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This blog post will teach you everything you need to know about army worms, including what they look like and how to get rid of them.
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Introduction
Assuming you are referring to the common armyworm (Spodoptera exigua), here is some information on what this caterpillar looks like.
The common armyworm is a destructive caterpillar that feeds on a wide range of crops, including cereals, cotton, and vegetables. The adult moth is brown or gray, with a wingspan of about 1 inch. The caterpillars are green or brown, with dark stripes running lengthwise along their bodies. Fully grown caterpillars can reach up to 2 inches in length.
What does an army worm look like?
The adult army worm is a nocturnal moth. The body is dark gray to almost black and the wingspan is about 32 mm. The front wings have a characteristic yellow-orange “Y” or “V” mark. The hind wings are paler. There are small tufts of black hair on the leading edge of each front wing. Armyworms get their name from their habit of migrating in large numbers and stripping fields and gardens of vegetation.
Army worm larvae
The common name of armyworm is applied to the larval stage of numerous moths in several families. Armyworms are usually numbered among the most destructive of agricultural pests. This voracious feeding habit is frequently witnessed in nature, where outbreaks sometimes occur. Many farmers have experienced complete crop losses due to migrating armyworms.
Larvae vary considerably in appearance, but most are bright green, with a brown or black head. Some have stripes running along the length of their bodies, while others may be solid-colored. The size of larvae also varies, depending on the species, but most are about 1 inch (2.5 cm) long when fully grown.
Armyworm larvae typically hatch from eggs laid by adult moths in late spring or early summer. The young caterpillars begin feeding immediately and continue for several weeks before pupating. Adults emerge from pupae a few weeks later and mate soon afterward. Females lay eggs on various types of vegetation, and the cycle begins anew.
Army worm pupae
An armyworm is the caterpillar stage of several different types of moths. Armyworms are destructive pests that can strip a plant of its leaves in a very short time. The adult moths are brown or gray and have wingspans of 1 to 1-1/2 inches. They are strong fliers and are attracted to lights at night. The eggs are laid in masses on the undersides of leaves and hatch in 3 to 4 days.
The newly hatched larvae are small and black with a light-colored stripe running down their backs. As they feed, they grow rapidly and molt (shed their skins) 4 or 5 times. When fully grown, armyworms are 1 to 1-1/2 inches long. Just before pupation, they burrow into the soil to pupate. Adults emerge from the pupae in about 10 days if conditions are favorable (moist soil and warm temperatures). There may be 2 or 3 generations per year.
Army worm life cycle
Army worms are the caterpillar stage of the Noctuidae family of moths. They get their name because they travel in large groups and can strip a field of vegetation in a short amount of time. Army worms are found in most continents except for Antarctica.
Army worm eggs
Army worm eggs are small, round andreddish-brown in color. They are oftenlaid in clusters on the leaves of plants.Once hatched, the larvae (caterpillars)begin to feed on the leaves of the plant.They are small and green in color witha dark stripe running down their back.As they mature, they grow to about 2inches in length and turn brown orblack. The mature caterpillars then spin cocoons and pupate inside of them. After a few weeks, they emerge as adult moths.
Army worm larvae
Larvae (caterpillars) hatch from eggs in 4 to 10 days, depending on temperature. The body color of armyworm caterpillars can vary from light green to almost black and commonly have a stripe down the middle of the back and two stripes along each side. Armyworms have a dark head capsule with a light inverted “Y” on it. Full grown caterpillars are about 1 inch long.
Army worm pupae
Army worms go through 4 stages in their life cycle – egg, larva, pupa and adult. The entire process takes about 3-4 weeks.
Eggs are deposited in masses on the underside of leaves. They are oval shaped and range in color from pale green to yellow.
Larvae hatch from eggs and begin feeding immediately. They go through several stages of growth, molting their skin as they get larger. At full size, they are about 1 inch long and can be various shades of green or brown with a dark stripe running down their backs. Some may also have stripes on their sides.
Pupae are brown and taper to a point at both ends. They do not feed during this stage, but remain stationary until they emerge as adults.
Adults are dark-colored moths with a wingspan of about 1 inch. They have brown or gray stripes running along the length of their bodies. Females lay eggs soon after emerging from the pupal stage, starting the cycle over again.”
Army worm damage
Army worms are the caterpillars of several Noctuid moth species. The true army worm, Pseudaletia unipuncta, is a serious pest of corn, small grains, turf and grasses. Adults are grayish-brown moths with a one-half inch wingspan. They have a dark stripe running along each side and a copper stripe in the center of the wing. Females lay groups of 50 to 100 small, round eggs on the underside of leaves. In three to five days, larvae hatch and begin feeding.
Larvae go through six instars (growth stages) in about three weeks. They are shiny black with light stripes running along their sides and reach one to one and one-half inches in length at maturity. Army worms are voracious feeders and will strip leaves from plants, eating all but the larger veins. They often move in large groups (hence the name), so extensive damage can occur quickly.
Army worm control
The army worm can inflict serious damage to crops, making army worm control a high priority for farmers. This worm is small but incredibly destructive, and can quickly decimate a crop if left unchecked. Army worms are most active at night, so identifying them can be difficult. However, there are a few telltale signs that will help you identify an army worm infestation.
Physical control
Hand picking and destroying the caterpillars is the best physical control for preventing army worm damage. This is most effective when combined with other methods such as biological control, since it can be difficult to remove all of the caterpillars by hand.
Biological control
Trichogramma wasps are tiny parasitic wasps that invade the egg sacs of caterpillars, such as armyworms, and lay their own eggs inside them. The new generation of wasps then hatches and eats the host caterpillar from the inside out. This provides very effective control with very little effort, as the parasitoids will spread through the entire caterpillar population on their own. You can purchase these beneficial insects online or at some garden supply stores
Chemical control
For chemical control, armyworms are most vulnerable when they are small caterpillars. Insecticides with the active ingredients Bacillus thuringiensis (Bt) or spinosad are effective on young caterpillars. Application timing is critical for Bt products—they must be applied before the caterpillars have consumed enough of the treated leaves to cause serious damage, but after caterpillars have begun feeding. For more information on Bt products, consult the New England IPM Center’s Bt Products fact sheet.
Some armyworm species have developed resistance to synthetic insecticides, particularly those in the pyrethroid family. If you suspect that your population is resistant, contact your local Cooperative Extension office for assistance with caterpillar identification and management recommendations.
