Dehydrated, frozen, ocean bound, irradiated: The insects which go to extremes
By: Gary Hartley
Tags: Nature, Insects, Ecology, Climate, Extreme

The red flat bark beetle: made for extreme cold, but doesn’t compare with others below. Photo: Judy Gallagher

Insects tend to scutter perilously on the dividing line between life and death. Moderate behaviours in moderate environments are far from standard — but there are some species that push things further than most to eke out a living.

Enter the extreme survivalists: the bugs which make Bear Grylls’s efforts appear pretty tame.

The driest fly

The excellently-named midge Polypedilum vanderplanki, known as the ‘sleeping Chironomid’, seems like a good place to start. This super fly’s larvae live in temporary pools and can survive their habitats drying out completely. Given this extremophile species lives in semi-arid parts of West Africa with a prolonged dry season, this is an excellent quality to possess.

The trick is to slip into a state of near complete desiccation, or anhydrobiosis. We’re talking down to 3% water content, with the body shrinkage that goes with it. That noted, P. vanderplanki, at around 7mm, is the largest animal that is known to be able to enter this state.

When undergoing its transformation to as close to a husk as a living insect can get, bodily water is replaced with sugars, protectant proteins and anti-oxidants. This change in bodily substance prevents cellular damage and, ultimately, death.

Super dry stays alive. Image: Cornette and Kikawada, 2011

Hardcore, across the board

Unbelievably, the ability to live in a waterless pool in blazing sun is not the limit of P. vanderplanki’s wild tolerances. Survive high doses of radiation? Exposure to a vacuum? Submersion in liquid helium? Tick, tick and tick. Researchers reckon that this package of extreme traits is genetically linked — as in, the cellular changes that occur during anhydrobiosis also serve as a useful barrier against almost any extreme nature can throw at it.

There’s something about midges of the Chironomidae family that draws them to extremes. Paraborniella tonnoiri larvae can survive heat shock and desiccation, while Polypedilum cf. tamanigrum works its way through heat shock and acid conditions. It’s hard not to react with some sadness at the idea of an adult of any of these extremophiles, having completed their arduous juvenile life cycle and emerged as an adult, falling victim to a fly swatter.

A brief mention to the broader assemblage of insect species living in arid conditions. There are many adaptations made for life under the blazing sun, from the physiology of Namib desert beetles designed for water collection, as mentioned in a previous post, to the Sahara desert ant with its long legs ensuring minimal contact with hot sand to avoid heat exposure, while scavenging for the corpses of those invertebrates that weren’t so well adapted.

Seaborne survivors

The true bugs of the genus Halobates may not strictly be considered extremophiles, but given that only five species of insects, all from this group, choose to make a living on the open sea, they are well worthy of inclusion. Let’s call them extremophile-adjacent.

Whereas as a number of insects live on shorelines, the sea itself is an altogether more unforgiving habitat, with fresh water and shelter from climatic conditions at a premium and prey scattered unpredictably. The quest for life as an insect should, in theory, be pushed to its limits — but Halobates spp. find it to their taste.

A fine picture of a sea skater

The bodily form and style of movement of Halobates spp. will be familiar to anyone who’s gone near a pond, lake or stream in the warmer months. They are known as sea skaters, cousins of the less adventurous but no less skittish pond skaters.

Halobates species live in the Pacific, and survive by feeding on other creatures inhabiting the surface of the ocean, while dodging those that want to eat them. They lay their eggs on pretty much anything floating — which has led them to an interaction with that most notorious of human pollution: microplastics.

Research has shown that as microplastic concentrations have increased, so has egg-laying by Halobates sericeus. This doesn’t necessarily lead to bigger populations of this sea skater, due to knock-on effects in this strange ecosystem, such as the tiny crab Planes minutus feeding on the abundant eggs. For those mining the planet’s more sparse ecological niches, even the dregs of the Anthropocene can prove something of a life support.

Overwintering beetle is supercool

Hacking the cold is a speciality of Cucujus clavipes puniceus, an Alaskan bark beetle. Its larvae can survive drops to -100 °C, though even in Alaska they are likely to face at least slightly less severe cold as they strive to complete their life cycle under the bark of fallen trees. Small mercies and all that.

Like P. vanderplanki, it adapts to extremity by losing body water, and in its case, increasing concentrations of antifreeze proteins and glycerol. High levels of dehydration are linked with ‘deep supercooling’ abilities — the only thing that will ensure survival way down the double digits below freezing.

C. clavipes puniceus cannot be considered king of the cold, however.

Antarctica’s sole insect faces ultimate test

Judging by the number of species that live there, Antarctica has to go down as the ultimate speciality insect habitat. The continent has just the one insect: Belgica antarctica, the Antarctic midge. It’s pretty much the ‘poster insect’ of the extremophiles, and another member of the Chironomidae. Seriously, what is it with this family?

This midge in particularly is wingless (I mean, there aren’t too many flight windows available faced with highly regular blizzard conditions) and at under a centimetre, is the largest exclusively land-dwelling animal native to the continent. These are arguably not its most notable qualities, however. That might be reserved for the fact that it survives being frozen for three quarters of the year.

Why would you do this to yourself, B. antarctica? Source: Phys.org

One part of B. antarctica’s response to extreme cold stress is the accumulation of a potent antifreeze mix which includes glucose, erythritol and trehalose. They also give a hefty dose of antifreeze to their eggs, when infrequent egg-laying opportunities arise.

This change in bodily chemical composition is coupled with desiccation, which while not quite as impressive as P. vanderplanki, can involve the loss of up to 70% of its water content. These adaptations are crucial in preventing ice forming within the body to fatal effect. If the cold wasn’t enough to contend with, it can also stoically hold its own against other stressors such as UV radiation exposure and oxygen deprivation.

As with pretty much everything in entomology, the exceptional traits of B. antarctica can be explained by its genetics — and in particular, it’s notably tiny genome, the smallest of any insect to date. It’s fair to say that this a genome that focuses on the essentials needed for the environment it’s in, with lots of genes linked to development, metabolism and response to outside stimuli.

The mighty cold midge makes the most of a cellular phenomenon known as autophagy (literally: ‘self-eating’), which sounds bad, but in this case is about cell survival in cases where they might otherwise die. It has been suggested that the stress of dehydration causes a process of accelerated ageing, but autophagy steps in to provide something of a ‘cell recycling’ process.

For the record, when B. antarctica larvae are not frozen, they are generalist feeders on dead plant matter, microorganisms and fungi. Admittedly, their life history outside of the big freeze almost seems a bit of side note.

The hard life of a worker bee or ant in a temperate climate is certainly put into perspective next to these hardcore animals. It’s tempting to ask ‘why bother?’, but our human concepts of logic are of no concern to the insects. If an ecological niche is available with few rivals, or even none at all, there tends to be a bug there. For them, a life of seemingly horrific duress is better than none at all.