Name: Pam V.
Date: Tuesday, May 07, 2002
I've checked your biology section but cannot find this
problem. We are new to Illinois and all of a sudden our trees (does not
seem to matter what kind) have what looks like dense spider webs in
them. The webs are crawling with caterpillar-like bugs. Is this
dangerous to our trees? Will they go away by themselves?
Sounds like "tent caterpillars". I suggest you cut the webs off and either
burn them or dispose of them...but not in you yard compost a wooded area
where they will continue their life cycle.
Peter Faletra Ph.D.
Office of Science
Department of Energy
These are probably "tent caterpillars", which build their "tent" in
the fork of a tree branch. They are voracious eaters and can defoliate a
tree or ornamental shrub very quickly. I do not know if they are lethal to
the tree/shrub, but certainly don't do them any good. There is a similar
caterpillar (forgot the name) which is similar except they build their
"tents" ON a branch and not in the FORK of a branch. You can find out a lot
on the internet search the term: "tent caterpillar". I use the search engine
www.google.com . You can find a photo on the site:
I think that physical removal plus an insecticide is recommended because the
insecticide alone cannot penetrate the "tent".
At this time of the year it likely you have one of the
tent caterpillars. The easiest method of control is
to go out at dusk with a glove and plastic bag and
physically pull the tent from the tree (be careful to
keep as many of the insects as possible, and place the
tent into the plastic bag. You can then tie the bag
closed and place it in the trash.
I have seen people do all sorts of crazy things, from
burning the tent (and killing the branch) or cutting
off entire branches. Sometimes the humans do more
damage than the insects would. The method I suggest
is safe for the humans and tree involved. Pruning off
the affected branches is an option of the tent cannot
be easily removed. Close to the ground you can use a
hand pruner; stores like Home Depot sell pole pruners
for out of reach pruning. As always do not use a
pruner anywhere near electrical lines and be sure to
maintain proper safety while using a ladder.
I you do not remove the tent, the caterpillars will
leave the tent during daylight and eat leaves on
adjacent branches. The caterpillars and tent will
grow in size, and you will find waste matter from the
insects inside the tent. I don't think one
defoliation will kill the affected branch unless the
tree is already weakened. This certainly is a
visually unpleasant problem which as I mentioned is
safely, easily rectified.
For more information contact your county local
agricultural extension agent. Check the government
listings of your phone book. Good luck!
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Update: June 2012