Snakes fed a diet of toxic toads become toxic too — and they seem to know it.

While many snakes make their own toxins, not all do. Japan’s tiger keelback snake () is one of a handful of species that can store toxins it acquires from its food.

Tiger keelback snakes are usually less than a metre long, an ideal meal for many birds and mammals. But they eat toxic toads and store the toxins in specialised organs on the backs of their necks called .

If a snake is threatened it arches its neck, making the nuchal gland area more prominent. A predator that bit the snake’s neck would probably get a jet of fluid from the glands straight in the mouth or face, which would be distasteful or even painful.

But not all keelbacks exhibit this defensive behaviour. Snakes from a toad-free island flee when attacked, rather than standing their ground. Now it seems the snakes know whether or not they are armed with toxins.

of Kyoto University, Japan, and of the University of Tennessee in Knoxville reared hatchling snakes from toad-free and toad-rich Japanese islands. The snakes were fed controlled diets containing toxic toads – or not.

When snakes from the toad-free island were fed toads, they started responding to threats with nuchal gland displays, rather than slithering away.

Know thyself

“So far as I know, this is the only example in terrestrial vertebrates where there is some indication that animals act as if they are aware of when they are toxic and when they are not,” says Burghardt.

Apart from snakes, plenty of animals acquire toxins from what they eat, but Burghardt says there is no sign they change their behaviour depending on what they have eaten. “Poison dart frogs in captivity are not fed the types of food that make them toxic, but their behaviour towards predators does not seem to have changed at all,” he says.

“It is remarkable that the researchers were able to demonstrate not only a difference in behaviour between these two populations, but that if you feed toads to toxin-free snakes, they are able to adjust their behaviour in a manner consistent with being chemically defended,” says of Utah State University in Logan.

How they know is an open question. The snakes could somehow monitor the amount of toxin in their glands. Alternatively, they might detect changes in the microbial community living in their digestive system, which would be influenced by toxin levels.

Journal reference: Journal of Comparative Psychology, DOI:

Take my lunch!

Sneaky beetles

Camouflaged fashionistas (Image: aphotomarine.com)

Species: Decorator crabs (superfamily Majoidea)
Habitat: Shallow waters worldwide

If there’s one thing we have in common with these crabs, it’s our keen sense of fashion. Many of us love to don new clothes, wear jewellery or get tattoos and piercings.

So it is with the decorator crabs. About three-quarters of over 900 species of crab in the family Majoidea decorate themselves, making them perhaps nature’s most fashion-conscious animal.

Although not the only animals known to decorate themselves, the crabs are the most well-researched group, according to a study reviewing such behaviours.

They improvise accessories using whatever is around, grabbing items such as seaweed, corals and sponges, and sticking them on their shells. Everything stays in place thanks to the hooked hairs, called setae, which line their shells and act like Velcro.

Blending in

But while we adorn ourselves to be noticed, crabs do it for the opposite reason: the decorations often provide camouflage against predators like fish and octopuses. Against the proper background, a decorator crab can blend in perfectly.

“The nice thing about being a decorator is that wherever you go, you can pull off the old decoration and stick on something new and quickly adapt yourself to whatever environment surrounds you,” says , an ecologist at the University of California, Davis. “If you’re a slow-moving, roving animal, being able to quickly adopt the coloration or background of wherever you are is likely very adaptive.”

For instance, the yellowline arrow crab (Stenorhynchus seticornis) tears a piece of seaweed in its claws and then chews it to make it rougher and more likely to catch on its shell. It backs up the camouflage by remaining still during the day and freezing when predators approach.

Repellent dress sense

Other decorator crabs are picky: any old outfit won’t do. They go for materials that are to predators.

“They are selecting decorations that make them toxic or bad to eat,” says Stachowicz.

The long-legged spider crab (Macropodia rostrata) and the longnose spider crab (Libinia dubia), for example, cover their shells with toxic seaweed. Stachowicz says you can trick these crabs into donning just about anything if you extract a chemical that fish find repellent from their preferred seaweed and paint it on to materials that they normally don’t use.

Yet others adorn themselves with stinging sea anemones. Predators might be able to detect the crabs, but will avoid attacking them.

Like all crustaceans, decorator crabs must shed their shells in order to grow, but they will often recycle their decorations after they moult. Carefully removing all the seaweed, anemones, sponges and other accessories from their old shell, they attach them to the new one when it hardens.

But some species outgrow the urge to accessorise altogether, possibly because they have fewer predators once they reach a certain size.

Journal reference:

Species: The Lusitanian toadfish (Halobatrachus didactylus)
Habitat: Bottom-dwelling, in rock crevices or muddy sediments on the floor of the

It whistles, grunts and croaks. The Lusitanian toadfish is for a fish. It makes at least five kinds of calls, and males even sing in choruses to attract mates with their boatwhistles – long, rhythmical, tonal sounds.

Now it seems the boatwhistle has another function: keeping intruding males away. Lusitanian toadfish can reach over half a metre in length and weigh over 2 kilograms. They have large, flat heads and wide mouths, giving them the toad-like appearance that they’re named after.

During the mating season, from May to July, males create nests under rocks and then sing to attract females. Males are territorial and they defend their nests from intruders. After mating, females leave their sticky eggs in the nest for the male to care for until the young are old enough to fend for themselves, at about three to four weeks.

Although boatwhistles were already thought to act as a keep-out signal to other males, there was no direct evidence of this. So , from ISPA University Institute in Portugal and her colleagues decided to test this hypothesis by muting male toadfish and seeing what happened.

Shushing a noisy fish

Lusitanian toadfish call by contracting muscles on their swim bladders, which releases air. Different sounds result from different contraction rates. Think of it as an underwater bagpiper.

Amorim and her colleagues muted some toadfishes by cutting and deflating their swim bladders under anaesthesia. These fish could still contract their muscles, but couldn’t make any sound.

They found that the nests of muted males were more likely to be intruded upon, probably because they were unable to sing. Their results suggest that boatwhistles are effective keep-out signals, reducing the risk of territorial intrusions and therefore nest takeovers.

“Boatwhistles are a cheap way to exclude intruders without engaging in a fight,” says Amorim. “Seeing that a nest is occupied is not as effective as hearing that there is a male in the nest eager to defend its territory.”

Some aspects of toadfish boatwhistles, such as frequency and pulse interval, are associated with the size of the fish, meaning that others can use it to assess the quality of potential mates or the fighting ability of rivals.

The Lusitanian toadfish is not unique in making underwater noise. Herrings fart to find each other in the dark, clown fish chatter by clacking their jaws together to warn intruders to stay away and another species of toadfish cries like a baby.

Journal reference: Journal of Experimental Biology , DOI: