Sticky glowworm traps are spiked with urine
Researchers found crystals of urea in the water-absorbent glue – perhaps to stop the insects drying out. Amy Middleton reports.
Sticky beads secreted by glowworms in New Zealand on their curtain-like hunting nets may contain urine, a new study shows.
The work, published in PLOS One, suggests at least part of the moist, water-absorbent droplets is made in the tiny animal’s gut and oozed through their mouth – quite different to spiders, which produce silk in a dedicated abdominal gland.
The constellation-like dots of light produced by glowworms are massive tourist magnets – particularly those of New Zealand glowworm Arachnocampa luminosa, or Titiwai.
But their delicate beauty hides malevolent intentions. Titiwai’s secretions – like all nine Arachnocampa species endemic to Australia and NZ – are used to create a sticky net which traps prey lured by glowworm’s light.
To see what was actually in these drops, Janek von Byern at the University of Vienna in Austria, Victoria Dorrer from the Technical University Wien – also in Vienna – and colleagues collected glowworms from two caves on New Zealand’s North Island and studied their secretions with electron microscopy and X-ray spectroscopy.
Along with the elements sodium, sulfur and potassium, the researchers found evidence of uric acid in the glowworm’s secretion.
So even though glowworm threads are spun from labial glands in the animal’s mouthparts, this chemical analysis suggests a portion of the droplets may originate in the gut – maybe even urine.
The researchers point out that although urea is commonly used to make resin in the bonding industry, little is known about the use of uric acid as an adhesive in nature.
The stark differences between glowworm nets and spiderwebs may point to habitat – while orb spiders build webs in exposed, dry sites, glowworms live in high-humidity environments, such as caves and forests.
Perhaps the absorbent droplets found in glowworms’ fishing lines extract atmospheric water to stop the glowworms drying out.