I've been seeing these too. I'm not for sure what they are but I believe they are called bag worms. Do you have fruit trees? They tend to make their home in trees in a bag till they come to life. Then they are all over the place. Again I'm not really sure.

Pretty fuzzy photo, but from the blue lines along the side, it looks like the Forest Tent Caterpillar to me. Kind of a misnomer, in my opinion, as they don't spin a big, conspicuous 'tent' like the Eastern Tent Caterpillar.
I've been battling FTCs for several years - they appear just about the time the young oaks planted along my driveway are about halfway leafed out, and can totally defoliate an 8 ft tree overnight. Almost seems like they crawl up the trunk at dusk, eat all night, then crawl back down to hide, as I rarely see the caterpillars - just walk out to find a naked tree(or trees).

Here is a bit of trivia: there is only one known carnivorous caterpilllar in the world, and it lives in Hawaii. The rest all eat plants.
I have these guys, too. I pull them off the plants when I see them and toss them into the grass. I just can't bear to kill a caterpillar. But I hope a bird will eat them:)
Bob

I thought these were bag worms but I think the Tent Caterpillar is more accurate. I've been pulling them off my plants for days now. They are eating the very tasty leaves of my weeping cherry, hostas, and roses. They've even left a telltale mess of waste product behind. Under my roses are tiny little black pellets about the size of a pencil lead.

CONFIRMING.. tent caterpillar, YUP! STOMP HIM or HER! They STRIP young trees here in SE Ohio.
We take a burning torch to 'em if their webby-nests can be reached well in trees.

Hate em! And I'm kind hearted too!
homegrown

We have them in our wild cherry tree. They don't bother anything else, and though the "tents" they make are ugly and there's thousands of them on the tree (a few are cute, thousands are just icky), they never seem to do any major damage to the tree. In a few weeks you'll have a bunch of mid-sized yellow moths fluttering around.

So...whether it's a good or bad caterpillar is a matter of opinion. If the damage is minimal, I happen to think a few nibbled leaves is a minor exchange for pretty fluttering things later. My kids, who think the little furry caterpillars are fun to play with, would agree.

Those are tent catepillars that make the big ugly nests you have to burn off the trees- I picked them all off and got a spray at Natorps to keep them off- yuck- Ai love butterflies-but you get uglt little brown moths from these and a big ugly mess

fennelgrl,
There are products that will take out any plant-chewing caterpillar. One is called BT, a natural product made by fermenting bacteria (Bacillus thuringiensis.) It doesnÂt last too long though.
Another is also made by fermenting bacteria, (Saccharopolyspora spinosa) and this one is very effective. I used it three years ago with a massive invasion of tent caterpillar and southern tent caterpillars. They disappeared in about three days, dead bodies hanging in their tents and on the ground.
It works by making them unable to eat anything. I havenÂt seen any of these caterpillars in the past two years. Gardens Alive will have this product under the name of Bulls-Eye Bioinsecticide. At least, this one seems to work and lasts for a longer period of time.

Here is a link that might be useful: Gardens Alive