Nature Notebook – Dobsonfly

The earsplitting screams indicated that something other than the geocache had been found. Granted, the sight of a two-inch long female dobsonfly can provoke the same reaction from most folks. Had our visitor been a male, the screams would have been exponentially louder.

Male dobsonflies sport spectacularly large mandibles (nearly as long as their body). They may provide some degree of attractiveness to females (like deer and antlers) and they seem to be used as part of the mating ritual. Otherwise, the enormous structures are useless. The size makes it impossible for a male to actually bite anything. The female, however, has smaller but much stronger jaws and can deliver a bite capable of drawing blood.

Our female dobsonfly may have just laid eggs in a tree overhanging the nearby stream. If so, she would soon be dead. She might have recently emerged from her pupal cell dug into the ground by that stream. If so, she was waiting until nightfall to find a mate.

She wouldn’t be able to wait long…dobsonflies only live for a week as adults. The majority of a dobsonfly life cycle, up to three years, is spent as an aquatic larva called a hellgrammite.