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Sunday, July 4, 2010

Sycamore tussock moth caterpillars

Sycamore tussock moth caterpillars, Halysidota harrisii, are falling out of the trees in New York City this week. This one is crossing paths with a tiny red spider mite. 

I keep finding sycamore tussock moth caterpillars on low stone walls in Manhattan’s Central Park and on the iron fences that surround the lawns of the American Museum of Natural History. 

The caterpillars are covered with white hairs. They have four orange tufts and four white tufts on the front end and a pair of white tufts on the rear. They will eventually grow to be relatively unremarkable yellow moths with pale bands on their wings.

Each time I find one of the caterpillars I look up and see either a London plane tree or an American sycamore – their host plants.

 American sycamores and London plane trees are easily recognized by bark that peels off to leave puzzle-piece patterns of green, cream, and brown on trunk and branches

Like many insects, sycamore tussock moth caterpillars eat just a few related plants -- sycamores and plane trees -- and have ended up being named after their food. They eat the soft green leaf tissue and leave behind lacy leaf skeletons made of stems and veins.

Sycamore tussock moths spend the winter in cocoons on host trees. Adult moths emerge in spring. They mate and then lay eggs under leaves and on bark. The eggs soon hatch into a profusion of fancy white caterpillars. By June,  there are so many caterpillars that we notice them falling out of the trees and walking along fences.

The caterpillars we are seeing in Manhattan now will soon make cocoons. They’ll emerge as adult moths in late July and August to mate and lay eggs that will hatch into a second wave of caterpillars at summer’s end. Those caterpillars will make cocoons in September or October and spend the winter inside them -- emerging as adults next spring to begin the cycle again.

There is more information about urban moths and butterflies in my book, A Field Guide to Urban Wildlife of North America, which will be published by Stackpole Books in spring 2011. 


  1. Dear Julie: I would like to use one of your photos to show family and friends online. One of these attractive critters landed on my shoulder two weeks ago, stunk or spiked me (I retrieved the body to identify it), and I and a significant and painful allergic reaction.
    With your permission and correct information, I will attribute the photo as you direct.

    1. Sorry to hear that! Attribute to J. Feinstein and include a link to my blog so they can read about it.Best, Julie

      This is the link:

  2. They sting the heck out of you,, I hate them.

    1. They do sting, as do many caterpillars that are spiked and tufted with irritating hairs -- it is a good rule of thumb never to touch a fancy looking caterpillar unless you recognize it as benign. The stinging is defensive, not aggressive, but sometimes these fall out of trees and surprise themselves and the person they fall on with bad outcome.

  3. I just saw one of these cute bugs move swiftly across the ground onto a sycamore tree and quickly up the trunk. Luckily I didn't touch it.

    1. Good looking aren't they? Just keep your hands off 'em…