Eastern tent caterpillars are active

By Mark Halcomb

Figure 5. Forest tent caterpillar (top), eastern tent caterpillar (bottom).

Cherry, redbud, phlox, crabapple, tulips, deciduous magnolias and plums are in full bloom. Pear bloom petals did not get blown off by wind, but are now hidden by the young foliage. Dogwoods will open very soon. It really looks like spring has arrived. Once plants start to grow, insect pests and diseases are never far behind.

Eastern tent caterpillars have hatched from eggs within shiny black egg masses (Figure 1) that encircle twigs near the end of branches of wild cherry, crabapple, plum, and apple. They can also be found on peach, cherry, pear, hawthorn, and even maple.

The empty eggs can be seen in the egg masses that now appear gray (Figure 2 ). These tiny caterpillars started to emerge at bud swell (Figure 3). They usually move on the branch toward the trunk to construct a silken nest where a branch forks.

The tiny caterpillars (Figure 4) remain within the protective tent for most of the day. When temperatures are warm enough, they move out to feed on the foliage usually during the morning, early afternoon, evening, and at night. The caterpillars lay down silk trails on the bark that they follow when foraging.

The developing Eastern tent caterpillars can be identified by the white stripe down the back. As the caterpillars mature in 4-6 weeks, they can reach 2 to 2.5 inches in length. Mature caterpillars leave the tree and wander on the ground where they spin white silken cocoons on the ground in protected areas.

The forest tent caterpillar which should also be active now or very soon has white keyhole-shaped markings down the back instead of a white stripe (Figure 5). The forest tent caterpillar feeds on many types of forest trees but seems to have preferred hosts depending on the location.

Oak is the preferred host in the Mid-South although wild cherry, basswood, ash, and sweetgum are said to be common hosts. Apparently, red maple is not attacked.

Outbreaks are not common in Tennessee although in some parts of the country outbreaks lasting 3 years can reduce forest growth and 5 to 7 year outbreaks can cause high tree mortality. Forest tent caterpillars do not form a nest but instead make a silken mat on the trunk or a branch.

Fortunately, both of these caterpillars only have one generation per year.

Nurseries can remove the overwintering hard shiny black egg masses that encircle twigs, remove the webs in crotches, mash the young caterpillars within the webs or spray Tempo, Decathlon, Talstar, Sevin, Bt, Scimitar, Dursban, Orthene, Malathion, Diazinon, Conserve SC, insecticidal soap, SpinTor or Mimic on young trees with limited foliage. Orthene label indicates possible foliar injury to Crabapple. Foliage will grow back on healthy trees.