Caterpillars may seem like harmless creatures, but some of them are anything but. Certain subspecies can be highly toxic in a byproduct of evolution that has equipped these largely powerless larvae with a self-defense mechanism. Londeners are learning this to their own cost.
Parts of England’s capital are being invaded by oak processionary caterpillars (Thaumetopoea processionea), which are the larvae of moths that live on oak trees. The long white hairs of the caterpillars contain toxins that can cause allergic reactions in humans, including skin and eye irritation, difficulty of breathing and even anaphylactic shock.
People who come into contact with the hairs break out in painful rashes on large parts of their body. If they’re lucky, that is. “At best, you can get contact dermatitis. At worst, you can die,” an expert in insects explains. “You can go into anaphylactic shock and have your airways close up. The airborne hairs set up a whole different ballgame.”
To make matters worse, each caterpillar boasts more than 62,000 fine hairs that can easily get airborne and can stay toxic for up to five years. With the arrival of spring the larvae hatch from their eggs and begin swarming around oak trees, which they may end up decimating by devouring their leaves in large quantities.
But here’s the kicker: the moths, and their caterpillars, aren’t native to the British isles. They are an invasive species that first arrived 13 years ago.
They’re part of an invasion of southern European species making their way ever further up north. Aiding them in this has been climate change, which is causing temperatures to warm on the northern half of the continent.
Make no mistake: even otherwise harmless-seeming invasive species can wreak havoc with local ecosystems. Take Eastern grey squirrels. They’re cute-looking creatures that were introduced from the US into Britain a century or so ago.
The small rodents are now hardy perennials in many a park around the UK, but they are not as innocuous as they may seem. They can damage trees by stripping them bare of their bark, thereby exposing their timber to harm from fungi and insects. They can also spread disease to other animals and to humans.
Invasive non-native species like toxic caterpillars and grey squirrels also cost countries financially. According to government estimates, in the UK alone they cost taxpayers £2 billion (€2.26 billion) each year.