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Publication #SP117

Armyworms1

F.A. Johnson and J.L. Castner2

The moths known as armyworms belong to the family Noctuidae of the order Lepidoptera. The family name refers to the nocturnal nature of the adults. While the adult stage causes no direct damage, the immature worm stage feeds, often voraciously, on plants.

Hosts include many vegetables, agronomic crops and grasses. The worms prefer to feed on foliage but may attack the stems, fruit or even tubers of certain host plants. Damage can be extensive. Armyworms are active from spring until fall. The different armyworms are similar in color, size and markings and can be difficult to tell apart.

Most armyworms go through five larval stages within 14 to 21 days (species and temperature dependent). As they grow, their ability to consume plant tissue increases and they can chew large holes in leaves or strip an entire plant. After maturity the worms move to the soil, dig to about 1" deep, and pupate. After seven to 14 days, they emerge as adults. The entire life cycle ranges from 24 to 36 days, with an average of 28 to 30. In Florida there can be many generations per year, usually peaking June through September. Adults migrate north as the weather warms, large numbers often flying long distances before descending to lay their eggs.

  • Fall armyworm egg mass (Plate 1). The female lays eggs in masses usually on the undersides of host plant leaves. The round or oblong mass contains 50 to 150 eggs, depending on the individual female and the species. The female moth covers the egg mass with hair from her body, giving it a felt-like appearance. The mass is usually tan, buff or off-white and is 1/4" to 3/8" in diameter or length.

  • Fall armyworm eggs hatching (Plate 2). Eggs hatch two to five days after they are laid, with hatching time quicker as the weather warms. The eggs turn black just before they hatch. Young caterpillars tend to be black. They congregate in the vicinity of hatching for about 24 to 48 hours, after which they migrate to different plants and/or feeding sites. Young worms scarify the leaves as they feed, leaving a thin, windowpane appearance.

  • Fall armyworm, Spodoptera frugiperda, (Plate 3 and Plate 4), is probably the most damaging Florida armyworm (Plate 5 and Plate 6). It may be light tan to shades of gray or green. The head capsule is usually shiny black or brown, with a prominent yellow or white inverted Y marking on the front. The body has many black tubercles, or round, mole-like structures. When fully grown, the caterpillar reaches 1-1/2".

  • Beet armyworm, Spodoptera exigua (Plate 7), is about 1-1/4" long when mature. The body is usually some shade of green but can vary, with prominent dark lateral bands running its full length. There is a single prominent black spot behind the head, about halfway up the side of the body and right above the second pair of true legs.

  • Southern armyworm, Spodoptera eridania (Plate 8) is one of the more robust armyworms and is often called a "climbing cutworm." The mature larva can exceed 1-1/2" in length and can be either gray or pinkish. It strongly resembles the yellowstriped armyworm. The head of the southern armyworm is usually yellow to light-orange. The lateral stripe on the side of the body is interrupted by a large dark patch at the beginning of the abdomen.

  • Yellowstriped armyworm, Spodoptera ornithogalli (Plate 9), has a brownish head with a pale-yellow inverted V on the upper front. It has distinct bright-yellow lines on the top of the sides of the body. The yellowstriped armyworm occurs with both overall pale- and dark-colored bodies. It has two rows of black triangle-shaped markings running the length of the body. Each row is offset from the center of the back. A thin white line runs lengthwise through each series of dark triangles.

  • True armyworm, Pseudaletia unipuncta (Plate 10), is brownish and is frequently mistaken for the fall armyworm because the size and many of the body marking are similar. The outstanding difference is that starting from the center of the back, the true armyworm has a dark lengthwise band and a pale lengthwise band just below it, and the fall armyworm has the reverse coloration of bands.

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Footnotes

1.

This document is SP117, one of a series of the Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date November 1992. Reviewed May 2003. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.

2.

F.A. Johnson, Professor; J.L. Castner, Scientific Photographer; Department of Entomology and Nematology, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611. The term plates, where used in this document, refers to color photographs that can be displayed on screen from the FAIRS CD-ROM. These photographs are not included in the printed document.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.