Identification
Armyworms are caterpillars that vary in color from green to brown with distinctive longitudinal stripes along their bodies. They grow up to 1.5 inches long and have a smooth, cylindrical body. The adult moth has a wingspan of approximately 1.5 inches and features grayish-brown forewings with mottled patterns. These pests are widespread in North America, South America, Africa, and Asia, particularly in agricultural and grassy environments.
Lifecycle & Reproduction
Armyworms undergo complete metamorphosis. Females lay clusters of eggs on leaves, which hatch within a few days. The larvae develop through six instars over 2-3 weeks before pupating in the soil. The pupal stage lasts 10-14 days, after which adult moths emerge. Multiple generations can occur each year, especially in warm climates.
Habits, Diet & Behavior
Armyworms are nocturnal feeders that consume plant foliage, stems, and grain heads. They primarily target grasses, corn, rice, wheat, and turfgrass. Larvae feed in groups during early stages, then disperse as they mature. They are known for their rapid migration and ability to devastate entire fields within days.
Where You’ll Find Them / Typical Locations
These pests are commonly found in agricultural fields, pastures, golf courses, and home lawns. They prefer warm, humid conditions and are most active during late summer and fall. Larvae can be found hiding under plant debris during the day.
Threats & Danger
Armyworms pose a severe threat to crops, leading to defoliation, reduced yields, and economic losses. Their feeding weakens plants, making them more susceptible to secondary infections. Large outbreaks can devastate entire fields, particularly in monoculture farming systems.
Prevention
- Rotate crops to disrupt their lifecycle.
- Encourage natural predators such as birds, parasitic wasps, and ground beetles.
- Remove plant debris to eliminate breeding sites.
- Maintain proper irrigation and fertilization to strengthen plants against infestation.
- Monitor fields regularly to detect early signs of infestation.
Signs of Infestation
- Ragged, chewed leaves and missing foliage.
- Bare patches in turfgrass and pastures.
- Presence of large groups of larvae moving in a coordinated manner.
- Frass (caterpillar excrement) on leaves and soil.
- Increased sightings of adult moths in fields and around lights at night.
How to Get Rid of It
- Handpick and remove larvae in small infestations.
- Apply Bacillus thuringiensis (Bt) to target young larvae.
- Use insecticidal soaps or neem oil for organic control.
- Introduce beneficial insects such as lacewings and predatory beetles.
- Apply chemical insecticides labeled for armyworm control in severe cases.