Peter Convey

Nematodes might be stretching things a bit for an insect week! But they are an important part of the Antarctic fauna, along with other microscopic soil animals such as tardigrades and rotifers. The springtails and mites I’ve previously talked about are certainly the most obvious animals you will come across in the areas that most people get the chance to visit the Antarctic continent – near the coast and the neighbouring islands where there is some decent vegetation. When you go inland things rapidly become far more barren to the eye, if still spectacular – the photo here is of an area of the Pensacola Mountains at about 83 degrees south. This is one of a number of places where no insects or other arthropods appear to be capable of existing. But that does not mean there is no life, and a few species of tardigrade and rotifer make up the animal community. Elsewhere, these are joined by nematode worms, and these are some of the simplest animal communities known from anywhere on the planet.

What is so significant about a picture of a hoverfly on a dandelion? After all, there are probably thousands of them doing just that in my garden (aka weed patch) right now, and it’s not even as though it’s a partcularly good picture! But this picture hides a trick question…where was it taken? The answer is the sub-Antarctic island of South Georgia, deep in the South Atlantic Ocean. And there neither dandelions not hoverflies are part of the native flora and fauna. It is a well known truth that, wherever we humans go, we tend to carry other things with us, sometimes deliberately, more often inadvertently. The same is true when we go to the Antarctic but, whereas this process has been happening for many centuries and longer across most of the planet’s continents, our contact with the Antarctic is much more recent, and the intensity of that contact (i.e. numbers of people) much lower. There are still parts of the continent that have seen virtually no human footprints (and I have been privileged to see such places in my work) and, compared to the rest of the world, the actual continent of Antarctica remains largely pristine in the context of alien species. In the Antarctic Treaty system – which effectively is the system used to manage our presence and impacts in Antarctica – we have a clear duty to preserve the Antarctic environment. Which brings me back to the dandelions and the sub-Antarctic islands. These islands are much less extreme than the continent itself, and have typically a couple of hundred years or so of human history, the first three quarters of this being the decades of intense marine exploitation (sealing and whaling) that had such a drastic impact on marine ecosystems. Dandelions arrived on South Georgia at this time, very likely as seeds carried with cargo such as animal fodder. Quite a few other plants arrived at the same time, such that today there are more alien plants on South Georgia than there are native ones (although to be fair most have very limited distributions and haven’t spread far from their introduction site). Of the roughly 200 alien species currently known from the entire Antarctic region, more than 95% are on the sub-Antarctic islands, and half of these are plants and a third insects. Which brings me neatly on to the hoverfly. A peculiarity of sub-Antarctic ecosystems is that they do not include either insect-pollinated flowers, or insects that are pollinators. This is one reason why at least some of the alien plants haven’t spread, as unlike the native species many of them require pollinators. Four years ago, the first hoverfly was seen on South Georgia, and over the last two years it has become clear that this species, which is native to southern South America and the Falkland Islands, is well established in parts of the warmer north-east coast of the island. In terms of how this might impact the local ecosystem, we now have a situation where the ‘brake’ on many alien plants setting fertile seed and spreading rapidly will be taken off, and currently ‘persistent’ species which have little impact may become truly ‘invasive’, possibly leading to major changes in the way the ecosystem functions. Although it seems most likely that the flies would have been carried to South Georgia on a ship, many of which visit each summer, as is often the case noone actually saw the first arrivals, and it is also possible they could simply have been wind-blown from their normal range. However, now they are there, there is no realistic possibility of eradication, hence we simply have to wait and see what the impacts are. And the purpose of highlighting all this? Basically, what has happened so far provides a clear warning of what might happen in future along the Antarctic Peninsula – the ‘next step’ into Antarctica in terms of increasingly severe conditions – especially as this region is one of the three fastest warming parts of the planet at present. The easiest and most practical way of minimising the risks associated with alien species carried by humans is to try and stop them at the point of origin, so they don’t get there in the first place. The reality is that any human activity carries with it a risk of inadvertently carrying a new organism into the Antarctic, but this can be minimised by a whole set of common sense ‘biosecurity’ measures – think about how easy it is to check and clean clothing, boots and rucksacs before you go somewhere new, to pack cargo in clean warehouses and in boxes that do not provide hiding places, to ensure that soil is not carried with fresh foods like potatoes, and so on. If you are ever lucky enough to visit this part of the world, either professionally or as a tourist, keep these simple messages in mind!

