Are Toads Poisonous? How Toad Skin Toxins Work in Defense

How toad poison works

A toad has no fangs and no sting, so it cannot inject anything. Instead its defense is passive. Its skin is packed with tiny glands, and on each side of the head, just behind the eye, sits a large swollen ridge called a parotoid gland. These glands store a thick, milky or creamy secretion.

When a predator bites or squeezes a toad, the secretion oozes out onto the skin and into the attacker’s mouth. It tastes extremely bitter and burns the lining of the mouth, so most predators drop the toad at once. Many young or inexperienced animals learn from one bad mouthful never to try a toad again.

Toads also help the defense along with their body language. A threatened common toad puffs itself up with air, rises on its legs and tilts its back toward the attacker. This makes it look larger and harder to swallow, and it points the parotoid glands straight at the predator’s mouth.

What is in a toad’s toxin?

The mix of chemicals varies between species, but most toads in the family Bufonidae, the true toads, produce two main types of compounds:

• Bufadienolides: steroid compounds that act on the heart. They are chemically similar to the heart drugs made from foxglove plants, and in large doses they disrupt the heartbeat.
• Amines such as bufotenine: substances related to the brain chemical serotonin, which can affect the nervous system and blood vessels.

The name bufotoxin is often used loosely for the whole mixture. It comes from Bufo, the Latin word for toad and the genus of the common toad. The secretion can also contain proteins and other substances that irritate the eyes and mucous membranes, the moist linings of the mouth and nose.

Common toads versus cane toads

Not all toads are equally dangerous. The difference lies in how much toxin a toad carries and how strong it is.

The common toad and the American toad produce enough toxin to make most predators spit them out, but for people the main risk is stinging eyes or a burning mouth after touching the face with unwashed hands.

The cane toad, the largest true toad, is in a different league. It has very large parotoid glands and a potent toxin, and every life stage is poisonous, from the eggs and tadpoles to the adults. In Australia, where cane toads were released in 1935, native predators had never met a toad before. Northern quolls, freshwater crocodiles, large goannas and some snakes have died after eating them, and pets that bite cane toads can also be poisoned. You can read more in Why are cane toads a problem in Australia?

Are toads dangerous to people?

For people, toads are dangerous only if the toxin gets inside the body. Touching a common or American toad is not harmful to healthy skin, but the secretion can sting the eyes, the mouth or broken skin. The simple rules are to watch toads rather than handle them, never to touch your eyes or mouth after contact, and to wash your hands well if you do touch one.

The serious cases involve swallowing the toxin. Human deaths are very rare and have mostly involved people who ate toads or toad eggs, or who licked or ingested toad secretions in the mistaken belief that they were a drug. If anyone swallows toad toxin or becomes unwell after contact with a toad, seek emergency medical help immediately: call 911 in the US, 112 in the EU or 999 in the UK.

Which animals can eat toads?

Toad toxin is a strong deterrent, but it is not perfect. Several predators have evolved resistance or learned to avoid the most toxic parts of the toad.

• Grass snakes in Europe eat common toads regularly with little apparent harm.
• Hognose snakes in North America specialize in toads and seem largely unaffected by their toxins.
• Hedgehogs, polecats, rats and mink are known predators of common toads.
• Otters often skin toads before eating them, leaving the toxic skin behind.
• Crows have been seen piercing a toad’s skin and eating its liver while avoiding the glands.
• Herons, buzzards and other birds of prey also take toads.

Scientists have found that some toad-eating animals, including certain snakes, carry small genetic changes in a protein that bufadienolides normally attack, a sodium-potassium pump in the cells. This makes them resistant to the toxin, and the same kind of change has evolved independently in several unrelated animals.

In Australia, some native animals have adapted to cane toads in other ways. Water rats and some birds have learned to flip toads over and eat the less toxic internal organs, and researchers have trained wild quolls and goannas to avoid toads by giving them small, non-lethal “toad sausages” that make them feel sick.

Myths and facts about toad poison

Myth: toads can give you warts. False. Warts are caused by a human virus, and the bumps on a toad are glands. Read more in Do toads give you warts?

Myth: toads spit or spray poison. Toads cannot spit, and the secretion usually comes out only under pressure, when the toad is bitten or squeezed.

Fact: toads are not the most poisonous amphibians. Brightly colored poison dart frogs carry far more powerful toxins. Toads appear on lists of the most poisonous animals mainly because of the cane toad.

Fact: toad tadpoles are poisonous too. That is why common toads can breed in ponds with fish, which learn to leave their tadpoles alone.