Puff adders, venomous snakes found throughout Africa, have a secret weapon to avoid predators and surprise potential victims: They can hide their scent. A new study published in Proceedings of the Royal Society B, finds that particularly scent-oriented predators like dogs and mongooses cannot detect the smell of the snakes.

Researchers from Wits University in South Africa trained dogs and meerkats to recognize the smells of a variety of snakes. The animals were trained to sniff a target scent, then identify that same scent in a lineup of other smells. While the animals could identify the scents of other snakes at rates higher than could be attributed to chance, they were terrible at identifying the scents of either wild or captive puff adders. The study’s authors suggest that puff adders' ability to hide their scent might come from their low metabolic rate, which might allow them to emit fewer odorants.

Puff adders are ambush predators, meaning they lie in wait until something delicious walks by. This leaves them fairly open to being eaten themselves, since they stay in the same place for long periods of time. Ambush predators often use camouflage to stay hidden, but plenty of predators are keen sniffers who won’t be fooled by camouflage. 

Crypsis—the ability of an organism to avoid detection—is often a visual adaptation, and occasionally an aural one. Camouflage helps animals blend into the background, and being nocturnal allows them to hide in the darkness. Mimicry helps them pose as another species. However, this is rare proof of chemical crypsis as an animal’s anti-predation strategy. Though various forms of scent-masking have been found in other species, like filefish and parasitic mites, the researchers contend that this is the first evidence of chemical crypsis as a defense mechanism by a land-based vertebrate. But since puff adders are not the only ambush predators left vulnerable by their relative immobility, it’s possible other animals with the same predation strategy might use this technique, too.

[h/t: The Guardian]