True caterpillars, as opposed to sawfly larvae, are all members of the Lepodoptera Family of insects. They all eventually develop into butterflies or months. They are sometimes confused with sawfly larvae which are unrelated critters.

Even though they are all caterpillars, there are still several types found in the home landscape:

1. Leaf Feeding Caterpillars - Several species of caterpillars feed on the leaves of ornamental trees and shrubs. In most cases, the adults lay their eggs on the bark or other parts of the tree in autumn or early spring. The larvae hatch in the warmth of the sun and begin to feed. Later, they pupate and turn into the adult moth or butterfly which flies around and lays egg masses for the following year's generation.

These types of caterpillars would include the larval form of gypsy moth, cankerworms and forest tent caterpillars. All of them, including the confusingly named forest tent caterpillar, do not form webbed nests or tents.

2. Tent Caterpillars and Fall Webworms - As the name implies, these caterpillars form a silky tent or web in the tree or shrub during their larval stage. Generally, these units are for shelter from predators and the caterpillars may actually eat only within the expanding web. After they have reached a certain size, the caterpillars drop to the ground and pupate in the soil before the adult emerges to lay eggs again.

The Eastern tent caterpillar appears in the spring and makes its tent over the point where two branches merge (the crotch). They feed into early summer primarily on crabapples and then are gone for the season. Generally, the do very minimal damage to the tree and are mostly an aesthetic problem.

Fall webworms appear in the late summer and form their tents or webs at the tips of branches of may species of trees. Again, they do minimal damage and are mostly an aesthetic problem.

3. Bagworms - These caterpillars form an individual bag for itself. As they grow, so does the bag until it eventually stops feeding and pupates. The female bagworm spends her entire life inside her bag where she lays hundreds of eggs. The eggs spend the winter in the bag and hatch the following spring. Again, these are generally more of an aesthetic problem.

These insects feed on the tissue of leaves and may eat the entire leaf or leave just the veins of the leaf behind. In severe cases such as with Gypsy moth caterpillars, the entire tree may be defoliated while others such as Eastern tent caterpillars generally do little damage to the overall canopy.

Although even total defoliation of deciduous trees (not evergreens) will not kill the plant, repeated serious infestations over several seasons can weaken the tree. Such trees are more susceptible to other environmental stresses. Over a period of years, this could lead to the death or weakening of the tree.

 
 

Since these are all true caterpillars (not sawfly larvae), they are susceptible to the biological control product called Bacillus thuringiensis (Bt). This is a nice product since it only kills members of the Lepodoptera Family. You do need to be sure that there are no endangered species of moths or caterpillars in your area before using Bt. It does not discriminate between "good" caterpillars and "bad" caterpillars.

For small infestations or small plants, you can sometimes hand pick the caterpillars. Snip off webworm nests on small, ornamental trees, if you can easily reach them. Pull apart the nests of the Eastern tent caterpillars but do NOT burn them off with a blow torch.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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