A friend found this caterpillar while hiking in the woods on Wachusett Mountain, in Central Massachusetts, United States, in the first week of September. It was on a fallen log under the leaves of a deciduous tree, but she didn't know the exact name of the tree. She only saw one. It appeared to be just over an inch long. It was close enough to touch, but she didn't want to in case it would sting or cause skin problems.

I've never seen anything like it!

The most unusual feature is a row of four white fur-looking tufts growing out of its back not too far from the head. I used "tufts" for lack of a better word since I don't know the real term. They look like toothbrushes to me!

The body has black and yellow stripes. It has some small yellow circular areas on the black stripes.

The head is bright red with tiny black eyes. There are also a few bright red spots on the back toward the tail. The two antennae are black, and the tail is brown.

Pretty much the entire caterpillar is covered with white furry-looking spikes, including some in the front of the head that look like whiskers. There are black spikes dispersed along the body. These are longer and there are fewer of them than the white ones. There are no spikes coming out of the tufts.

What is this fascinating caterpillar? What will it grow into and when? Is it poisonous or in some way irritation to skin?

enter image description here

  • 3
    As a rule of thumb, hairy caterpillars are moths, and naked caterpillars are butterflies. – ShemSeger Oct 10 at 20:50
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    Also, moths make cocoons (pupa wrapped in a silk covering), while butterflies make a chrysalis (hard shell, no silk). loc.gov/rr/scitech/mysteries/butterflymoth.html – Andrew Jennings Oct 11 at 12:41
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    @Wigwam, and the moths use their own hair to help make their cocoons. My daughter and I caught a Tussack moth this fall and watched it make it's cocoon. If you ever see them on the ground wandering around it's because they're looking for a sheltered place to make their cocoon. As soon as we put it in a little habitat (jar with rocks and leaves) it went right to work building it's cocoon. – ShemSeger Oct 11 at 15:09
  • As a kid I remember these; there was a Linden tree along the street in Chicago that was covered with them . You couldn't walk on the sidewalk without stepping on them . The grooves in the bark would be filled with the cocoons. – blacksmith37 Oct 13 at 20:40
up vote 8 down vote accepted

That is a White Marked Tussock Moth.

The long, spiky tufts of hairs give fair warning to anyone or anything that tries to touch this species' larva. The caterpillar is covered with them and the chemicals that are transferred onto skin when touched can cause an allergic reaction in humans resulting in redness, irritation and welts.
...

It also has four tight tufts of yellowish-white hairs that look like 'pom poms' on its dorsal side near the bright red head. These hairs are barbed, making them difficult to remove from skin.

White-Marked Tussock Moth (Orgyia leucostigma)

And the grown moths look like this,

enter image description here

Source

Also see,

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