Photo by Nathan Riggs

Mysterious Webs Adorning the Trunks of Local Trees By Nathan Riggs

Photo by Nathan Riggs

Many local nurseries as well as the Bexar County Extension office have fielded calls over the past couple of months regarding strange "webworms" that were building webs on the trunks of their trees. Webworms? On the trunks of trees? That certainly would be something–that is if it were true! Fortunately, there is an answer for this strange phenomenon that has a happy ending.

Just to clarify, webworms build silken webs over leaves and vegetation on trees. They feed on the leaves within the web and expand the web as they need more food. The web also serves as protection from rain, wind and predators such as birds and wasps.

Since these webs are appearing on the trunks and limbs of the tree and not the leaves, we are probably –make that definitely–not talking about those nasty webworms. What are we talking about then? We are describing the webs made by Archipsocus nomas, the webbing bark louse.

Bark lice are small, brown insects that live on the rough bark of hardwood trees, especially live oak trees. Contrary to their name, bark lice are not parasitic on humans or animals, rather they live on the bark of trees, feeding on fungi, lichens and dead insects. They serve as "clean-up" crew of sorts for the tree. They do not eat leaves or bore into the tree, or consume the bark of the tree. Because they are small and vulnerable, bark lice have developed a protective means for their survival: silken webs. Seemingly overnight, a colony of bark lice can envelop the trunk of a large tree with a silken covering. This silk covering affords bark lice the protection from predators while they feed underneath.

Many callers are concerned that the silken covering on the trunk and limbs will smother the tree. Rest assured that this will not occur. Trees transpire, or breathe, through minute openings called stomata on the underside of their leaves. Since the webs are not covering the leaves, smothering does not occur. Since silk allows air to pass through, it is doubtful that smothering would even take place.

Officially speaking, treating bark lice is not necessary because they cause no harm. Some homeowners think they are unsightly and wish them to be gone. If treatment is absolutely desired, there are some options available. One option is soapy water. A concentration of 2 tablespoons of liquid dish soap per gallon of water will affect bark lice. Removing the webs with a stream of water by itself will not kill the bark lice, but it will stimulate them to rebuild the webs within a few hours. Insecticide sprays to the trunk will control these insects as well.

Having said all of this, the fact remains that bark lice are mysterious and unusual South Texas residents that appear during summer months. Their webs conjure visions of destruction brought upon by webworms and all of the heartburn associated with their presence. The good thing is that bark lice are nothing more than Mother Nature's cleaning crew, keeping the bark on our local oak populations clean and tidy. How refreshing!

This article was written by Nathan Riggs, Extension Agent-IPM, Bexar County.

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