Caterpillars That Build Big Nests: Tent Caterpillars and Webworms

Tent caterpillars are common in Spring

Tent 1

 

 

 

 

By April, numerous webs are noticeable wherever the native Eastern Tent Caterpillar (Malacosoma americanum) is common. This caterpillar nests communally in a silken tent built in the crotch of small fruit-bearing trees - most notably the Black Cherry (Prunus serotina). The group usually represents a family of siblings that hatched from one batch of eggs, although two groups may join and form a larger tent.  

 

 

The species survived the winter as batches of eggs (numbering 100-400). An egg mass typically is laid as a ring around a small branch, and looks like brownish to grayish hardened foam covered by a coat of varnish. Eggs hatch in the spring while leaves are beginning to grow on the trees.  

Tent Caterpillar Eggs1 fg
Tent Caterpillars Best

 

 

 

 

The caterpillars are hairy and black with a white stripe down the back. A series of blue dots run along the orange-speckled sides. Young caterpillars forage on leaves and begin to spin a “tent” from a gland located in the head. Throughout the larval stage, the caterpillars cluster for protection within the tent when not feeding, during the heat of the day, or during bad weather.

 

 

 

 

As the caterpillars grow, the tent also must be enlarged. This makes the growing tent appear to have layers. When matured within about six weeks, caterpillars may be as long as 6.5 cm (2.5 inches). The insect pupates within individual cocoons.

Tent Layers
Eastern Tent Caterpillar Moth

Adult moths emerge about July, mate, and then lay eggs to repeat the cycle. Fore-wings of adults are warm brown with a darker cross-band lightly outlined above and below.
 

 

Tent caterpillars are not a danger. Although enough tent caterpillars can defoliate a small tree, the tree will grow a second batch of leaves if it is not compromised by other diseases or stresses. However, the tree may not grow as much as it would have without the pests present. Because no new eggs will be hatched on the tree that season, those leaves will remain.  Some people try to get rid of the tents by burning them, but this is not recommended due to the fire hazard. Preventative approaches include removal of egg masses before they hatch in the spring, or physically removal of the tent when most of the caterpillars are within it.
 

During summer and early fall, many hardwood trees including oak, hickory, ash, and maple have silky webs covering the tips of some branches, unlike the webs seen in the spring which are made along the forks of branches by a different caterpillar. The web may look like cotton candy you might buy at a carnival. The leaves inside the web turn brown or appear to be eaten away entirely. The dark spot at the bottom of the web is a collection of a large number of pinhead-sized fecal droppings from the caterpillars (the web is tight enough that even they can’t fall through).

Closer study shows the web to be made of a large mass of long fibers spun by caterpillars of one of two species: the Oak Webworm or the Fall Webworm. These larvae enlarge the web as they grow to encompass more food. If you disturb the web, you can see the caterpillars make jerking motions all in unison. 

Web 1
Worm Cluster 1

 

 

 

 

If you try to pull the web apart, you can see how difficult it would be for a bird or predatory insect to get at the juicy caterpillars that crawl about inside the web. Still, some birds, wasps (especially yellow jackets and paper wasps), predatory stink bugs and parasitic species of flies and wasps are among the predators that feed on them.

 

 

 

The caterpillars are not very colorful, and they are covered in long hairs attached to each segment. Large numbers of these caterpillars can defoliate a tree by encompassing so many branches that the tree becomes a massive collection of webs, but small numbers seldom cause much damage to the tree. Removal of the webs, or branches with webs, can help reduce the unsightly appearance on shrubs around homes.  

Single Worm

The adult moth has a pattern on the white fore-wings that varies from no spots to heavy grayish-brown spotting. One to two blackish spots occur on the hind-wings.  

 
 
 
 
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