“Browntail-moth-caterpillar hairs are barbed and hollow. And inside that hollow tube, there’s a reservoir of a toxin,” says Allison Kanoti, the state entomologist for Maine, which is in the middle of a massive browntail-moth outbreak...Portland, Maine’s largest city, has had to temporarily relocate its farmers’ market to avoid the insects’ uncanny habit of dropping down from the trees where they nest. In June, Waterville, a city of 16,000, declared a public emergency because of the caterpillars. And all across the state, shoppers covered in itchy abrasions have stripped drugstore shelves bare of witch hazel and cortisone, key ingredients in a DIY compound designed to soothe the downy beast’s ferocious burn. Brushing up against a browntail-moth caterpillar or otherwise encountering its hairs—on a picnic table, on a dock, on a bit of clothes hung out to dry—can leave a person itching for days as a poison-ivy-like rash creeps across the flesh. And as the caterpillar sheds its hairs, they can go airborne, causing wheezing if they’re inhaled. Both reactions can be so severe it necessitates a trip to the emergency room. Research suggests that getting a hair of a browntail-moth caterpillar in your eye can even cause blindness (though this is exceedingly rare). The hairs can remain toxic for up to three years.“It spread pretty rapidly over 15 years from Massachusetts, to Long Island up into Vermont, New Hampshire, Maine, all the way over to New Brunswick, Nova Scotia, and into Canada,” Angela Mech, an assistant professor of forest entomology at the University of Maine, told me. “It was a huge nuisance.”...The health risk, at least, is seasonal. By late June the caterpillars have entered their cocoons in preparation of becoming moths, and the caterpillars that hatch from eggs in the late summer or early fall aren’t yet poisonous. Their toxins emerge over months as the caterpillars grow in their winter webs, shedding old skin, and revealing a larger new skin underneath, before becoming toxic shortly after they emerge from their webs in April...During the initial outbreak in the 1890s, the browntail-moth caterpillars caused so much havoc that, according to Mech, kids were paid to clip down their tents in winter. In a single year more than 24 million browntail-moth webs were clipped off trees and burned, while federal and local governments introduced dozens of different biocontrol agents, including predator insects from Europe... a fungus known as Entomophaga aulicae [is a natural adversary]. Once it takes hold, it can wipe out entire caterpillar colonies. But the fungus needs cool, wet springs to thrive. And Maine, which is located in the fastest-warming region in the lower 48 states, has experienced warm springs in the past few years.
More info at The Atlantic.