Caterpillar Webs!

I noticed these webs in a tree behind my kids' preschool and was very intrigued.  When we think of webs, we think spiders, but these are actually webs from caterpillars.  There are several kinds of caterpillars that create web-like nests in trees.  The most common in our area are the eastern tent caterpillar and fall webworm.  I believe the webs I observed are from the fall webworm.

Eastern tent caterpillars typically build their silken "nests" in the fork of branches and are seen in the spring and early summer.  Fall webworms, on the other hand, build their webs around the end of branches and are most common in August and September.  Sometimes multiple generations occur each year, in which case the earlier generation may be seen closer to June.

Fall webworms overwinter in cocoons as pupae beneath soil debris or just under the soil surface.  Once the larvae hatch and build their web nest, they remain within the web mass during development.  Once the leaves inside the web have been consumed, the caterpillars expand the web to enclose new foliage.  Webs of mature caterpillars may be 2-3 feet long.  Full grown caterpillars are only 1 to 1 1/4 inches long.  Multiple colonies can also be found in the same tree.  The nests shelter the caterpillars from rain and protect them from predators and parasites.  As their development comes to completion, they will leave the nest and seek shelter under plant debris or soil.  Here they will spin a loose cocoon in which they pupate.

There are two species of fall webworm: redheaded and blackheaded.  As the names suggest, one has a red head while the other has a black head.  Both are hairy and have a yellowish to gray body.  These caterpillars use a wide variety of host plants-almost any deciduous tree will do.  Some of the most common, however, are fruit trees, mulberry, hickory, walnut, and elm.



photo courtesy of hyg.ipm.illinois.edu

photo courtesy of G.Keith Douce, University of Georgia; caes.uga.edu

So, what do these caterpillars become?  They are moths and are mostly white in color, sometimes having black or brown spots on the forewings.  The spotted moths are more common in the South, while northern states often have only solid white moths.   



photos courtesy of Biodiversity & Ecosystem Risk Assessment; wikipedia.org