As I have been traveling all over the state this spring, I've noticed a few tent caterpillars and webs on trees. Two nights ago, I noticed a large mourning cloak caterpillar and thought I might put up a reminder about these different species.
Here's a sample of a bush that I found last week that is covered in webs of the eastern tent caterpillar. These emerge from eggs and the caterpillars form a tent in the crotch on a branch.
The caterpillars leave en masse from the tent to feed and then return to digest. The tent serves as some predator protection and also as a green house to keep the caterpillars warm and aid in digestion. I like to watch these tents during migration, sometimes you can find a yellow-billed cuckoo or black-billed cuckoo tearing in to one and gorging on the ample food source.
When the hundreds leave the tent to feed, you might see them crawling all over on the ground. These two were on one of the walkways at Jeffers Petroglyphs, but I saw quite a few eastern tent caterpillars along the Minneapolis Greenway on Saturday...not faring too well either with the number of riders that were out.
This is a photo from the Vermont Division of Forestry of a cluster of forest tent caterpillars...which do not spin a tent like the eastern tent caterpillars do. They do make a silky sheet to molt under, but according to my Caterpillars of Eastern North America they do not make the tent and use their silk the same way that eastern tent caterpillars do. They do have a tendency to cluster on the side of a tree and could fool people into thinking they are mourning cloak caterpillars.
These are mourning cloak caterpillars that I gathered on the bike trail last summer. The female butterfly lays eggs en masse on the host tree and the caterpillars feed in a large cluster as they grow. When it's time to pupate, large groups will exit the tree--resembling the tent caterpillars. Last year, when I posted my photos, some people commented and emailed me that they had those and were told they were tent caterpillars or gypsy moths and that they should be exterminated. These guys might eat all the leaves off a branch but they will not strip a whole tree. Plus, they turn into gorgeous butterflies (that hibernate over winter--how cool is that). Also, these guys do not make tents, they do not leave a silk trail or make a silk sheet for molting.
People tend not to care for tent caterpillars because of the caterpillars can reduce the growth their host trees. I'm ambivalent about them--they are a great source of food for wild birds. But many understandably call exterminators to deal with tent caterpillars. Make sure you know your caterpillars before you call your exterminator. Not all exterminators seem to know their caterpillars. If you see red spots on the back of the caterpillar and it has a "spikey" look, that could be a mourning cloak.