A reader recently asked us a simple question: “what is wrong with my tree?” She explained that her tree is covered with webs from “end to end,” and she sent a photo that shows the problem. (The photo of the web-covered tree is below.) The reader made no mention of worms, caterpillars, or other creatures, although we presume that she thinks that some worm or insect is responsible for the webs in her tree, or else she wouldn’t have written to us with her question. As it turns out, there are several types of caterpillars that build webs in trees, and we are more or less certain this is the issue our reader is dealing with. Nothing is necessarily “wrong” with her tree – it just appears to be overrun with caterpillars that spin webs.
First, to get an idea of our reader’s situation, check out the picture she sent in:
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Unfortunately, the image is blurry and a bit small, but you can still see pretty clearly that her tree is covered in webs. As we said, this is almost certainly the work of caterpillars, and perhaps this is all our reader wants to know. However, there are something like 175,000 species of caterpillars, so saying “it was caterpillars” isn’t a particularly precise answer, and we’ll strive for greater specificity. On the other hand, with so many different types of caterpillars, it becomes hard to identify any exact species, particularly when we can only look at the webs the caterpillars spun, and not the caterpillars themselves. Thus, we will aim for something in between, listing some of the common caterpillars that build webs in trees, while not definitively committing to the species she is dealing with.
Only a small percentage of caterpillars spin webs, so it is not as if our reader could be dealing with any one of 175,000 species. Rather, she is dealing with something like fall webworms, inchworms, or tent caterpillars. Of these, only the fall webworm is an exact species (Hyphantria cunea), and this also happens to be one of the caterpillars that probably isn’t effecting her tree. Although they spin webs that look like the webs on our reader’s tree, fall webworms, as their name implies, generally come out in the fall and spin their webs. (They also come out in the late summer.) Given that the reader submitted her question recently, in late spring, she probably isn’t dealing with fall webworms.
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“Inchworm” is very vague term that refers to the larval form of geometer moths, of which there are about 35,000 species. Some people stretch the word inchworm to include even more types of caterpillars, including tent caterpillars, but this makes an imprecise word even more imprecise. Tent caterpillars belong to the Lasiocampidae family and inchworms to the Geometridae family; our usage will so reflect. Some types of inchworms produce simple webs, but these are basically threads that inchworms use to attach themselves to trees, and thus don’t seem to be exactly what our reader is dealing with.
This leaves us with tent caterpillars, which take their name from the fact that they build “tents,” or webs. There are a little over 20 species of tent caterpillars, and six live in North America, so there aren’t nearly as many tent caterpillars as there are inchworms. By far the best known tent caterpillar is the Eastern Tent Caterpillar, whose webs start to become visible in April and grow larger over the spring. For this reason, we think it is most likely our reader is dealing with Eastern Tent Caterpillars, or at least some species of tent caterpillar, although we can’t be certain of this. The seasonal cycle of the Eastern Tent Caterpillar fits with the experience of our reader, but they also tend to make one large nest, whereas other species make several smaller webs, and this latter practice seems to be more consistent with what is pictured above, a tree covered from “end to end.”
We aren’t certain what species of caterpillar our reader found, but we are pretty certain that the webs in her tree were or are being built by caterpillars. The reader technically asked what was “wrong” with her tree, but not all caterpillar infestations cause much damage. Eastern Tent Caterpillars, perhaps the most likely suggestion we offered above, don’t cause any damage beyond temporary defoliation. Once the caterpillars are gone, the tree will grow new leaves. As any tree lover knows, not all caterpillars are so innocuous, and we don’t want to give her a false sense of hope, but it is worth mentioning just the same. Our reader’s exact question concerned what was wrong with her tree, so we want to conclude by saying nothing may be wrong at all.