Well, they eat our trees at any rate. These are one of London's less loved immigrants. Unlike the blameless souls to which we referred earlier this week. Processionary caterpillars are what we're talking about, and they are bad bad news: one ends up wondering why they were created in the first place. What have we got against them? Well, they destroy trees for one. They're not too good for humans either. They're toxic little buggers, you see: they scatter powdery stuff which can cause a nasty rash, trigger asthma and even induce anaphlyaxis. And, frankly, they're sinister: the sight of a column of them on the march is strangely stomach churning even for those not usually fazed by creepy crawlies.
They are common in warmer climes: the pine variety has eaten much of Spain and Southern France. But global warming means that they are creeping ever northwards. The Oak Processionary arrived in the UK around three years ago, and settled happily into leafy West London. And this year they are popping up all over the place - Chiswick, Hounslow, Brentford, Isleworth. Good news is that the outbreaks are still fairly minimal, and the forestry commission is on the case. But if you do see any trees thus afflicted (look for nightmarish webby cocoons), tell the nearest ranger/council official pronto.