Armyworms are the caterpillar (larval) form of several species of moths, known for their destructive feeding habits on crops and grasses. They are called "armyworms" because they can move in large groups, or "armies," consuming vegetation as they go. Key characteristics of armyworms:

• They have long stripes running the length of their bodies and a distinctive upside-down "Y" marking on their heads.
• They measure about 1.5 to 2 inches long at full growth.
• They hatch from clusters of eggs laid on leaves or plants near grassy areas.
• There are several common types, including fall armyworms, yellowstriped armyworms, beet armyworms, and true armyworms.
• The larvae go through several growth stages, called instars, and feed heavily on plants during this time.
• After feeding, they pupate in the soil and later emerge as moths.

Armyworms are pests primarily of grass pastures, cereal crops (such as rice, barley, oats, and corn), and turfgrass. They cause damage by eating the leaves and sometimes even the stems or seeds of plants. In times of extreme food shortage and crowding, they can "march" in large groups to find new food sources, which is how they got their name. They are most commonly found in the warm regions of the United States, especially in the southern and southeastern states, but are also present in other parts of the world like Australia. The fall armyworm, in particular, is a significant agricultural pest worldwide and can cause large economic damage to crops. Overall, armyworms are important agricultural pests due to their voracious appetite and ability to damage a wide variety of crops and grasses quickly and extensively. This summary covers their appearance, life cycle, behavior, and impact on agriculture. If you need detailed information on specific types of armyworms or control methods, I can provide that as well.