How Poisonous Is the Golden Poison Frog? Batrachotoxin Facts

What is batrachotoxin?

Batrachotoxin is a steroid-like alkaloid, and it is one of the most powerful natural poisons known. The name comes from the Greek word batrachos, frog. It was first isolated in the 1960s from the black-legged dart frog (Phyllobates bicolor), a close relative of the golden poison frog, and the frogs actually carry a family of closely related compounds, collectively called batrachotoxins.

The toxin is stored in glands spread through the frog’s skin, especially on the back. When a frog is stressed, attacked or injured, the glands release a milky or colorless secretion. A predator usually has to bite or mouth the frog to be poisoned, but toxin on the skin is also dangerous to anything that touches it with broken skin, the eyes or the mouth.

How does batrachotoxin work?

Nerves and muscles work by opening and closing tiny gates in their cell membranes called voltage-gated sodium channels. When a gate opens, sodium ions rush in and an electrical signal passes along the cell; the gate then closes so the cell can reset for the next signal.

Batrachotoxin binds to these channels and jams them open. Sodium keeps leaking in, the cells cannot reset, and nerve signals to the muscles stop working. The heart is affected especially badly, because its rhythm depends on the same kind of channels. The result can be:

• muscle weakness and paralysis
• an irregular heartbeat
• heart failure and death

No specific antidote is known. If anyone may have been exposed to a poisonous frog, the only right step is to seek emergency medical help immediately: call 911 in the US, 112 in the EU or 999 in the UK.

How much toxin does one frog carry?

The amount varies with location and diet, because the frog collects its toxins from food. Charles Myers, John Daly and Borys Malkin, who described the species in 1978, measured the toxins in wild frogs and found that they carried far more than their relatives. A commonly cited average is around 1 mg of batrachotoxins per frog, with the most toxic individuals they measured carrying close to 2 mg.

That may sound small, but batrachotoxin works at microgram doses, millionths of a gram. In laboratory mice, a lethal injected dose is only about 2–3 micrograms per kilogram of body weight. From such figures, the dose that could kill an adult human has been estimated at anywhere from a few micrograms to about 200 micrograms. A grain of table salt weighs roughly 60 micrograms, so even the high estimate is only a few grains’ worth.

Can one frog really kill 10 people?

Many books and websites say one golden poison frog could kill 10 to 20 people, or even two elephants. These numbers come from dividing the toxin content of a frog by an estimated human lethal dose, and they carry big caveats:

• No human lethal dose has been measured. It is extrapolated from mouse experiments, and animals react differently.
• Frogs vary. Toxin content changes from frog to frog and from site to site.
• Exposure is rarely complete. A person who brushes against a frog would not absorb its whole toxin load.

So the headline figure is a vivid way of saying that the frog is extremely dangerous, not a precise count. What is certain is that the golden poison frog carries by far the most batrachotoxin of any animal known, roughly 20 times as much as its closest relatives in some comparisons.

Which other animals carry batrachotoxin?

Batrachotoxin is remarkably rare in nature. It has been found in:

• Three Colombian frogs: the golden poison frog, the black-legged dart frog and the Kokoe poison frog (Phyllobates aurotaenia). Two Central American Phyllobates species carry only traces.
• Several New Guinea birds, such as the hooded pitohui, which carry it in their skin and feathers.
• Small melyrid beetles of the genus Choresine in New Guinea, which John Dumbacher and colleagues suggested in 2004 are the birds’ source.

Because the frogs lose their toxicity in captivity, scientists believe they too get batrachotoxin from their diet, probably from related beetles in Colombian forests, although the exact prey has not yet been identified. For the bigger picture, see why are poison dart frogs poisonous?.

Is anything immune to the golden poison frog?

Almost nothing eats adult golden poison frogs. The one well-known exception is a small South American snake, Erythrolamprus epinephelus, which resists several frog toxins, including batrachotoxin, and has been seen eating young golden poison frogs without harm.

The frogs themselves must also cope with their own toxin. How they do so is still debated: early studies suggested their sodium channels were resistant, while newer laboratory work points toward other protections, such as proteins that bind and hold the toxin.

How does it compare with other poisonous animals?

Pufferfish poisoning kills more people only because pufferfish are eaten; see are pufferfish poisonous?. More contenders appear in the list of the most poisonous animals.