1. These are not the frogs you’re looking for
On the savannahs of West Africa, stink ants (Paltothyreus tarsatus) are well known for their aggressive foraging raids, in which huge numbers of ants hunt together for larger insects and even vertebrate animals as large as frogs and rodents. The ants are just as dangerous at home, and will defend their colonies and kill intruders with powerful bites and venomous stings.
They don’t seem like they’d make good roommates, but they’re exactly what the West African Rubber Frog (Phrynomantis microps) is looking for. The ants' nests are nice and humid and keep the frog’s skin moist during the long dry season, and the ferocity with which the ants guard their home means the frog doesn’t have to worry about other predators.
If any other frog tried to move in to a stink ant colony, it would be attacked and stung immediately, but the ants seem to ignore the Rubber Frog completely. This is because the frog uses what’s sort of a chemical Jedi mind trick. Most social insects like ants use chemical cues to communicate and recognize each other. To get along with its potentially less-than-gracious hosts, the frog coats its skin with compounds that tell the ants, in their chemical language, to leave it alone.
The frog’s skin secretions are an allomone, an animal-produced chemical signal that benefits the sender by altering the behavior of the receiver. Some allomones work as repellants that keep predators away. Others attract unwitting prey. The one used by the Rubber Frog seems to work as what scientists call an appeasement substance. It curbs the ants’ aggression and delays their attack by saying, Nope, don’t mind me—I’m not making trouble.
The allomone even works when it's not the frog wearing it. When researchers covered mealworms and termites with skin secretions from a Rubber Frog and offered them to ants, the ants ignored the treats for several minutes until the secretions dried and the effect wore off.
2. Looks like a silverfish, smells like an ant
The silverfish Malayatelura ponerphila also lives among ants in their nests, but takes a slightly different approach to blending in. Instead of appeasing its hosts, M. Ponerophila disguises itself as one of them.
Because the chemical signals the ants use to communicate are so widely distributed through their colonies, say biologists Freddie-Jean Richard and Jim Hunt, each colony takes on a specific odor that help its members tell nestmates and intruders apart. M. Ponerophila borrows this chemical uniform by sneaking into a colony and rubbing its body against defenseless larvae, pupae, and callows (immature ants) to pick up the compounds that form the colony’s signature odor.
As long as a silverfish keeps this scent on itself, it gets access to shelter in the nest and the ants’ food stores, without having to contribute anything to the colony. Like stink ants, though, the army ants that M. Ponerophila lives with in Malaysia are very aggressive, and silverfish that are separated from their scent supply and recognized as intruders are frequently attacked and killed.
3. Sheep in wolf’s clothing
Chemical trickery isn’t just for sneaking into ant colonies. Two different squirrel species are known to chew on rattlesnake sheds and then lick themselves, anointing their fur with odor compounds from the old skin. As with the silverfish, this gives the squirrel a chemical disguise that helps it hide its own squirrel-y scent from snakes.
The rattler perfume also seems to help the squirrels by changing their behavior. Researchers noticed that squirrels that had recently applied snake scent to their fur groomed themselves more and rested less. The squirrels, the researchers thought, had fooled themselves a little with their disguise, too, and were going through a stress response to the scent of a predator—which helped make them more alert in case an actual snake showed up.