The University of Newcastle, Australia

The Aussie slug that can superglue its predators for days

Friday, 3 May 2019

Research scientists at the University of Newcastle have shown that the red triangle slug (Triboniophorus graeffei) produces a sticky defence mucus when disturbed that is strong enough to glue down predators for days. John Gould, a PhD candidate at the University, made the chance discovery when he came across an adult red-eyed tree frog (Litoria chloris) stuck to a fallen branch behind a red triangle slug in the Watagan Mountains in New South Wales. Their findings have been presented in a behavioural note published in Ethology.

“Finding such a large frog stuck to a branch and unable to free itself was very bizarre” says Gould, first author. “It was only when I saw the slug sitting near to the frog’s mouth that I started to wonder whether it was the culprit”.

The frog was brought back to the Conservation Research Group Laboratory at the University of Newcastle where it had to be prised from the branch by researchers after it showed no signs of improvement after more than a day. “If it was not brought back it would have remained stuck for days and possibly fallen victim to predation or dehydration” says Rose Upton, second author.

The slug was also brought back to the laboratory where it was discovered that touching the top surfaces resulted in the secretion of the sticky mucus. The research team propose that the frog tried to catch the slug and in doing so, caused the slug to release its sticky mucus as a form of defence. “Just based on the amount of mucus that was present on the frog, we don’t believe the frog simply became stuck in the slug’s locomotive trail, which would have only been a thin sheet of mucus” says Upton.

Though adhesive mucus secretions have been described in at least two other species of slug, surprisingly little evidence has been presented on its capacity to be used as a form of defence. “From what we can gather, this is the first natural observation of the use of adhesive mucus to incapacitate a predator in the wild” says Gould. Given that frogs are known to predate on slugs, this interaction between predator and prey species may be more common that suspected.

“What is unusual about this mucus is it is able to adhere in wet conditions, while gradually losing its stickiness as it begins to dry” says Dr. Jose Valdez, joint first author. This property is very exciting as it could make it useful as a biological binding agent in various industries. Another team is already developing a medical glue based on the adhesive mucus of a different slug species, Arion subfuscus.

What remains a mystery is the mechanism that prevents the slug from becoming stuck in its own secretions. “This is a question that remains unknown, not only for this species, but for all other species that have evolved an adhesive mucus for defence or predation” says Valdez. The research teams plans on examining these properties of the red triangle slug’s mucus in future studies.

Article ID: ETH12875
Article DOI: 10.1111/eth.12875

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