How Do Poison Frogs Raise Tadpoles? Piggybacks and Egg Meals

Step by step: how strawberry poison frogs raise tadpoles

The strawberry poison dart frog of Central America is the best-studied example. Both parents help, but they do very different jobs:

1. Eggs on land: after courtship, the female lays about 3–5 eggs in moist leaf litter or on a leaf, and the male fertilizes them outside her body.
2. Father on guard: for about 10–14 days the male visits the clutch, keeps it moist by carrying water in his cloaca, guards it and removes fungus.
3. Piggyback ride: when the eggs hatch, the mother returns. The tadpoles wriggle onto her back, where they stick in a layer of mucus, and she carries them, one or a few at a time, up into the vegetation.
4. One tadpole per pool: she leaves each tadpole in its own tiny pool, usually the water caught in the leaf base of a bromeliad, though tree holes, puddles and even discarded cans are used.
5. Egg meals: every day or every few days she visits each pool and lays one or more unfertilized eggs for the tadpole to eat.
6. Becoming a frog: after about 6–8 weeks the tadpole transforms into a tiny froglet, stays near its pool for a few days while its tail is absorbed, then leaves.

The whole process, from egg to froglet, takes about two months. Our article on how tadpoles turn into frogs explains metamorphosis in more detail.

Why carry tadpoles to plants?

Most frogs lay hundreds or thousands of eggs in ponds and leave them. Poison frogs take the opposite approach: they produce only a few eggs and invest heavily in each one.

Laying eggs on land keeps them away from fish and aquatic insects, which eat huge numbers of frog eggs in ponds. Small pools in plants, called phytotelmata by biologists, are also relatively safe nurseries for tadpoles. A bromeliad may hold only a few spoonfuls of water, but it is unlikely to contain a fish.

The downside is that these tiny pools hold very little food. That is why egg-feeding evolved in some species, and why parents spread their tadpoles out. Poison frog tadpoles are often cannibalistic, and a larger tadpole may eat a smaller sibling if they share a pool.

Egg meals: how mothers feed their tadpoles

Strawberry poison frog tadpoles are obligate egg-eaters. Their mouthparts are reduced, and they cannot survive on algae, insect larvae or other food. A newly placed tadpole needs its first meal within about three days or it will starve.

The feeding visit is a little ritual. The mother backs into the pool and dips her vent into the water. The hungry tadpole stiffens its body and vibrates, a begging signal, and she lays one or more eggs, which the tadpole eats. She must remember the location of each of her scattered tadpoles and visit them regularly for weeks.

The eggs are more than food. Studies have found that mothers pass alkaloid toxins, the chemicals that make poison frogs poisonous, to their tadpoles through these egg meals. Tadpoles that are fed by their mothers carry alkaloids, while those deprived of egg meals do not, making them easier prey for spiders, insects and other frogs. Find out where these chemicals come from in why poison dart frogs are poisonous.

This care is costly. A mother feeds only about 4–6 tadpoles at a time, for 6–8 weeks, and she does not breed again during that period. Only about 5–12% of strawberry poison frog eggs develop into tadpoles, so the few that survive are worth the effort.

What do poison frog fathers do?

In the strawberry poison frog, the father’s role is shorter but still important. He guards and waters the eggs for a week or two, removes fungus and turns the eggs, and he can look after several clutches at once.

Males are not always kind to other males’ offspring, though. Researchers have seen territorial males eat eggs laid by rival males. Rarely, in captivity, a male strawberry poison frog has been seen carrying a tadpole, though whether he does this deliberately is unknown.

Parental care in other poison frogs

The family Dendrobatidae shows almost every kind of parental care found in frogs:

The mimic poison frog of Peru is especially remarkable. Pairs are monogamous, which is very rare in frogs. The father carries each tadpole to its own small pool, then calls near the pool to lead the mother there, and she lays a food egg for the tadpole. Scientists have linked this teamwork to the very small pools these frogs use, where food is so scarce that two parents are needed to raise a tadpole.

In the golden poison frog of Colombia, adults carry the tadpoles into the trees and drop them into bromeliads and water-filled tree holes, where the tadpoles feed on algae and mosquito larvae without further help.

How unusual is this among frogs?

Very unusual. Most frogs and toads give no care at all after laying their eggs. Carrying tadpoles is found in only a few frog families, and feeding tadpoles with unfertilized eggs is rarer still. It has evolved in some poison frogs, in a few tree frogs and in a small number of other species that breed in tiny pools of water.

That combination of guarding, piggybacking and feeding makes poison frogs some of the most attentive parents among amphibians, and a favorite study subject for biologists interested in how parental care evolves.