Slugs are generally content to lazily munch garden greens, but one of these lethargic molluscs has recently been spotted taking to the air, descending vertically down a string of slime like a spider dangling from a line of silk.
The discovery represents a new type of locomotion never seen before in slugs.
John Gould, an ecologist at the University of Newcastle in Australia, was conducting fieldwork on frogs on Kooragang Island, New South Wales, when he found a striped field slug (Lehmannia nyctelia) hovering about a metre above the ground.
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鈥淎t first, I thought I had stumbled upon a spider that was making its way to the ground on a silk thread,鈥� says Gould.
The slug was suspended on a taut slime thread stretched from the top of a fence to some gravel below. Gould watched as the slug glided down about half the thread鈥檚 length in only a couple of minutes 鈥� fast, for a slug.
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鈥淲hen John first told me about it, I just didn鈥檛 believe it,鈥� says Jose Valdez, a conservation biologist at the German Centre for Integrative Biodiversity Research in Leipzig and co-author of the new study.
After seeing Gould鈥檚 video footage and delving into the scientific literature, it became clear to Valdez that this was a unique observation. Leopard slugs (Limax maximus) will mate while hanging by a rope of thick mucus, says Valdez, but this was 鈥渁 single slug with a relatively thin mucus [thread], descending towards the ground before it went on its way鈥�.
These mucus slides may be useful for quickly escaping predators like ants or lizards.
鈥淚t is possible that descending on a single mucus thread saves both mucus and energy, as it鈥檚 such a thin line of material that needs to be produced,鈥� says Gould.
A single observation like this isn鈥檛 enough to make generalised claims about the behaviour of an entire population of slugs, says Jann Vendetti at the Natural History Museum of Los Angeles County. 鈥淏ut it could inspire more thought about that behaviour or trait and jumpstart research and experimentation,鈥� she says.
Austral Ecology
