Armyworm Damage and Identification

Armyworms are a serious crop pest in tropical and subtropical regions. These hungry caterpillars can defoliate entire fields of crops before moving on in their search for more food, with devastating economic consequences.

What are armyworms?

Despite their name, armyworms are not worms at all; they’re actually caterpillars of moths from the family Noctuidae. Like many other types of caterpillars, armyworms can cause significant damage to plants. They mostly feed on leaves and turfgrass, but may also attack the stems of plants.

Armyworms are voracious eaters and, when present in large numbers, can consume enough foliage to destroy a whole field of crops. In rare cases, there may be so many armyworms in an area that their food supply is almost completely depleted. When this happens, the bugs will leave the area en masse in their search for more food, appearing to ‘march’ out of the crop.

How to identify armyworms

There are several species of armyworms found in the United States. Their larvae are typically 1.5 to 2 inches long, and look like caterpillars of other species. They vary in color and may be gray, green, yellow-green, greenish-brown, or black.

Armyworms also have white, cream, orange, or dark-brown stripes on their sides that run down the length of their abdomen. The head may also vary in color, but usually has a mottled appearance.

Fall armyworms (one of the most significant armyworm species in the United States) may be identified by the white, inverted, Y-shaped marking between their eyes.

How to tell armyworms apart from other types of pests

Armyworms look very similar to other types of caterpillar-like pests, so how can you tell them apart?

They key to correctly identifying armyworms is to look for the long, pale stripes on the sides of their abdomen. These are present in all armyworm species, but not in other types of larvae. Armyworms are also smooth and have no obvious hairs, which distinguishes them from caterpillar species with hairs or bristles. Armyworms also curl up tightly when disturbed, while other types of larvae may wiggle or try to escape.

Which plants are affected by armyworms?

Fall armyworms are notorious for feeding on turf grasses, but they are actually known to attack over 350 species of plants. In large numbers, they can cause major damage to maize, rice, sugarcane, barley, buckwheat, cotton, corn, sugar beet and wheat crops.

Keep in mind!

They may also feed on fruit crops such as apple, orange, grape, papaya, peach, and strawberry. Armyworms are also known to attack a number of flowering plants.

When present in large numbers, armyworms can destroy whole fields of crops by consuming the foliage of plants. When their population grows too large for the area to sustain it, they ‘march’ out of the fields in an army-like fashion as they look for new host plants.

Damage caused by armyworms

Armyworms usually feed on the leaves of plants, causing holes in leaf tissue and giving the edges of leaves a tattered appearance. When attacking grass-like plants, these bugs tend to target the leaf whorl, where leaves radiate out from the stem of the plant. Armyworms can also tunnel into fruits and eat the buds and stems of plants, and larger bugs can even cut plants off completely at the base.

Where are armyworms most common?

Armyworms are found in many parts of the world, including North America. In the United States, armyworms are common in Eastern and Central regions, and are especially abundant East of the Rocky Mountains. They can’t survive the winter in cooler, northern climates, but are known to overwinter in southern Florida and southern Texas.

Are armyworms dangerous to humans or pets?

Armyworms can cause devastating economic damage, but they do not bite, sting, or transmit diseases. Therefore, they are not directly harmful to humans or animals. They are also unlikely to do any harm when swallowed, so don’t panic if you catch your dog eating a few.

How big of a problem are armyworms?

Armyworm invasions can be catastrophic to farmers, as large numbers of the larvae can consume entire fields of crops. These pests aren’t fussy eaters and, though they prefer grasses, will gobble up over 350 different plant species.

The extent of the armyworm problem varies depending on where you live. In the northern states of America, excessive armyworm damage is a rare occurrence, as the temperatures in these regions are usually too low for the larvae to thrive.

However, armyworms do very well in warmer climates and are a major problem in Southern states, where they do extensive damage to crops such as corn, rice, sorghum, and cotton.

The armyworm is also a big problem in other tropical and subtropical parts of the world. In Brazil, the eating habits of fall armyworms cost the country’s economy $600 million per year in management efforts.

In the last few years, armyworms have made their way to Africa as an invasive species. They have since spread to several countries in Western and Central regions of the continent and are wreaking havoc on crops.


Armyworms are caterpillars of several species of moths, and are a serious problem for farmers in tropical and subtropical regions. These major crop pests are known to feed on over 350 plant species from grasses to vegetables, fruits, cereals, and cotton. A large armyworm population can demolish the foliage of whole fields of crop plants, before ‘marching’ out en masse to look for new sources of food.

Although armyworms are present in several Central and Eastern States, they cannot overwinter in cooler, northern climates. They are more of a problem in southern Florida and southern Texas, where they thrive in the warm weather and can multiply rapidly.

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