Frogs return to the pond to mate in Spring and spawn
Frogs in Spring:
The males return first to the pond where they were raised and attract the females to them by croaking. They mate in shallow areas of the pond amongst plant growth.
Once he has attracted his female he will grip her from above with his forelimbs in an embrace called ‘amplexus’. The female will then lay spawn which is fertilized by the male as it is released. The female will use plant growth on shallow shelf areas to support herself during this process as she can be suffocated or drowned. The mating can last for days and more than one male can mount one female while she is laying spawn.
Each female usually produces one clump of frog spawn in a season usually in warm days in March. Frog spawn is laid as lumps about the size of a tennis ball made up of jelly and eggs on shallow shelf areas which will swell to grapefruit size as they mature and float to the water surface so that many can merge to look like one jelly mat.
Freshwater Habitats Trust (formerly Pond conservation) ask pond owners to take part in the Big Spawn Count every year to see how many clumps of spawn appear in your pond so they can see how many breeding females are reported.
Big Spawn Count results show:
- The timing of spawn being laid depends on the outside temperature and can vary by 2-3 weeks
- Up to 5mx5m appears to be the optimum size for the water area with the pond shelved to produce areas of shallows and the pond in the sun. The average number of clumps of spawn in a 5mx5m pond was 14.
- A smaller pond of 1mx1m had, on average, 7 clumps of spawn (or 7 visiting female frogs whichever way you want to look at it).
The area around the pond should be a well planted habitat giving protection and hiding places to get the best numbers of frog visitors.
Over the weeks of spawning many frogs will appear in the water and a mass of movement and frog spawn can be the result.
Our pond had over 40 frogs in it at one point and created at least 15 balls of spawn which soon merged together as a swollen mass of jelly that would protect the eggs. The juvenile frogs not yet capable of mating (3 years old) may appear in the pond too.
Frog spawn survival:
Froglife (the wildlife charity for conservation of amphibians and reptiles) advise that frog spawn is not taken from one pond to another to help control the spread of invasive pond plants and amphibian diseases.
The adult female lays several thousand eggs to allow for huge losses – each in a clump of jelly with dark brown-black centres. A clump of spawn will sit half submerged under the water and half exposed to the air and be vulnerable to being killed by overnight frosts. Very cold weather can interrupt spawning – a second batch of frogspawn may appear in your pond once the cold weather subsides.
Dead eggs will have grey or white centres. In a light frost only the spawn closest to the surface will be killed the rest may survive as they are insulated from the cold in the centre of the clump. If a small amount of spawn has died leave it in the pond and it will break down or get eaten by other creatures.
Around three weeks after spawning the tadpoles hatch out from their eggs. They are each about 12mm long and brown in colour. They will feed on the old jelly mass and any algae which is growing on it. You can supplement their early food requirements with a vegetable based food – particularly important in a new pond – at first use Early stage – Tadpole food.
Frog tadpoles in Summer:
Once they start to develop legs, tadpoles change from being vegetarians to carnivors. Most established ponds will have enough food for the tadpoles to develop to maturity but in a new pond or with a large number of tadpoles in your pond you can supplement with both early stage (vegetable based) or late stage (high protein) tadpole foods.
Many tadpoles are eaten in Spring – up to 90% of the eggs, tadpoles or froglets in the pond are lost to predators (dragonfly larva, water boatmen, snakes or birds) as they swim together in the warm shallow waters at the edge of a pond.
They need as much cover from plant leaf as possible so they have somewhere to hide from these predators. This would include Myosotis species, Veronica beccabunga and in a larger pond area – Mentha aquatica, Menyanthes trifoliata and Rorippa nasturtium-aquaticum.
Numbers of one species will control another until they balance with each other eg newts are a predator of frog tadpoles especially in the weeks immediately after frog spawning when adult newts are in the pond laying their eggs. And late stage frog tadpoles can eat young newts when the frog tadpoles are in the carnivore stage.
Adult frogs can be affected by Frog red leg – ranavirus – on hot days between June and August at temperatures above 25°C. To identify you have this problem – you will find a large number of dead frogs in a short space of time with the frogs often thin and lethargic before death.
Affected frogs may appear with:
Abnormal wasting (emaciation).
Redness of the skin (erythema).
Skin ulcers or sores.
Bleeding (systemic haemorrhaging), especially from mouth/anus.
Breakdown of limbs (limb necrosis).
Frogs in Winter:
Frogs may live in the pond over winter as they can breathe through their skin but most will leave and spend Winter under logs or sheds, in compost heaps or any other damp hiding place they can find.
Most frogs return to the pond of their birth from Winter hibernation to mate and produce frog spawn in Spring.