A flowering crab tree in my yard has been infested with some kind of worm or caterpillar that is black with two light stripes running its length. The worms are emerging from a large silky cocoon-like nest that has been weaved at the base of an upper branch.

Can anyone suggest what kind of insect builds such a nest, and how to eradicate the infestation?

Agor, those are tent caterpillars. Their production runs in cycles. Very destructive to the foliage. I can't stand them. They killed a beautiful plum tree of mine. Since they have already emerged, the best defense is to call a local tree expert or landscaper. There are both pesticides and natural microbial insecticide that can be used. That is your call. With the microbial insecticide, they will have to spray the trees on a regular basis. The caterpillars bring it with them back into the "nest." It takes a while to eradicate them but it will eventually stop them.

Here are some links to more in depth information about them and controlling them:

Forest Tent Caterpillar (http://www.na.fs.fed.us/spfo/pubs/fidls/ftc/tentcat.htm)
Eastern and Forest Tent Caterpillars and Their Control, HYG-2022-95 (http://ohioline.osu.edu/hyg-fact/2000/2022.html)
Tent Caterpillar (http://www.tent-caterpillar.com/)

It's important to know what geographic area you live in... what type of weather you've been having and... you never know... the critters that are growing in your yard may be the ones that are keeping the "pests" you normally have, in check.

LOL, Kstar. :) Thank you for the thumbs up. Agor gave an excellent description of the "worm". There was no doubt in my mind that he/she is dealing with tent caterpillars. I have enough experience with those little creatures. They love fruit trees and I have plenty of them. You are right, about the area. I didn't know which one, but I suspect it is the Eastern Tent caterpillar because the stripes are so clear to Agor. They are my arch enemy this time of year! Hate those little buggers. They kill off the fruit that I use to feed the moose and deer. I have just been out clearing a couple of my trees of those cocoon nests. I try to kill the eggs before they have a chance to start their nest. The ones I can't reach, that are too high up, do manage to do their thing and hatch. They don't serve any useful purpose except to feed the birds when they hatch and the bats when they mature. They turn into moths. So, I don't use pesticides. I try to use all natural products to keep all the nuisance "insects" in check. I have enough flying insects, and plants that produce food, so the wildlife is very well fed around here. So, no worries about throwing out the natural balance. That is really important to me.

Thank you, Ruby. With your help, I easily identified the pests as Eastern Tent Caterpillars. I removed the nests before the worms could do anymore damage to my crab tree. They had already defoliated one limb.

I agree with you that there are plenty of other insects in my region (south-central MN) to do the job of pollination: bees, butterflies, etc. I prefer to have fruit in the crab tree because the birds and squirrels feed on it during the cold winter months.

You are welcome Agor. Tent caterpillars serve no useful purpose. They don't pollinate anything. So feel free to destroy the nests. If you do any kind of limb trimming in the late fall/winter, that is the time to check for the eggs and kill them. Just use a gloved hand and squash them with your gloved fingers. It is the best and easiest way to control them. Since you were able to catch them early enough, next year, the foliage should grow back on that limb. If it doesn't, the following fall/winter, cut the limb off. Don't do it now. Trees should be pruned when they are dormant. Late fall through very early spring is a safe time. Don't cut it flush to the tree. Leave about a 2 inch stump.

You are welcome Agor. Tent caterpillars serve no useful purpose. They don't pollinate anything. So feel free to destroy the nests. If you do any kind of limb trimming in the late fall/winter, that is the time to check for the eggs and kill them. Just use a gloved hand and squash them with your gloved fingers. It is the best and easiest way to control them. Since you were able to catch them early enough, next year, the foliage should grow back on that limb. If it doesn't, the following fall/winter, cut the limb off. Don't do it now. Trees should be pruned when they are dormant. Late fall through very early spring is a safe time. Don't cut it flush to the tree. Leave about a 2 inch stump.


Hey now... "tent caterpillars have no useful purpose"?? Ya know... I sure don't have any experience with those critters but I've always wondered why God gave us flies or mosquitos. I sure couldn't find any use for 'em. Then... a very wise friend of mine reminded me that without flies we would be "knee deep" in dead stuff. Flies in their larval stage as maggots (yuck) serve a very useful purpose by disposing of decaying organic things. I'm still looking for the answer for mosquitos, though.

As far as I can find from my research, I haven't found any answer as to whether the tent caterpillar serves a purpose. The only thing I can come up with, which was pretty much on my own, is they are an added food source for birds. As moths, added food source for bats. Same goes for mosquitos. That is all I can find. So, if you can come up with something else, I am all ears. In any event, I don't kill them all. I just keep the population under control around my yard. I have a huge wooded area in which I just leave them all alone to do their thing.

Bush, please look at the links. Unfortunately, they don't turn into butterflies. I wish they did. After going through the cycle of growth, eggs, then hatching into tiny wormlike creatures, then grow into caterpillars, they leave the tree nest and find any safe crevices they can to start spin their individual cocoons. They emerge in July as moths.

I live in the Southern Gulf Islands, Tent Caterpillars are very cyclic in our area. Every 7 years. The trees I wish to protect on my property, I do a thorough inspection and I find dark brown scabs (about the size of the end of your thumb) pick these off, drop in a bucket of bleach & water. When you look at these scabs you will see millions of eggs! These are tents due to hatch. The scabs pick off easily. The ones I have missed or can't reach that turn into tents, I burn with a rag at the end of an extended pole. Then to protect the tree from the emerging caterpillars, I wrap the trunks with saran wrap (about 2 feet ) and put a barrier of yellow sticky paste. I have saved my cherries/fruit trees this way.