Are these things harmful to the trees?

The other day I had the dogs outside walking them around the house. I noticed in one of our trees in the yard, these cocoon type things. They were white and filled with what looked like dark caterpillars in them. It looked like it was trying to break open. I was wondering if they were harmful to the tree and if they should just be left alone?

Sounds like tent caterpillars. I noticed one tent on one of my cherry trees the other day. The caterpillars eat leaves on the tree and eventually turn into some type of moth. From what the agricultural people around here (Ky) say it’s unlikely they will actually kill a tree even if they strip all the leaves. They may stunt its growth somewhat though. You can knock the tents off the tree and squish the caterpillars to get rid of them. Burning them off is not recommended.

On a related sidenote, we had an outbreak a couple of springs ago of tent caterpillars here in the bluegrass that you wouldn’t believe. There were masses of the things climbing on the fence and brick walls of my house. Ugh. At the same time there was a huge increase in mares losing foals, before and after birth. Some researchers here believe the two were connected although no one has yet shown a clear cause for the foal die-off. Horse farms lost millions in yearling sales because of it.

Here’s a bit more info on tent caterpillars.

Tent caterpillars can be a problem. There are several different types in the US. Control measures vary with type and location.