Our insect of the week for July 6, 2026 is Hexagenia bilineata [Ephemeroptera: Ephemeridae]. This species was described by the American entomologist, Thomas Say in 1824 (as Baetis bilineata). I chose this insect to celebrate the recent (June 18 – 22, 2026) emergence of adults along the Illinois River near Peoria.

Nymphs are aquatic and live in mud in slow moving streams and still waters. They feed on plant material and other organic debris. Adults do not eat and live a very short time.

When ready to emerge as an adult, the nymph swims to the water’s surface at night and the subimago emerges. The wings are cloudy. In less than a day, these subimagos moult into adults (imagos) which then reproduce. Mayflies are one fo the few insects which moult as adults. Females are often much larger than males.

Mayflies are an ancient group of insects (their fossil history goes back over 300 million years). Since adults have short lives, most fossils are of nymphs.

I hope you enjoy these photos I took of individuals (females) near then end of the recent emergence in East Peoria, Illinois (Tazewell County) on June 22, 2026. Most of these images are stacked photos. I wanted to showcase the large compound eyes and short antenna on these individuals with the close macro photos.