by Nanette Londeree, Master Rosarian

A caterpillar is a generic name given to the immature stage or larvae of moths and butterflies. Other common names for caterpillars are budworms, grubs, worms, leafrollers, inchworms and bagworms. There are many types of caterpillars that feed on roses, though most are considered incidental pests to roses. You won’t think so when you see whole portions of one of your roses seemingly disappear overnight!

Although most feed on leaves voraciously, only a few damage or defoliate plants extensively. Leafrollers are small, pale-green black-headed caterpillars that produce leaf mines when small and later feed inside leaves they have rolled up and tied with silk.

Tent caterpillars can be a serious nuisance. In the spring you can see the unsightly “tent” of this caterpillar covered with wriggling creatures, and the adjacent areas stripped of foliage. The picture above is out of my garden this spring – where the caterpillars appear almost overnight. These garden bad guys are not choosy – they like many other plants – apples, cherry and other fruit trees, ash, birch, willow and oak trees and more. Early in their development, they tend to eat all of the leaves on one stem or cane before moving on to the next. Later they split into smaller groups and attack several stems or canes. Twenty percent of a small tree can be defoliated by a single tent!

The eggs of the recognizable black and orange western tent caterpillar (Malacoscoma californicum pluviale) hatch in early spring just as new buds break. The young larvae begin feeding in groups; the larvae molt four times during their five – six week growing period. They do most of their damage between this time and mid-June when they begin spinning their cocoons. They attach their cocoons on a protected place on a plant, and adult moths emerge in approximately 7 – 10 days. The moths are stout-bodied and light brown and are often seen around street or porch lights on summer evenings. After mating, the female moth lays 100 – 350 eggs in a froth-covered band around small stems, or twigs on host trees. The eggs mature in three weeks but do not hatch until the following spring.

These bugs are just a nuisance – they don’t transmit diseases to humans, don’t bite and are not poisonous. Some birds will feed on them. The tachinid fly is a natural enemy that parasitizes the larvae. The most effective control for these garden bad guys is a mechanical one – remove the entire stem that contains the tent and caterpillars and destroy it (don’t add it to the compost pile!).

You can also spray plants with the biological insecticide Bacillus thuringiensis (B.t.). This control is selective; it kills only caterpillars and is relatively safe for other insects, fish, birds and warm-blooded animals.

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