Each clump of spawn is laid by a different female frog
Nature on our doorsteps: Frog spawn
Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures.
Frog spawn is the term given to the mass of eggs laid by a female frog.
From January until the end of March, adult male and female frogs make their way back to the ponds in which they themselves developed, three or four years earlier.
As the breeding female releases her eggs into the water, the male frog fertilises them.
The mass of eggs sticks together, and there can be more than a hundred eggs in a single clump.
The individual eggs themselves appear as little black dots surrounded by a jelly-like substance.
This jelly immediately begins to absorb water and swell in size, and its main function is to protect and provide nutrition to the eggs as they develop.
The jelly prevents the eggs from drying out and it provides a barrier against harsh environmental conditions and most predators.
Male frogs will wait close to lain spawn, waiting for other females to arive
Frogs will often scramble over clumps of spawn to lay their eggs amongst them, rather than on the outer edges of the mass.
The reason behind this behaviour appears to be that the water is warmer in the middle of the mass of egg clumps when compared to around the edges.
Tadpoles develop faster in warmer water, so the eggs that are laid in the middle do better.
The clumps that are laid in the middle are also furthest from potential predators.
These include fish, water birds, water beetles, and the larvae of insects like dragonflies.
Free-living flatworms living in the pond will also nibble on the little protein-rich eggs and cause them to fail
The jelly around the egg contains proteins and other nutrients which the developing egg absorbs, supporting it as it develops and grows.
When the tadpole finally emerges from the jelly, it will stay around the remains of the sac for a while, where it continues to eat it until it is ready to feed on pond algae and plants.
