It cannot survive overwinter in below freezing temperatures, so it only survives the winter in the most southern regions of the United States, namely Texas and Florida. The fall armyworm is widely distributed in eastern and central North America and in South America. They also develop dark spots with spines. As they develop through instars, they become browner with white lengthwise lines. The first larval instar is light colored with a larger dark head. There is slight sexual dimorphism, with males having more patterns and a distinct white spot on each of their forewings. The adult moths are 32 to 40 millimetres ( 1 + 1⁄ 4 to 1 + 1⁄ 2 in) wing tip to wing tip, with a brown or gray forewing, and a white hindwing. Outbreaks of the true armyworm usually occur during the early part of the summer the fall armyworm does most damage in the late summer in the southern part of the United States, and early fall in the northern regions. The fall armyworm is active at a different time of year from the true armyworm, another species in the order Lepidoptera and family Noctuidae, but of the genus Mythimna. Another remarkable trait of the larva is that they consistently practice cannibalism, despite its fitness costs. It is also a notable case for studying sympatric speciation, as it appears to be diverging into two species currently. Because of its propensity for destruction, the fall armyworm's habits and possibilities for crop protection have been studied in depth. Its scientific name derives from frugiperda, which is Latin for lost fruit, named because of the species' ability to destroy crops. It is regarded as a pest and can damage and destroy a wide variety of crops, which causes large economic damage. The term 'armyworm' can refer to several species, often describing the large-scale invasive behavior of the species' larval stage. The fall armyworm ( Spodoptera frugiperda) is a species in the order Lepidoptera and one of the species of the fall armyworm moths distinguished by their larval life stage.

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