Our insect of the week for September 14, 2026 is another species dependent upon the poison ivy plant. This is another species of moth, Marathyssa basalis [LEPIDOPTERA: Euteliidae]. This species was described by Francis Walker (an English entomologist) in 1865. Fun fact – he was born on July 31, 1809 (the same year Lincoln and Darwin were born – on February 12). He wrote over 300 scientific papers.

Adults of this species are active from March through August. It occurs throughout much of eastern and central North America (including central Illinois). Fun fact – the family Euteliidae represents the second smallest family of Noctuoidea. Genetic sequencing has shown that this family is the immediate sister group to Noctuidae. It appears they diverged about 53 million years ago (Early Eocene – about the time global temperatures surged and angiosperm forests expanded).

Larvae originally fed on some members of Malpighiales (one of the largest and most diverse orders of flowering plants). This “pre-adapted” them to later feed on the toxic oils (like the urushiol found in poison ivy). To avoid daytime predators, adults mimic torn bark, dried leaves, and broken twigs. Furthermore, their musculature allows them to tightly roll their wings and some appear to do a “headstand” with their abdomen.

The specimen in this photo was collected and photographed by Frank Hitchell.