Toxic, Hairy Caterpillars Descend on London, Prompting Health Warning

If you see one, inch away.

In an extremely true story that would be a worthy inclusion in the Sharknado universe, a swarm of poisonous caterpillars has descended upon London. The epidemic of oak processionary moth (OPMs) larvae is an annual occurrence, resulting in a rash of warnings from the U.K. Forestry Commission and a rash on those unfortunate enough to cross paths with the toxic critter.

The OPM is an invasive species in the United Kingdom — it appears that even nationalist Brexit fervor wasn’t enough to keep it away. The insects are native to Southern Europe, where predation and environmental conditions keep the population in check. In Britain’s largest metropolis, however, the moths flourish even with significant human intervention.

In their larval state — when they are caterpillars — OPMs are covered by thousands of minuscule hairs that contain an irritating protein called thametopoein. Physically contacting or inhaling these hairs routinely causes skin rashes and can induce sore throats, difficulty breathing, and eye problems in people who have severe allergic reactions. The caterpillars shed these hairs naturally but also cast them off as a defense mechanism — presumably to ward off creatures like parasitic wasps, who implant their eggs inside of caterpillars through a sting. Throughout these natural processes, unfortunately, humans are often collateral damage.

OPM larvae are covered by thousands of toxic hairs.


“My first symptom was a rash on my tummy. I was unaware of what is was and thought at first it was a heat rash,” a gardener who inadvertently came into contact with the larvae told the BBC last week. “During this time I had spells of feeling violently sick. I thought I might have shingles.”

Because of these unfortunate effects, the U.K. Forestry Commission issued a warning to steer clear of the bugs and their nests. They even have a reporting system called “Tree Alert” for citizen entomologists to report any OPM sightings.

While OPMs are particularly active in early to mid-May, they will have settled into nests for the pupation process by July. After a few months of feeding on oak leaves and constructing silken dens, the caterpillars retreat to their abodes for a few weeks before emerging as full-fledged moths. For three glorious days, the OPMs lay eggs on oak trees before promptly dying. The eggs start to hatch the following spring, and the cycle begins anew.

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