Through the eyes of a child, cataloging the many shapes, sizes, and colors of caterpillars is a fascinating exercise in basic entomology, but for an adult, the sudden appearance of caterpillars in the landscape can be a bittersweet discovery. Having caterpillars may indicate that your landscape has become a breeding ground for butterflies, but it may also spell doom for any host plants nearby, since caterpillars are voracious eaters.
There are many solutions for caterpillars in the landscape, ranging from patient observation to applications of targeted insecticides, depending on the stress level these Lepidoptera larvae cause to you and your plants. Before you break out the big guns, though, it may behoove you to observe the caterpillars at work to assess the true extent of the problem.
Types of Caterpillar Trouble
Before you deal with an unknown caterpillar, it’s a good idea to try to identify it in order to avoid some of the brutal stings many species are capable of dealing. Stinging caterpillars typically bear their barbs openly, emerging from their backs like stiff, brightly colored weapons, but a few may have barbs that look more like long, wiry hairs. Never handle a suspected stinging caterpillar with your bare hands – these larvae carry real poison and can inflict real damage on humans. Fortunately, the stinging caterpillars are uncommon in home landscaping.
The tent caterpillars are a special group that creates huge silken webs in trees, often encompassing many leaves and small branches as they mature. These pests can seriously injure trees and bushes with their feeding, which usually occurs inside the tent. A single, small tent of caterpillars in the landscape is unsightly, but can be easily tolerated by a mature plant – many in a single tree early in the season can cause devastating defoliation. If tent caterpillars appear in the fall on deciduous trees, they can often be ignored, since your tree is already preparing to shed the foliage where the caterpillars are feeding.
Other notorious caterpillars, such as hornworms, are voracious eaters and capable of destroying entire plants in a few days. These caterpillars may appear suddenly in groups, chewing their way out from the center of an infested plant and spreading further apart as they mature. Although caterpillars are usually picky eaters, choosing just a few hosts to feed upon, those few chosen plants may be in serious jeopardy if caterpillars are numerous.
Dealing with Caterpillar Infestations
Many birds and insects think caterpillars are tasty and will flock to gardens where broad-spectrum pesticide use has been discontinued to help with your caterpillar problems. If the caterpillars don’t seem to be thinning within a few days of their appearance, you may have to intervene. Sometimes, the caterpillars in your landscape are simply too numerous for their natural enemies to contain, or those enemies may have not yet realized that a cache of caterpillars is active nearby.
In either case, you can help out by hand-picking caterpillars from plants. It is sometimes tedious work, but removing caterpillars from affected plants (remember to wear gloves) and dunking them in a bucket of soapy water can be strangely therapeutic when these pests are threatening your favorite plants.
When hand-picking, it’s important to check for caterpillars at the same time each day, looking deep into the canopy of affected plants, until you have a difficult time locating even one caterpillar. Continue to monitor for caterpillars weekly, in case a new brood has hatched.
If hand-picking caterpillars is impractical, or you are a little more squeamish than you’d like to admit, a biological spray called Bacillus thuringiensis (Bt) is available for use by homeowners. This product is derived from a soil-borne bacteria of the same name that releases a specific protein when it enters a caterpillar’s gut, increasing the gut’s permeability. It kills caterpillars over a few days, so don’t be shocked if they aren’t immediately falling from your plants after you’ve sprayed.
Bt is effective on all kinds of caterpillars, but has a short life and may need to be reapplied every week until the caterpillars are all gone. It can be harder to treat tent caterpillars with this product, but if you tear each bag open and spray the caterpillars directly, you will increase Bt’s effectiveness.
Very tall trees or widespread problems with caterpillars may require a pest control expert. Caterpillars in trees are difficult to treat without special equipment that can reach accurately into the canopy. Pest control specialists use a variety of chemicals against caterpillars, make sure that you specify that you want to preserve beneficial insects if you need to call in the cavalry.
Terry Jenkins is a freelance writer on a wide range of topics including gardening, pest control, and occasionally home improvement.