Armyworms are common agricultural pests, recognized for their destructive feeding habits. These insects, in their larval caterpillar stage, cause significant damage to a wide variety of crops and turfgrass. The term “armyworm” describes their large-scale, invasive feeding behavior as they consume vegetation.
The Armyworm Life Cycle
Armyworms undergo complete metamorphosis, a biological process involving four distinct stages: egg, larva, pupa, and adult. The life cycle begins when adult female moths lay their eggs, typically in masses containing 50 to 200 eggs, though a single female can lay up to 1,800 eggs in her lifetime. These small, dome-shaped eggs, often covered with fuzzy, grayish scales from the female’s abdomen, are usually deposited on the underside of leaves and hatch within 2 to 5 days, depending on environmental temperatures.
Upon hatching, the larval stage, known as the armyworm or caterpillar, emerges. These caterpillars are voracious feeders and can grow significantly, reaching lengths of 1.5 to 2 inches as they progress through six to seven growth stages called instars. This larval period, which typically lasts between 10 and 30 days depending on temperature, is the most damaging stage for crops, as the caterpillars consume leaves, stems, and reproductive parts of plants. Once the larva is fully grown, it burrows 2 to 8 centimeters into the soil to enter the pupal stage, often forming a silk and soil cocoon. This non-feeding, transformative stage can last from 7 to 37 days, with warmer conditions shortening the duration.
The Adult Form: A Nocturnal Moth
The pupal stage culminates in the emergence of the adult armyworm, which is a moth. These moths are moderately sized, typically possessing a wingspan of about 1.5 inches (32 to 40 millimeters). While their coloration can vary by species, many, like the fall armyworm, have gray or brown forewings and white hindwings, with males sometimes exhibiting distinct white spots on their forewings.
Adult armyworm moths are primarily nocturnal, being most active during warm, humid nights and often attracted to lights. Their main role in this stage is reproduction, as they generally do not feed on crops but instead sip nectar from flowers. The adult lifespan is relatively short, typically ranging from 7 to 21 days, with an average of about 10 days, during which females lay the majority of their eggs. These moths are also strong fliers, capable of migrating hundreds of miles, which contributes to their widespread distribution.
Varieties of Armyworms, Shared Destiny
The term “armyworm” encompasses several different species, each with unique characteristics, yet all sharing a similar life cycle and ultimate transformation. Common species include the fall armyworm (Spodoptera frugiperda), the true armyworm (Mythimna unipuncta), the beet armyworm (Spodoptera exigua), and the yellowstriped armyworm (Spodoptera ornithogalli). While their appearances may differ slightly, such as the fall armyworm often having a distinctive inverted ‘Y’ marking on its head, they all undergo complete metamorphosis.
Despite variations in their preferred host plants or geographic distribution, the fundamental life journey from egg to larva (the destructive armyworm) to pupa and finally to an adult moth remains consistent across these species. The larval stage is responsible for crop damage, while the adult moth stage is crucial for reproduction and dispersal, perpetuating the cycle.