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June 23, 2021
As you pull up to the Susquehanna River, on a mid-June evening, from a distance, it would appear that the excitement of the Hexagenia mayfly hatch is in the sheer number of bugs in the air. The swarms are so impressive that you can hear their collective wings crashing into one another as they take flight. As extraordinary as the swarms may be, each one of these beauties is going through an equally exciting transformation.
Hexagenia bilineata nymphs emerge from their underwater burrows and swim to the surface before swarming along the Susquehanna River in almost unbelievable numbers. The bugs spend a day or two in their new immature subimago stage before molting one more time into their final form. In this mature imago stage, they breed, and the female lays her eggs on the water, starting the cycle all over again.
Like all mayflies, Hexagenia bilineata spend most of their life underwater and rely on clean water and a healthy aquatic ecosystem to survive. The increased abundance of mayfly hatches on the Susquehanna over the last few years indicates that water quality is on the mend. With any luck and a whole bunch of upstream work by organizations like the Alliance, future years mayfly hatches on the Susquehanna will yield even more significant numbers!
From the large scale of the swarms down to the details, the hex hatch is a show worth experiencing. The hatch occurs every year in mid to late June. If you live near the lower Susquehanna River, go out of your way to check it out!