The Inelegant Moth

Script by Francie Von Mertens.

Moths circling porch lights and streetlights are a familiar sight on a summer night. Most moth species are nocturnal. Nighttime is when they should be searching for a mate or for food, not orbiting streetlights. The frantic nature of moths beating against a bright light suggests that a moth does not benefit from the relationship.

What explains this bright light attraction? Various theories have been proposed, but the one found in most textbooks has to do with a moth's navigational system. For thousands of years certain nocturnal insects have been navigating by the moon. To get from Point A to Point B in a straight line, they maintain a constant visual angle to the moon. The invention of electricity brought streetlights and house lights that interrupt and disorient this system.

A moth that orients by the moon can be thrown way off course when it encounters another light that resembles the moon. To maintain a constant angle to the new, brighter light, the moth has to circle it, and becomes more disoriented and overwhelmed in the process.

Most moths also have a general affinity for light, unlike the cockroach that scurries to the nearest nook or cranny when the lights go on. Moth enthusiasts lure moths in with specially designed illuminated traps. There's about two-thousand moth species in the University of New Hampshie insect collection, including some quite spectacular in color and size.

New Hampshire is home to an estimated five-hundred additional species yet to be found and catalogued.
Most moths have camouflage coloring, all the better to hide from predators during the day. And from collectors from UNH.