, these arthropods are Antarctica’s only terrestrial animals. 

Antarctica: more than just penguins with lice

Compared to the parasites, the free-living arthropods are much more subject to the forbidding environment that we normally associate with Antarctica: extreme cold and extreme dryness. Temperature, as with all insects, determines activity levels of these arthropods and thus habitats that receive the most sun in summer, such as northward facing slopes, are more frequently inhabited. Though generally preferring of the dark, the warmed rocks provide a microclimate that allows the arthropods to move. Ultimately, however, arthropod distribution is restricted by moisture. 

Antarctic mites

The free-living arthropods live in close proximity to plants, which in Antarctica means mosses, lichens and algae; though fungi, liverworts and grasses may be found in more northern areas. These primary producers provide the invertebrates with food and moisture. Combined, this is the simple entirety of Antarctica’s terrestrial ecosystem. Springtails, the least desiccation-tolerant, are usually found amongst moss roots, while mites, the hardiest, inhabit a wider variety of rocky areas which can be comparatively drier - porous rock cavities and the underside of shales near temporary melt-water rivulets are common habitats.

Two Belgica antarctica

You can’t get very far into Antarctic entomology without coming across Belgica antarctica: Antarctica’s largest (roughly 0.5 cm long) endemic terrestrial species and the flightless version of only two true Antarctic insects, the midge. This species breeds in brackish waters and lives near pools and streams associated with mosses. Recent studies on B. antarctica have found that, due to their high desiccation tolerance, the midge larvae are able to utilise a vapour gradient in the presence of ice that reduces the melting point of their body fluids so they don’t freeze over winter. All the free-living arthropods are dormant through the winter in whatever developmental stage they have reached. Few populations of any of these arthropods show great annual stability, changing seasonally according to local migrations in response to moisture gradients. Suitable areas of habitation are also those that are sheltered from Antarctica’s strong winds, which can increase the rate of desiccation and lower temperatures; though it may be a dispersal mechanism for springtails which have been collected from the air with nets.

Perhaps it is ironic or perhaps it is poetic that the largest land mass in the southern hemisphere should have the smallest terrestrial ecosystem consisting of some of the smallest macroscopic life, or perhaps it is just amazing that such animals can be found here at all. Regardless of your take, the fact remains: Antarctica is more than just penguins. 

Antarctic springtails amongst moss

Thanks to Insect Habitats in Antarctica by J. L. Gressitt and R. E. Leech for opening my eyes.