A Snake With Secrets
Rhabdophis tigrinus is a snake with secrets.
In Japan, the snake is fond of eating poisonous toads. But the snakes don’t die – even though they ingest quantities of toxins that would kill a human. Further, the females pass those toxins down to their babies. The snake has joined one of the few known species of vertebrate animals that become poisonous because of the poisonous prey they consume.
This phenomenon begs the question: If the poison doesn’t kill the snake, does it make the snake stronger?
“It doesn’t make them stronger but makes them better defended against prey,” said Al Savitzky, a professor of biology at Utah State University who has spent the last decade studying the snake in Japan, where it is known as the Yamakagashi. His work has involved colleagues and students in Japan as well as across the United States.
“These animals are taking in and storing massive amounts of this poison,” said Savitzky, who recently delivered a guest lecture about Yamakagashi to a group of students and faculty at the University of Arkansas.
“Their glands, which are sacs of fluid in the deep layer of their skin, are huge and just filled with these toxins and the quantities are extraordinarily high – relatively a lethal dose for humans,” Savitzky said. “They can store it in their glands more or less indefinitely.”
This ingestion and storage is known as toxin sequestration. There are numerous invertebrate species that ingest and deploy poisons as a defensive mechanism against their prey. Many are plant-eating insects, notably the monarch butterfly. This rarity is less well-known to occur among vertebrates, with only four recognized classes of species that can do it – poison frogs, two birds native to New Guinea, snakes that eat newts and now, thanks to Savitzky and his research partners’ work, snakes that eat toads.
Humans can handle the Yamakagashi without gloves because the snake doesn’t burst the poison out of its glands if it doesn’t feel threatened, Savitzky said. The poison is not absorbed through our skin, anyway.
“We’re still not sure how it expels the contents of the glands,” he said. “We’ve handled an awful lot of them and tried to get them to display their defensive behavior but they won’t do it. One theory is that they will expel the poison if a prey animal bites them, but we haven’t been able to observe it.”
But you don’t want this snake to bite you.
It has fangs in the rear of its mouth, which it uses to deliver weak venom to its prey, mostly non-poisonous frogs.
“If it bites and if it holds and chews it could cause people an awful lot of problems, and a few people have died from it,” said Savitzky, who has handled dozens of these snakes and has never been bitten. “Because they have this strong defensive chemical system, they don’t bite very much at all.”