Does every stage of a glow-worm glow?

Find out why these bioluminescent bugs light up the night

Glow-worms glowing
Despite their name, these bioluminescent bugs are beetles, not worms. © iStock


Yes. It is in fact a bit of an oddity that, as well as the wingless female, the larva and the winged male of the glow-worm also glow. However, only the female glows brightly, and these are the ‘grass stars’ sometimes spotted in short turf on warm summer evenings.

It is generally accepted that the female glows to allow a male to find her for mating (female moths similarly release pheromone scents to attract partners in the dark). Why the male glows is still not known for certain – it could be an evolutionary hangover. 

There is also a theory that glowing evolved to serve as a warning to predators that these insects contain noxious chemicals and will therefore taste foul. This is analogous to the bright warning colours of wasps, in which case it would be advantageous for males and larvae to glow too.


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