P&PDL Picture of the Week for
October 22, 2007

Glow in the Dark Worms

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Each year many strange looking insects are submitted to our laboratory for identification, but one of the most spooky is a worm that glows in the dark.  These eerie insects are usually found in the soil emitting a soft iridescent glow.  Speculation surrounding their identity and cause for the glow is usually more bizarre than the insect itself.  Rest assured that these are not mutated, irradiated, or alien life forms but rather, are simply the immature stage of common lightning beetles (fireflies).  After the lightning beetles have disappeared, their eggs laid in the soil hatch into these interesting larvae. The ‘glow’ that they emit is created in the same way that lightning beetles create light.  That is, a chemical reaction in which the enzyme luciferase in the insect’s body reacts with luciferin in the presence of oxygen.  The result is bioluminescence or light.  The marvelous thing about this light is that it is very efficient. Nearly 100% of the energy input is turned into light as compared to only 60% in man-made fluorescent lights.

Lightning beetle larvae are predacious upon other small invertebrates in the soil.  They are most common in moist, highly organic soils.  They present no danger to people or pets, nor do they pose a threat to plants.  At this time of year they are principally a curiosity – although it is curious that they are most often reported near Halloween time.  Hmmm.


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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service