In the wet season, many frogs migrate to wetlands and other breeding sites to lay their eggs. In some species, such as the wood frog, many females congregate and lay their eggs communally, so it’s common to find large stretches of frog eggs floating in the same pool.
Most frogs lay large numbers of eggs as a natural way to counter the high mortality rates they experience in their early life stages. It is estimated that only 2% of frog eggs laid will survive to adulthood. The rest will be lost to predators such as newts and turtles – and also to the environmental conditions.
The large number of eggs laid by each frog is important for the survival of their species. If just a handful of eggs become adult frogs and live long enough to breed, the population of that species should remain stable.
How Many Eggs 22 Frog Species Lay
Most frogs are seasonal breeders, and will only lay eggs 1 to 3 times per year, usually in the spring or summer months after a heavy rain.
Over the course of the breeding season, a single frog can lay anywhere from a few hundred to as many as 20,000 eggs, depending on the species.
In some frog species, female fecundity (capability to produce offspring) increases with body size, so large females may lay more eggs than smaller females of the same species.
For example, most Cuban tree frogs only lay about 3,000 eggs, but large females can lay more than 15,000 eggs in one breeding season!
Below Is a Table That Shows Approximately How Many Eggs 15 Frog Species Lay at a Time.
Frog Species |
Scientific Name |
How Many Eggs They Lay (Approx.) |
| Wood frog | Lithobates sylvaticus | 1,000 – 3,000 |
| Pickerel Frog | Lithobates palustris | 700 – 3,000 |
| Northern Leopard Frog | Lithobates pipiens | 300 – 6,500 |
| American bullfrog | Lithobates catesbeianus | 6,000 – 20,000 |
| Green frog | Rana clamitans | 1,000 – 7,000 |
| Gray tree frog | Hyla versicolor | 1000 – 2,000 |
| Spring peeper | Pseudacris crucifer | 750 – 1,200 |
| American green tree frog | Hyla cinerea | 300 – 1,000 |
| River frog | Rana heckscheri | 6,000 – 8,000 |
| Australian green tree frog | Litoria caerulea | 200 – 2,000 |
| Northern cricket frog | Acris crepitans | 200 – 400 |
| Pacific tree frog | Pseudacris regilla | 400 – 750 |
| Crawfish frog | Lithobates areolatus | 3,000 – 7,000 |
| Pig Frog | Rana grylio | 6,000- 10,000 |
| Carpenter frog | Rana virgatipes | 200 – 600 |
| California red-legged frog | Rana draytonii | 300 – 4,000 |
| Cascades frog | Rana cascadae | 300 – 800 |
| Oregon spotted frog | Rana pretiosa | 250 – 1,000 |
| European common frog | Rana temporaria | 300 – 4,000 |
| American toad | Anaxyrus americanus | 2,000 – 20,000 |
| Cane toad | Rhinella marina | 8,000 – 35,000 |
| Asian common toad | Duttaphrynus melanostictus | 6,000 – 40,000 |
The Reasons Why Most Frogs Lay So Many Eggs
There are many reasons for frogs to lay as many eggs as they do.
1. Most Frogs Abandon Their Eggs After Laying Them
Most frog species do not show parental care for their eggs. After the mating is complete, both the males and females will leave the pond, abandoning the eggs.
This means the eggs are all on their own and are at the mercy of the environmental conditions. They are also easy meals for lots of predators.
2. Many Frog Eggs Are Lost to Predators
Frogs often lay eggs in open ponds and other water bodies – where predators accumulate over the course of the breeding season.
A large number of frog eggs are eaten by newts, turtles, leeches, dragonfly larvae, diving beetles, and other large water bugs.
It’s common for over 75% of frog eggs in a pond to be wiped out by predators before they hatch.
3. Frog Eggs Are at the Mercy of the Environmental Temperatures
Many frogs have extended breeding seasons and their eggs are exposed to a wide range of temperatures depending on the time of year when they are laid.
For frog embryos to develop normally, the surrounding water temperature should stay within a certain range.
If the temperatures fall beyond their preferred range, their development rate decreases, meaning they will take longer to hatch. And if the temperatures drop too low, the embryos can die.
