If you’ve ever seen the bizarre aerial acrobatics that is gastropod sex, you’ll likely be aware that slugs can lower themselves on a kind of mucus bungee rope to keep them off the ground while they get their rocks off. This kind of mucus acts more like a winch, only being tethered at one end, but a recent study published in the journal Austral Ecology details the fortuitous discovery of an entirely new use for mucus among these slimy slitherers.
Captured on camera by study author John Gould of the School of Environmental and Life Sciences at the University of Newcastle, Australia, a slug can be seen traversing a kind of mucus bridge that's tethered at both ends. The slug was riding solo, so the spider-like locomotion of using a thread to move between surfaces wasn’t with a goal to procreate, simply a means of getting to the ground.
“Slugs more commonly move across surfaces by producing a thin film of mucus which they glide over, maintaining contact with the surface at all times,” wrote Gould in an email to IFLScience. “However, to move through the air, it is apparent from my observation that some slugs have the capacity to excrete a single mucus line which they are then able to glide down. To this extent, the slug is forming its own surface in the air which it can then exploit for locomotion.”
The finding was stumbled across by accident, as Gould and colleague Jose W. Valdez found the curious critter while conducting field surveys for an endangered species of frog. Gould first thought he’d come across a spider hanging from silk, but on closer inspection realized it was a striped field slug (Lehmannia nyctelia). Even more curious was that the mucus thread wasn’t being influenced by the weight of the mollusk sliding down the slimy pole. If you look closely, you can see how stable the thread remains throughout the slug’s journey, as the small rocks stuck to the bottom of it don’t move.
“What really interests me is the decision making process that causes a slug to exploit this form of locomotion over the more commonly exhibited behaviour of gliding over surfaces on a film of mucus,” continued Gould. “We suggest that creating a new surface in the air that acts as a vertical bridge may allow for a much more rapid descent from heights. This could have energy saving and anti-predation benefits.”
The duo next hopes to observe the behavior under more controlled conditions as a means of determining the chemical properties of the mucus thread – which appears to be remarkably strong and stable in supporting a slug’s vertical dismount without breaking.
Now if you'll excuse me I'm off to option a Spiderman spin-off series.