Bug Nests in Black Walnut Tree

Asked July 20, 2015, 9:16 PM EDT

We have a 130 year old Black Walnut Tree (very, very large) and it has been dropping a lot of leaves lately. We found at least 3 of these large bug nests (worms, caterpillars??) in the tree. We are worried that this could harm the tree and not sure how to get rid of these or what they are. We do not want to damage the tree or spread them. Can you help? We live in Canby, OR

Clackamas County Oregon black walnut tree horticulture

3 Responses

My guess is that the “nests” you see are formed by fall webworms. If so, they are considered occasional pests which won’t cause long term damage. They form large silken tents filled with caterpillars, frass and dead leaves, which may eventually enclose entire branches.

Fall webworms are pale greenish or yellow with dark stripe down the back and a yellow stripe along the sides. They also have long silky hairs which arise from yellow and black tubercles (small bumps) on their body. If the nests are within reach, you can disrupt them, perhaps using a pole or a powerful blast from a hose. Don’t burn them because that might start unintended fires in houses, sheds, barns, or fields.

Let’s confirm the identity of the nests. To do so, reply to me and attach at least 2 more images: one of the tree overall, and another of a large portion of the tree with one or more nests.





Thanks so much for your reply. I have attached 3 images. One of the tree, you can see the size in relation to the house. We just movehttps://ask.extension.org/questions/263581#view-response-296990d in here and also have a question about whether we should have this tree trimmed as it is so large and some of the branches are close to the house. When is the best time to prune a tree like this? Do you have any recommendations of local companies who know how to approach a 130 year old tree., I would hate to have any damage done as it is a beautiful old tree that has been here since this land was homesteaded. With regard to the bugs, I have attached a close up of the bugs that I took as well as one of the nest. There are little black things that look like they could be eggs all over the nest as well. There are several nests in the tree but they are not close together so it is not possible to get pic of several nests at the same time as the tree is so large. Thanks again for your help!

Wow! What an amazing tree. Those bugs aren’t a threat. They are fall webworms, the little black things in the webbing is excrement.

For pruning, I suggest you contact a Certified Arborist, a person who can obtain that title only by passing an exam and, then, continuing to accumulate continuing education. Quite a few such persons work within our region. You can locate them with your zip code at http://www.treesaregood.org/findanarborist/arboristsearch.aspx. Before you hire someone, discuss the details with several persons who come out for an onsite evaluation.