Are Frogs Cannibals?

While frogs may look very cute in nature photography, you may be surprised to learn that frogs engage in cannibalism. Frogs even engage in filial cannibalism, meaning that some adults will not hesitate to eat the young of their own species, including their offspring.

As a general rule frogs are cannibals and engage in cannibalism. This is especially true for larger frog species like Cane Toads and American Bullfrogs. Larger Frogs typically eat frog eggs, tadpoles, froglets, and smaller adult frogs including their own species and offspring.

Let’s have a look at the various aspects and evidence of frog cannibalism as well as uncover the reasons why tadpoles, froglets, and adult frogs may eat other frogs. We’ll also consider negative and positive side effects of cannibalism on frog populations and what this means if you have a pet frog.

Adult Frogs May Eat Their Offspring

Adult frogs are known to eat their offspring including their own frog eggs and tadpoles. Adult frogs generally engage in this behaviour when other sources of food are scarce, due to fatigue after laying eggs, or to control the population.

African Clawed Frogs have been extensively studied and been observed eating not only its own tadpoles, but other African Dwarf Frogs. Cane Toads are an invasive species in Australia and Florida and are known to eat their offspring as well as smaller native frog species.

Adult frogs may engage in cannibalism for the following reasons:

  • Lack of other readily available food sources
  • Fatigue after laying eggs
  • Population control

To test the significance of cannibalism, different frog species were placed into tanks together at various life cycles stages. Careful measurements revealed that African Clawed Frogs preferred to feed on the other species (Thorp et al, 2018).

However, frogs generally avoid eating other Anura when other food is available since the nutritional value of tadpoles and frog eggs is not particularly high (Zoologger, 2014). Since there are better food sources in the wild, frogs tend to avoid cannibalism when possible.

Tadpoles May Eat Each Other

Frog tadpoles are known to engage in cannibalism, notably when other food sources are lacking, are poor in nutrients, due to lack of space for development, or due to competition for resources. Competition may be the main reason why tadpoles feed on other smaller, vulnerable tadpoles.

Tadpoles will eat each other, notably when they are starved or if the population densities are high. Unless their diet leads to starvation, cannibalism may occur as a result of competition rather than be based on the quality of available food (Jefferson et al, 2014).

Tadpoles may engage in cannibalism for the following reasons:

  • Lack of food
  • Lack of space
  • Starvation
  • Reducing competition
  • Population control

The decomposition process due to the death or attack of other tadpole lets off certain smells act as alarm cues that warn other tadpoles when cannibalism is taking place and may deter potential cannibals from feeding (Jefferson et al, 2014).

However, further studies revealed that cannibalism is not the basis for a good diet. Given alternative food sources, tadpoles will prefer almost anything else over fellow tadpoles.

If you are raising tadpoles in captivity, be sure to provide them what tadpoles need to survive: chose the right kind of water, enough space and shelter to flourish, and of course be sure to feed them the right foods depending on their level of development to avoid cannibalism.

Larger Frogs Eat Smaller Frogs

Larger frogs are known to eat smaller frogs in the wild and in captivity. This is why it is generally recommended to avoid keeping two pet frogs of different sizes together in the same vicinity.

Adult frogs are carnivores that feed on insects and small mammals depending on the species and their size. Frogs and other amphibians exhibit tendencies to cannibalism, particularly when they cannot satisfy their food needs through other food sources.

One study found that for every millimetre increase in the snout to vent (SVL) length the observed frog, the species is 2.8% more likely to eat other anurans, and invasive frogs are 40% more likely to eat anurans (Measey et al, 2015).

Large invasive frogs that live in forests with high anuran diversity are most likely to have a higher proportion of anurans in their diet.

Measey et al, 2015

Frogs have long been known to eat anything smaller than them, including their own offspring, even as tadpoles. The combination of high population density, food scarcity, and evolutionary reality have seen many frog and toad species converge towards cannibalism. Cannibalism can have both positive and negative side effects on frog populations.

Side Effects of Frog Cannibalism

Frog cannibalism can have positive side effects such as population control and survival, but also have negative side effects such as reduction in native species when invasive species feed on local populations.

Positive effects of frog cannibalism:

  • Population control
  • Survival
  • Reduced burden on the ecosystem with high populations

Cannibalism makes evolutionary sense to frogs in certain situation where the population density is high. Juvenile and adult frogs may find that eating the young gives them necessary energy to grow while controlling the local population. This has the additional benefit of removing another burden on the ecosystem since tadpoles will grow up to consume resources.

Negative effects of frog cannibalism:

  • Reduction in native species
  • Reduction in frog populations when they are already scarce

One of the main issues of cannibalism due to invasive species is the reduction of native frog species. In Australia and Florida, the invasive cane toad has few natural predators. Field work has demonstrated that tadpoles can detect nearby frog eggs, likely through smell. Cane toad tadpoles may then cannibalize native specie’s eggs. And since these toads generally reproduce twice per year with up to 30,000 eggs, they are reducing the local frog populations.

More About What Frogs Eat

Learn more about what and how frogs eat in these articles on our blog:

Sources

Jefferson, D.M., Hobson, K.A., Demuth, B.S. et al. Frugal cannibals: how consuming conspecific tissues can provide conditional benefits to wood frog tadpoles (Lithobates sylvaticus). Naturwissenschaften 101, 291–303 (2014). https://doi.org/10.1007/s00114-014-1156-4

Measey GJ, Vimercati G, de Villiers FA, Mokhatla MM, Davies SJ, Edwards S, Altwegg R. 2015. Frog eat frog: exploring variables influencing anurophagy. PeerJ3:e1204 https://doi.org/10.7717/peerj.1204

Thorp, Corey & Vonesh, James & Measey, John. (2018). Cannibalism or congeneric predation? The African clawed frog, Xenopus laevis (Daudin), preferentially predates on larvae of Cape platannas, Xenopus gilli Rose & Hewitt. African Journal of Ecology. 57. 10.1111/aje.12577.

Zoologger: Cannibal tadpoles eat the competition, New Scientist, Volume 222, Issue 2965, 2014,
Page 16, ISSN 0262-4079, https://doi.org/10.1016/S0262-4079(14)60762-4.