Hot, tired and hungry, I stopped at my local grocery store for a sandwich to take home. Parking in the coveted spot under a tortured live oak tree (Quercus virginiana), I saw something I had been looking to take pictures of for decades: The poor tree (growing in one of those small parking lot islands without enough soil or space for the roots to spread and the tree to reach its full potential) was literally covered with a silvery-white silken web.
A spectacular (if not spooky) sight, nearly this entire tree is covered in webbing – done by the work of a group of insects known as tree cattle, bark lice or psocids.
Photo Credit: Carol Cloud Bailey
Believe it or not, the web and its 6-legged creators do no damage to the tree.
Photo Credit: Carol Cloud Bailey
Tree cattle are common in the southeastern US in the late summer and fall and can be mistaken for spider or worm webs. Some years the critters time their web-making perfectly to provide natural Halloween decorations.
Photo Credit: Carol Cloud Bailey
Archipsocus species are the most common web-weaving psocids. These small, shy insects are hard to find under the webs, but occasionally the herd or a single specimen can be found upon close inspection.
Photo Credit: Carol Cloud Bailey
As incredible as these large webs are, they rarely last more than a few days.
Photo Credit: Carol Cloud Bailey
Tree cattle were at work!
Also known as bark lice or psocids, these interesting insects were one of the first subjects presented in a question to me as a young horticulturist right out of college. At that time, it required a bit of investigation to find the answer for the client. Over the years, I have talked about and observed tree cattle many times, but it seemed fate worked against me and I never had a camera in hand to take pictures when these creatures were at work.
This time, my trusty new Nikon was in the car. (Yippy!)
So out came the camera, and I started snapping away. Of course, in a grocery store parking lot, folks wandered over, wondering what I was up to. (You can’t call many Floridians shy.) Some wanted to tell me all about the webbing. Others asked questions, which I was happy to answer.
Why all the hoopla? Tree cattle are a spectacular occurrence – once you see one of the webs, you won’t forget it. Under that webbing is a “herd” of insects that belong to the Order: Psocoptera (the “P” is silent). There are many insect species in this group, but the ones that live on trees and other plants all have something in common: They’re harmless to the plants they live on. In this parking lot tree’s case, the most likely candidate for the web was Archipsocus nomas, which is native to the Gulf States.
It seems there’s a species of psocids present in just about all regions of the US. Some live on shrubs, others on trees. (It seems they stick to woody plants, but I haven’t seen any real research as to what species are favored. I have seen them on citrus, oak, crape myrtle and hickory, and in my area, I suspect they prefer species that also harbor lichens.) Some spin a communal web that closely covers the bark of the tree, like the ones I found. Others simply congregate in large groups and move about the plant in herds.
Tree cattle are true insects with six legs. Their life cycle is simple or incomplete metamorphosis. The eggs hatch into small insects that molt through stages, getting larger with each new skin. The adults are small, usually less than ¼ an inch long, and are often dark-colored, though some are striped or marked with yellow or white. Under the microscope, a characteristic bump on the head is visible, as are the chewing jaws. It’s usually in the juvenile stages when the insects gather in large herds.
Despite their large webs, these critters are actually the cleanup crew: They feed on fungi, algae, lichens and dead plant and animal debris. No one’s really sure if they’re “beneficial,” but we do know they’re not harmful to landscape or garden plants. Their populations can reach “gang” size anytime of year, but they’re more common from spring through fall.
Here in the southeastern US, several species are gregarious when immature and come together for the common good. When in this stage they build huge webs – probably for protection. I’ve actually seen some webs spread from the base to the top of 60-foot-tall hickory trees! They were so spectacular, they stopped traffic. Of course, when this occurs many gardeners panic, thinking the infestation is similar to webworms, which are very destructive. However, with a brief inspection, it’s quite easy to tell the difference between tree cattle webs and webworms – tree cattle webs do not encompass the leaves.
All in all, tree cattle are interesting, often jaw-dropping sights. If you see one of their web masterpieces in your yard, don’t panic: No control or intervention is required. As incredible as these large webs are, they rarely last more than a few days. (Some entomologists claim the psocids eat the web when they’re finished; others say it weathers away.) Once the tree cattle have matured to adults, they seem to disperse – much like humans who hang out in gangs in the mall as teenagers only to drift apart as grownups. Predators like birds and other insects reduce populations; frost and cool weather also kill a few. In the end, psocids go about life mating and lying eggs and doing no harm; they’re so small, few folks even notice them hanging out on trees or in the debris.
Despite tree cattle innocence, some gardeners find their webs objectionable. But like a trip to have your teeth cleaned, just grin and bear it. There’s really no effective way to remove the webbing, and it’ll be gone on its own anyway.
These insects are present naturally throughout their native range and will find a home on any number of plant species. Like hurricanes and shortening days, psocids are just part of what’s natural. There’s no way to avoid them, and the webbing doesn’t appear every year (usually). So if tree cattle grace your place (or trees) this year, try to marvel at their uniqueness – and enjoy the wonder of nature’s diversity.
