“The droplets appear to have lower surface tension. The stickiness of the water droplets may be due to the urea itself or to its effect on the surface tension of the water, says David Merritt at the University of Queensland, Australia, who was also involved in the study.

The next step will be to confirm that urea from urine can travel from the gut up to the mouth and be secreted onto the threads, von Byern says.

Urea is a common waste product in insect urine, and is also used in several industrial glues. Glow-worm urine is the most likely source of this urea, von Byern says. The glue was made of urea and a yet-to-be-identified peptide. The droplets were found to be composed of 99 per cent water and 1 per cent glue. To address this, Janek von Byern at the University of Vienna, Austria, and his colleagues analysed droplet samples from two glow-worm caves in Waitomo on the north island of New Zealand. Urine dropletsĪlthough this process has been studied with the naked eye, the composition and mechanism of the sticky droplet traps were unknown.

Once the insect is stuck, the larva uses its mouth to haul up the fishing line and swallow the prey. These droplets trap flying insects attracted to the blue-green light emitted by the tail of the larva. It then shuttles back and forth along the tube, spewing dozens of long silk threads from its mouth that it leaves dangling from the tube.Įach thread is up to half a metre long and beaded with sticky, mucous-like droplets. In the larval form, the glow-worm builds a mucous tube up to 40 centimetres long along the cave ceiling. Arachnocampa luminosa lives in wet caves, spending about nine months as a larva, before growing wings and turning into a fungus gnat that survives for just a few days, during which time it mates.

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