Sometimes we write articles about the weird and unusual samples we receive as reminders of the beauty, wonder, and variety of events in the natural world. A second reason for articles about the bizarre is a historical record so that on some future day, we’ll have an answer to the common question, “Didn’t we see this once before?” The next time someone asks about walnut trees shrouded with what looks like silvery cellophane, please think of this article.
This summer, we had two inquiries from western Iowa (Fremont and Harrison Counties) about “silken tree wrap.” Both happened to be defoliated or sparsely leafed walnut trees. Our diagnosis, awaiting specimens for confirmation, is that the tree wrap is the work of webbing barklice. Barklice are not lice; they are members of an order of insects called the psocids (the “p” is silent). Psocids are small (most species are about 1/8 inch long) and harmless. They live on tree bark (obviously) and rocks where they feed on lichens.
Some species of barklice, under some circumstances, shroud the tree with silk, possibly for protection and to maintain humidity. It’s an interesting phenomenon that I hope to see in person someday.
Here are several articles on the topic of webbing barklice:
Webbing barklice did not eat the leaves or cause the sparse foliage on the wrapped walnut trees. I suspect it is the other way around. The wrapped trees appear to be isolated and out in the open, and the sparse foliage would make the trunk a hot, dry place. The barklice might have wrapped the tree as protection from desiccation during the heat and drought of June. Neither the barklice nor the webbing will be harmful to the tree, and treatment is not necessary.
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