Meet 4 animals who use chemical deception to camouflage their smell

In an eat-or-be-eaten world, camouflage matters. A chameleon becomes a bump on a log. A praying mantis turns into a delicate orchid.

But camouflage doesn't have to be only about what the eyes see. A lot of communication on earth actually occurs by scent, not sight, in the form of released chemicals like pheromones. It's just that we humans, with our inferior senses, are mostly oblivious to it.

In fact, many different animals rely on "chemical deception" to keep predators or prey from following the scent trail to the truth. Some hide by blending in with background smells, while others mimic the scent of something else. There are even animals that produce essentially no (detectable) levels of scent!

So get ready to meet four animals you'll have a hard time finding if you're just following your nose.

Puff adders

Abundant across Africa, these venomous vipers hunt their prey by ambush. But lying around in the same spot for weeks could, in turn, make the snakes vulnerable to becoming dinner, especially to predators with a good nose. So how do they stay safe?

During one experiment, researchers from South Africa's Witwatersrand University noticed the puff adders they were tracking went undetected by dogs and tame mongooses, which would walk right over the snakes without spotting them.

To test the idea that puff adders can't be sniffed out, the team trained dogs and meerkats to recognise and then match specific scents from an olfactory buffet. The animals had little problem picking out the smells of five other snake species (and even freshly shed puff adder skins), but live puff adders totally stumped these sharp-nosed detectives (check out this video for more). Clearly, even porcupines will parade right across puff adders without a backward glance:

Credit: Wits University

Pirate perch

Here's a fun fact about the pirate perch: as this freshwater fish ages, its anus moves up its body until it's right under the throat! As for the mouth, you'll find that in the usual location – and these voracious fish will gobble up pretty much anything that fits inside, mainly aquatic bugs and small fish in swamps and ponds across the US (in aquariums, they'll also happily cannibalise their tank-mates, which is how the species earned its buccaneering nickname).

Unlike other fish, pirate perch can swim under the radar of their favourite prey. Tree frogs, aquatic beetles and mosquitoes normally avoid laying eggs or colonising areas anywhere near fish (even non-threatening ones) – but they don't seem to avoid the perch. In one series of experiments, researchers showed that beetles and frogs didn't seem at all aware of the lurking perch, suggesting these fish have a way of chemically masking their presence.

“To be honest, it never ceases to amaze me how clear the lack of response is to pirate perch,” reported University of Mississippi ecologist Bill Resetarits, who conducted the studies.

Giant geometer moth caterpillars

Simply looking like a bumpy stick isn't enough for these caterpillars. Taking camouflage to the next level, the critters incorporate elements of whatever plant they're munching on right into their exoskeleton ... and end up smelling like a stick too.

The caterpillars' strategy works like a charm to fool hungry ants. Blissfully ignorant, the insects go marching all over the moth larvae – as long as the caterpillars' scent matches the plant they're on. Plop them on a plant they haven't sampled, and the ants attack.

Harlequin filefish

A flashy teal fish speckled with orange, the harlequin filefish lives among coral reefs in the Indian and Pacific oceans. Its polka-dot pattern certainly helps with disguise, but the fish also fends off potential predators by eating – and smelling – like the Acropora coral it calls home.

In a 2014 study, scientists found that some coral-dwelling crabs couldn't even tell the difference between the smell of Acropora-eating filefish and the coral itself. Meanwhile, predatory cod seemed totally indifferent to the harlequins when the fish were presented alongside the coral they ate (no matter the coral type).