Ants Discriminate Snake Friends and Foes

Ants share their nest with one snake, which may help protect them from another.

Posted Sep 17, 2019

Teppei Jono, used with permission.
Ants do not react to the presence of the Madagascar cat-eyed snake.
Source: Teppei Jono, used with permission.

In Madagascar, there is an ant with two very different relationships to two kinds of snakes.

Colonies of the ant Aphaenogaster swammerdami live in large, underground nests that have one entrance hole. Living in the same area is the blindsnake Madatyphlops decorsei, the largest blindsnake in Madagascar. Blindsnakes generally specialize in feeding on termites and ant broods by intruding into their nests.

The other snake in this story is the Madagascar cat-eyed snake (Madagascarophis colubrinus), which preys on various vertebrates—including blindsnakes. The local people of Madagascar call this snake the “Ant Mother” because it is often found in ant nests without being attacked by the ants.

Teppei Jono, now at the University of the Ryukyus in Okinawa, Japan, had heard the tales of the “Ant Mother” and seen the snake hanging out peacefully in ant nests. Because both the cat-eyed snake and the blindsnake are likely to enter ants’ nests, Jono and his colleagues thought the ants must be able to tell the difference between predatory and non-predatory snakes and respond differently to each species.

In a new study published in the journal Royal Society Open Science, Jono and his colleagues presented blindsnakes and cat-eyed snakes at the entrance of ants’ nests to see how the insects would react.

The researchers observed two highly specialized interactions between the ants and the snakes: Ants accepted cat-eyed snakes into the nest without attacking them, but, when presented with the blindsnake, the ants cooperatively evacuated their brood from the nest for protection.  

Given that the cat-eyed snake is one of the few known predators of blindsnakes in the area, the ants may protect their colonies against this blindsnake in two ways—evacuating in response to blindsnake intrusion and sharing their nest peacefully with a blindsnake predator.

Teppei Jono, used with permission.
Ants removing the brood from the nest in response to a blindsnake invasion.
Source: Teppei Jono, used with permission.

Jono and his colleagues say the cooperative transport of larvae and pupae from the nest is a highly specialized antipredator tactic against blindsnakes. Although several vertebrates, including anteaters, lizards, and blindsnakes, are known to feed specifically on ants, this is the first report of such predator-specific defensive behavior by ants in response to a vertebrate predator.

As to why the cat-eyed snake likes hanging out in ant nests, it could be that ant nests tend to remain at a constant temperature and humidity. In return for hosting the cat-eyed snake, the ants may receive protection from the predatory blindsnake.

“Some researchers have reported coexistence of snakes inside ants’ nests. However, these cases only occur during the winter, the non-reproductive season of ants, when they are inactive,” says Jono. “To the best of our knowledge, this is the first experimental evidence of snake-ant symbiosis in ants’ nests during the reproductive season of ants when they are aggressive.”

Jono and his colleagues suspect that such symbiosis is not unique to these ants and the “Ant Mother.” Several biologists have reported the presence of other reptile-eating snakes inside ants’ nests. These relationships could be more prevalent than previously thought, especially in areas where predation pressure by blindsnakes is severe. Scientists might just have to pay attention to local knowledge and keep their eyes open in the field to see them.

References

Jono, T., Kojima, Y., and Mizuno, T. (2019). Novel cooperative antipredator tactics of an ant specialized against a snake. Royal Society Open Science 6: 190283. Doi: 10.1098/rsos.190283.