What Are Those Spooky Web-Looking Things on Tree Branches?
This last month has seen ghostly webbing on many Kansas trees.
Halloween may be approaching but this is no spooky spider webbing.
It is merely the work of “webworms”...the larvae of moths that are just trying to “make a living” on the wide variety of hardwoods found in our towns and eastern Kansas forests.
These webworms of fall are not really a threat to our healthy trees as much as they are an aesthetic challenge to our well-groomed yards.
But before we call the commercial tree services to haul away these gossamer branches, we ought to see the world as a caterpillars sees it.
And when your diet is tree leaves, that leaves you out-on-a-limb...with birds.
And what do birds eat? Caterpillars!
So what is a poor caterpillar to do?
Well, there are whole bunch of butterfly and moth larvae that face this dilemma.
Some species just produce huge numbers of delicious young and hope some survive...sort of trick-or-treat for birds.
Another strategy is to lay low...and blend in. You can camouflage yourself by resembling wood or a green twig, or even the leaf. But that is not enough. If you keep crawling when a bird lands beside you, even a birdbrain will still see you as food. You have to straighten out, like a stem or leaf, and remain perfectly motionless. So camouflage takes energy, to produce the pattern and to produce the behavior.
On the other hand, you can invest your defensive energy into producing toxic chemicals.
Load your body with terrible tasting molecules that can gag a magpie. In this case, the first caterpillar a bird tastes loses its life teaching the bird a lesson. But then, instead of being camouflaged, you need to stand out in bright colors, advertising that you are also bad tasting. Toxic chemicals and bright patterns...they also take energy to build.
So what do we see in the webworm? While spiders have silk glands in their tails, caterpillars spin silk with their mouthparts to make a cocoon. That is how the silkworm makes silk. And that is how these webworms encase a branch.
If you stay inside the webbing, you don’t have to be camouflaged or produce toxic chemicals or freeze in place. And it is harder for the bird to see you, and a bird doesn’t want to get all “web-sticky” anyway.
I speak as if these webworms are making a conscious decision on strategy; but of course their little webworm brains are not up to that. It has been natural selection over many thousands of years that has led these caterpillars to making webs before making cocoons. Just like we built log cabins to keep our predators away, they have used these webs for protection.
And now, most have dropped to the ground to overwinter.
Perhaps, before the webbing weathers away, you can clip off the webbed branch and use it as an outdoor decoration for Halloween. If you don’t know the biology, it might still be spooky.