Southern toads recognise and avoid an aggressive invasive ant species in the US.
“Our study is the first to reveal that an amphibian, the southern toad, views fire ants as a predator,” said the study’s lead researcher Andrea Long from the University of Florida, Gainesville, US.
Details of the findings are published in the journal Biological Invasions.
Red imported fire ants (Solenopsis invicta) – also known as RIFA – predate young amphibians, and their venom is thought to cause death or injury to adult southern toads (Anaxyrus terrestris) that try to eat them.
The invasive ants are similarly venomous to some native fire ants, but they are more aggressive.
RIFAs, which are native to South America, were introduced to the southeastern United States in the 1900s, and have been linked with the decline of amphibians such as the endangered Houston toad (Bufo houstonensis) and the marbled salamander (Ambystoma opacum).
Scientists in the US tested the theory that southern toads would distinguish between dangerous invasive fire ants, and non-lethal native ants.
The team recorded juvenile toads’ actions on video in an arena shared with a closed tea strainer at one end containing either fire ants, native pyramid ants or no ants.
The idea that fire ants could elicit such a strong anti-predator response in southern toads, after being on our study site for about 50 years, is fascinating
The amphibians spent 35% less time in the half of the arena that contained the fire ants. And they moved around more when the species was present.
When native pyramid ants were present, the toads made several attempts to eat them, striking at the tea strainer. But this only happened once with fire ants.
The results suggested that toads distinguished between the dangerous RIFAs and the harmless pyramid ants, and adapted their behaviour depending on which species they were near.
“The idea that fire ants could elicit such a strong anti-predator response in southern toads, after being on our study site for about 50 years, is fascinating,” said Ms Long.
The toads might be able to recognise the dangerous ants by sight or by chemical cues, or a combination of both, the researchers suggest.
Animals that have not co-evolved with a particular predator may lack the ability to avoid danger and can be especially vulnerable.
“Without developing anti-predator behaviours to cope with an invasive predator, native prey may experience greater population declines and some populations may go extinct,” the researchers wrote in their paper.
But although the toads’ predator avoidance tactics around red imported fire ants enhance their chances of survival, too much movement may have a negative effect on their food-finding and reproductive success, according to the study.
“As species invasions increase globally, understanding how native species cope with novel pressures is increasingly important.”
You can also follow BBC Earth on Twitter, Facebook and Instagram.