Sarah Webb, of Rangiora High School, asks :-

Why do native earth worms secrete a bioluminescent substance?

Jo Springett, a soil zoologist at AgResearch, Palmerston North, responded.

Bioluminescence, or cold light, is caused by a substance luciferin which, when broken down by the enzyme luciferase, gives off light, rather than heat as is the case with most metabolic processes. Some species of earthworms emit bioluminescence in the slime which they secrete through pores along their back or which leaks out of a damaged worm.

No one has a good explanation of why they do this. It may be that it is just a physiological accident. Being able to flash light when irritated may give them some ecological advantage. Dr Peter Johns, a scientist at Canterbury University has suggested that the 'pool' of light that a damaged earthworm makes may serve to divert the attention of a predator, such as a Kiwi, and allow the worm to escape while the bird is still pecking at the light. Underground a flash of light may startle or disorientate predators such as large beetle larvae. You may be able to think of other possible ways in which a glow or flash of light could help a worm to survive. The worms themselves do not have eyes and are only slightly sensitive to light.

The Maori use these worms as a fishing bob, eels are particularly attracted to the glow of the bob. If you dig at night a lot of damaged small worms make the ground sparkle like a starry sky.