By Dr. Becker
Poison dart frogs, also called poison arrow frogs, are known for two things — their striking appearance and their poisonous venom. The two go hand-in-hand, as the frogs' brilliant colors serve as a warning of their extreme toxicity.
One species, the golden poison dart frog, is only 2 inches long but contains enough venom to kill 10 people.1 It's said that even holding one in your hand could be fatal.2 The venom's deadly effects were well known to the indigenous Emberá people of Colombia, who coated the tips of their blowgun darts with the poisonous substance.
A curious feature about the frogs, however, is that while they're formidable poisonous creatures in nature, they tend to lose their toxicity when raised in captivity.
Poison Dart Frogs Raised in Captivity May Lose Their Poison
The reason why poison dart frogs raised in captivity tend to lose their poisonous venom is attributed to changes in their diet. The poison is not produced in the frogs, but rather comes from their diet and is then secreted from their skin.
In the wild, poison dart frogs feast on certain ants and beetles that contain toxic steroidal alkaloid molecules (which they either produce themselves or acquire via plants they eat). These toxins are responsible for the poison's toxic effects. They affect the nerves and muscles, leading to cardiac arrhythmia and heart failure.
When the frogs eat the ants or beetles,3 they store the toxic alkaloids in their glands and then secrete it as needed.
Valerie C. Clark, Ph.D. a then graduate student in chemistry at Cornell University in Ithaca, New York, authored a study in 2005 that identified some of the alkaloid-containing insects consumed by poison frogs.4 She told National Geographic:5
"It's really smart for frogs … It gives them a nice defense, and they don't have to waste energy biosynthesizing and making [the toxins] on their own …
And they're stealing it from their diet, which means they are also able to eat toxic insects other frogs reject as distasteful … They're able to exploit a whole other niche."
When raised in captivity, however, the frogs aren't fed these toxic insects, instead munching on non-alkaloid fruit flies, mealworms, crickets and termites. They therefore lose their source of poisonous venom and eventually turn harmless.
Are Wild Poison Frogs Losing Their Toxic Edge?
Separate research conducted by Clark and colleagues found even wild poison frogs may be losing some of their toxicity. Frogs with a greater diversity of alkaloids in their skin are generally most lethal to predators. However, the researchers found different make-ups of alkaloids in frogs from different regions.
Specifically, frogs from pristine forest areas had about 30 different alkaloids in their skin while those living in disturbed habitat had only about 12.
Even those living near a roadside in a moderately disturbed habitat had only 15 different alkaloids on average.6 Writing in the Journal of Chemical Ecology, the researchers noted:7
" … [F]rogs from the most pristine locality had the greatest number of alkaloids, whereas individuals from the most disturbed localities had the least.
In a comparison of frog alkaloid profiles over a 10- to 14-year period, alkaloid turnover, and thus presumably alkaloid-source arthropod turnover, was high in a disturbed locality and low in the pristine primary forest locality."
The reduction in alkaloid variety is likely due to a reduction in arthropod species (insects) in the frogs' diets.
Poison Frog Fun Facts
Poison dart frogs can live from 3 to 15 years in the wild, a lengthy lifespan that's attributed largely to their lack of predators. The only known natural predator of these frogs is a snake called Leimadophis epinephelus, which is resistant to their poison.8
The frogs have an elaborate mating ritual, which includes male frogs vocalizing to attract females. The females deposit eggs on leaves and the males check on the eggs for two weeks until the tadpoles hatch.
At this point, the male carries the tadpoles on his back (held in place via a mucus secretion) and takes them to a watery spot to continue development. This includes small ponds, water collected in coconut shells or even water inside a bromeliad plant.
The tadpoles are then left on their own to develop into frogs (a process that takes about three months). If researchers are correct and wild frogs continue to become less toxic due to habitat disturbances, it's possible that other species could catch on and start to prey upon the newly defenseless frogs.
This could have dramatic ramifications for the surrounding ecosystems as well as impact their medicinal uses. Venom from poison dart frogs has been used to develop a compound that might act as a painkiller in humans and other medical uses for the venom are also being explored.
If you opt to keep amphibians as pets please only buy ethically raised, captive-bred specimens. Purchasing wild-caught animals contributes to ecologic decline and these animals often die in captivity from stress.