Tent Caterpillar Frequently Asked Questions

We have received numerous call regarding the tent caterpillar infestation in our area. The following is a Q&A session regarding these pests:

1. Why did we only treat the ornamental trees for tent caterpillars?

We paid for the installation and maintenance of ornamental trees in Silver Firs II, and need to protect their beauty. The trees affected this year are "wild" trees, mostly Alders, in the common areas and NGPAs. Most experts do not recommend spraying wild areas.

2. Will the (now emerged) caterpillars damage the common area trees?

The caterpillars are now at the stage that they should do minimal damage to trees. Tent caterpillars are mainly a nuisance pest; rarely do the trees die.

3. Should we treat the caterpillars now? Why?

It would not be cost effective to treat the caterpillars now. The best treatment is a biological insecticide, Bacillus thuringiensis (B.t) which the newly emerged caterpillars eat off the leaves. This bio-insecticide is relatively safe for beneficial insects and animals. Since the caterpillars are at their current (later) development stage, they are not eating much, and applying the bioagent would do little good. Applying other chemical agents harm good insects, and is not recommended.

The recommendation at this point is to physically remove the tents from the trees (either stripping them off, or cutting off the affected branch area) and discarding in a plastic bag into the trash. If you wish to do so, please make sure the trash bag has most of the air out, and seal the bag as tightly as possible before discarding. Tent caterpillars are in the "tents" in the evening and early morning hours. It is at this time that it would be best to cut off the tent, and dispose of it (to get the most caterpillars). However, any time that the tents can be disposed of would be greatly appreciated.

4. Is there anything we should do to prevent a tent caterpillar problem next spring?

We will certainly spray to prevent tent caterpillars in our ornamental trees along the roadsides. As for the rest of the common areas, the job would be massive and prohibitively expensive. Many of the trees in the common areas exceed 100 feet. As well, keep in mind that even though these areas are common areas, they are still considered wetlands, and require a special permit to spray. The common feeling is that we should spend our money controlling pests in the landscaped areas only.

Tent caterpillars, of course, turn into moths. The good news is that they are great food for the birds!

For more information on tent caterpillars, please go to http://gardening.wsu.edu/library/inse003/inse003.htm.