On the opposite end, if the temperatures rise above the preferred range, the developing embryos may overheat which can lead to a very high mortality rate.
Since most frogs lay their eggs clamped together, the eggs closest to the outside of the egg mass are the most vulnerable to the elements – especially if they are exposed above the water’s surface.
4. Frog Eggs Are Vulnerable to UV-B Radiation From the Sun
Unlike reptile or bird eggs, frog eggs do not have a hard outer shell to protect the developing embryos. Rather, each egg has a jelly coat.
This jelly coat absorbs UV-B radiation, and also indirectly protects the eggs by virtue of its sticky texture and its tendency to accumulate a covering of pond debris.
However, the protection the jelly gives is only limited, so frog embryos are still vulnerable to certain doses of UV-B radiation.
Many frogs lay their eggs in well-shaded water bodies to protect the eggs from direct sunlight.
But some frog species such as the Northern red-legged frog (Rana aurora) often lay their eggs at the surface of the water, in direct sunlight.
Exposure to high levels of UV-B radiation can degrade the eggs of many frog species – and lead to lower hatching success.
High doses of UV-B radiation have also been shown to increase deformities in the embryos of some amphibians.
5. Frog Eggs Are Vulnerable to Pathogens
The eggs of many frog species are susceptible to infection from pathogens and fungi such as water mold (Saprolegnia).
The eggs are especially vulnerable to infection when they have been weakened by environmental stresses such as UV-B radiation or unusually cold weather.
Infection of frog eggs by fungi sometimes causes catastrophic losses of reproductive effort.
6. Most Tadpoles Do Not Survive Long Enough To Become Frogs
When the tadpoles hatch, they too will have very low survival rates.
Many tadpoles often hatch into crowded pools, and there will be intense competition for food and limited resources, meaning again the number of tadpoles will naturally thin out.
Many species of tadpoles are even known to eat smaller, vulnerable tadpoles – further reducing the numbers.
When the tadpoles develop into froglets and leave the water, only a few will live to adulthood and reproduce, – which can be as low as 1%
The rest will get eaten by predators such as snakes, raccoons, and a wide variety of birds.
Many frogs are also run over by cars, or indirectly killed by humans in other ways before, they ever get to reproduce.
Some Frog Species Only Lay a Few Eggs
Some frogs such as poison dart frogs (Dendrobatidae) and glass frogs (Centrolenidae), only lay a few dozen eggs at a time. The reason for this is, that they breed in more favorable environments – so, their offspring generally have higher survival rates.
Poison dart frogs and glass frogs are even known to protect their offspring – which improves the survival rates.
Generally, about 10 – 20% of all known frog species show some form of parental care. In these species, parental care may include the protection of eggs and/or tadpoles, transporting of tadpoles, feeding of tadpoles, or brooding of eggs.
For example, in many glass frog species, the mothers brood the eggs during the night the eggs are fertilized, and the fathers stay with the eggs to guard them for much longer periods.
Female horned marsupial frogs (Gastrotheca cornuta) carry their eggs in a pouch on their back until they hatch as fully developed frogs.
Darwin’s frogs ‘swallow’ their tadpoles, and put them in their specialized vocal sacs – then release them as fully metamorphosed froglets.
Sources:
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Garden wildlife health (2018). Spawn Failure in Amphibians (PDF)
Belden, L. K., & Blaustein, A. R. (2002). Exposure of Red-Legged Frog Embryos to Ambient UV-B Radiation in the Field Negatively Affects Larval Growth and Development. Oecologia, 130(4), 551–554. http://www.jstor.org/stable/4223204
Langhelle, A., Lindell, M. J., & Nyström, P. (1999). Effects of Ultraviolet Radiation on Amphibian Embryonic and Larval Development. Journal of Herpetology, 33(3), 449–456. https://doi.org/10.2307/1565642
Petrisko, Jill & Pearl, Christopher & Pilliod, David & Sheridan, Peter & Williams, Charles & Peterson, Charles & Bury, R.. (2008). Saprolegniaceae identified on amphibian eggs throughout the Pacific Northwest, USA, by internal transcribed spacer sequences and phylogenetic analysis. Mycologia. 100. 171-80. 10.3852/mycologia.100.2.171.
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