True insects are something of an oddity in the Antarctic, at least since taxonomists have taken the springtails (proper name Collembola) and placed them ancestral to rather than within the insects themselves. If we confine ourselves to the Antarctic continent, in fact there are only two of them, although there are a few more on the sub-Antarctic islands (of which more later….). The two properly Antarctic ones are both midges (family Chironomidae). As often happens when you look closely at something small, they turn out to have some particularly interesting characteristics. One species, Parochlus steinenii, is the only flying insect in the Antarctic. It is a South American species which has a toehold – actually a bit more than that since swarms of the adults are visible on the rare calm days – in the South Shetland Islands and on sub-Antarctic South Georgia. The other, Belgica antarctica, has wings that are reduced to tiny stubs (‘brachyptery’), and does its swarming on the ground and moss vegetation when warmed by the sun. The photograph, courtesy of my colleague Rick Lee, shows a mating pair of these ~5mm midges. Belgica is a particularly interesting species, as it is endemic (i.e. only occurs on) the Antarctic Peninsula and South Shetland Islands. This leads to an obvious question of ‘how long have they been there?’ – on the one hand it takes a long time for new species to evolve, but on the other hand, this part of Antarctica is very heavily glaciated – there is very little land and habitat even now – and was more so only ten thousand years ago at the last glacial maximum. Could its habitat, and the fly itself, have survived through the ice ages in Antarctica? Modern molecular biology techniques seem to answer this question with a resounding ‘yes’ – dating the split from Belgica’s nearest known relative (a fly from sub-Antarctic South Georgia, where it is also endemic) at more than 40 million years ago. On the face of it, this is a small and specialised observation…but it has huge implications…if the fly has survived on the Antarctic Peninsula for that length of time, then obviously its habitat must have too, which means we need to revise our thinking about how much more ice there was on Antarctica during ‘ice age’ periods.

Sitting here in an increasingly sunny Cambridge, it is easy to be an entomologist! Our (well, our friends’) bees are up early and foraging, moths are starting to appear in recent numbers in my small moth trap, and those friendly mosquitoes from the nearby fen are obviously hungry… But, when I say I’m an entomologist in Antarctica, the most usual reaction is blank looks! ‘Bugs don’t live in the ice, do they??’ most will say and, strictly, they are right – just like here, the bugs that are around live on the small part of Antarctica that is free of ice and snow, at least in the summer. Even then, most of the larger insects we are familiar with here don’t make it ’south. But, if you look closely, there are plenty to be found – you have to look in the soil and simple vegetation and, if you do, you find a thriving community of springtails, mites, and smaller invertebrates, the largest maybe a millimetre or so in length. So what, I hear you say….well, just like here in the UK, these things are actually the drivers of the soil ecosystem, and are central in reprocessing the dead material that comes into the soil, and releasing their nutrients so they can be used again. Take them away, here or there, and the overall ecosystem will have serious trouble functioning. [/caption]

The picture here (click it to see the full-size version) is of the common Antarctic springtail Cryptopygus antarcticus (they don’t have english names!) – there are several thousand here trapped on a small pool of water on some moss. This tells you they can be very common – I’ve occasionally found densities of more than a million per square metre, more typically tens to hundreds of thousands – that is at least as many as you will find in your garden! There is one other obvious difference though – in our Antarctic habitats we find maybe two species at once, and only twenty or so across the entire continent….in your garden you will probably find several hundred!!