What are all those dragonflies doing at the beach?!
July 29, 2024
Beachgoers in Rhode Island this past Sunday were expecting sand, waves, and sunshine. Taking cover from a giant swarm of dragonflies likely wasn't on their agenda for the day. Some people ran, some looked to the skies in awe, and others got out their phone to record. While it certainly is a unique sight, for dragonflies, it was just another part of their life cycle. We have several migratory dragonfly species in the United States, one of the most common in the northeast being the common green darner (Anax junius). After reaching the upper midwest around May, the new generation migrates south between late July and mid October until they reach the Gulf of Mexico or southeastern states.
It's actually not all that unusal that this swarm flew over a beach, as dragonflies appear to prefer to migrate along coastlines or lakeshores, during the day when it's not too windy. It appears that not only was it prime beachgoing conditions on Sunday, but also prime dragonfly flight conditions! One study indicated that the common green darner can fly up to 75 miles in one day, and travels up to 48 miles per hour (groundspeed equivalent).1 Although they pause their migrations for a couple days at a time to feed, the journey is complete within a couple months.
Dragonflies are carnivorous insects, meaning they consume other insects for food. One of their favorite snacks? Mosquitoes. While dragonflies may not be our most welcome beach guests, they certainly save us from more than a few bug bites each year! They are valuable members of the ecological community.
Written by Nicole Bell.
1: Radio-tracking reveals how wind and temperature influence the pace of daytime insect migration | Biology Letters (royalsocietypublishing.org)