You Are Here: Management Updates 2001 Archive July 23, 2001

Date: July 23, 2001
Category: Insects
Subject: All About Caterpillars

Now that the ARMYWORM INVASION seems to be slowing down a bit in most areas, people are seeing various caterpillars in their lawns or fairways or athletic fields, and wondering whether they are webworms (which occur commonly on lawns throughout the Northeast but seldom cause severe damage) or cutworms (which are often pests on golf courses) or a second generation of armyworms.

All three types of caterpillars can be found in turf throughout the summer. They are smooth-bodied, not sporting the irritating hairs that are common on gypsy moths.

In many areas, ARMYWORMS are currently in the moth stage, and may be flying in very large numbers. The MOTHS are typical night flying moths, with a fairly uniform light tan or reddish brown color. Sometimes you can see a distinct, albeit small, white spot near the middle of the forewing. They have a wing span of about two inches.

ARMYWORM CATERPILLARS are dark colored (variously described as a dark green or black or brown) on the top, with light colored stripes along the side. Sometimes these marginal stripes have a hint of pink. They also have a light-colored "broken" line that runs along the middle of the back. The head capsule usually has two shades of brown, intermeshed in a "honeycomb" effect. Caterpillars are nearly two inches long when they complete their development, and the bodies are about the diameter of a pencil. Smaller caterpillars may be lighter green in color, and the very young caterpillars sometimes "loop" along like inchworms. Like cutworms and webworms, armyworms are NOT hairy.

The forewings of BLACK CUTWORM MOTHS are dark gray mottled with black markings. There often is a black dagger-shaped mark near the hind margin of the front wing. Like many moths, black cutworms are attracted to lights at night. They have a wing span of about two inches.

CUTWORM CATERPILLARS (seldom seen on home lawns) are a bit fatter than armyworms (slightly bigger around than a pencil), and tend to curl up into a tight "ball" when disturbed. The BLACK CUTWORM, the most common species found on golf courses in New England, is normally a dark gray or olive green on the top half of the body, and a lighter gray on the underside. It has a faint, indistinct line along each side of the body. The spiracles (the holes on the body through which insects breathe) are black. If one looks at a black cutworm with some magnification (e.g., a 15X hand lens), the surface of the body resembles a cobblestone pavement.

SOD WEBWORMS, sometimes called "snout moths", can be pests of home lawns in New England. When at rest, they project certain structures of their mouthparts forward, so it looks like they have a "snout". They also fold their wings tightly around their bodies when at rest, so they look almost tubular. When resting on a blade of grass, they are very difficult to see. But when disturbed (as, for example, when one is mowing a lawn in the evening), sod webworms will flit along, barely above the turf surface. A quick glance suggests the moths are a very light tan or white, but closer inspection reveals bands of silver, brown, gold, or black running longitudinally along the wing. The wingspan is usually about one inch.

WEBWORM CATERPILLARS may be any of a wide range of colors, from green to beige, brown, or gray. Colors may vary even within a species. Most webworm species have dark circular spots scattered throughout the body. Body length varies with species, but generally the full-grown caterpillars will be about one inch long. Head capsules often are dark in the young caterpillars, and usually are light brown in mature caterpillars.

So if a turf caterpillar has STRIPES, it probably is either one of the cutworm or armyworm species. If it has SPOTS, it is more likely to be one of the webworm species.

LOOKING FOR CATERPILLARS IN ALL THE RIGHT PLACES

All of these caterpillars (i.e., armyworms, cutworms, and webworms) spend much of their time in the thatch. While there, they create burrows which are often lined with green "frass" (entomologists' word for caterpillar excrement). If you inspect the thatch with your fingertips, and find burrows or green frass, you can be pretty certain that one caterpillar or another is active in the area.

Another way to monitor for caterpillar activity is to use a soapy mix to irritate caterpillars to the surface. Put one or two tablespoons of a lemon-scented liquid dish detergent in one or two gallons of water, and stir it up so it is frothy. Pour the mix over an area that is one or two feet on each side. Within a minute or two, medium and large caterpillars will wriggle to the surface, trying to avoid the irritation of the soapy fluid on their skins. (Other creatures, including earthworms and adult beetles, will also wriggle to the surface.)

NOTE - The soapy water acts like a magnifying glass on a hot, sunny day, so you can burn the turf if you are not careful. Be sure to rinse the "treated" area after you have finished counting insects, to dilute the soap and remove it from the surface.

- Submitted by: Dr. Pat Vittum