NATURE NOTES - The lives of frogs

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IT’S a couple of weeks since I saw my first frogspawn and now most of our local ponds have got their nice new ‘dollops’.

Frogs lay their spawn in shallow, still water, forming large clumps of eggs that rapidly swell up as they absorb water. Toads tend to spawn in deeper water forming ropes of eggs, which wind around plant stems.

Believe it or not, from a clutch of 2,000 eggs, on average only 5 adults will survive long enough to breed. The rest will form part of the diet for fish, newts, birds, water beetles, and even other tadpoles.

The metamorphosis from tadpole to adult not only includes the visible changes in body structure, but also a change in feeding habits from vegetarian to ferociously carnivorous. However, some tadpoles never complete the change, tadpoles of up to 12cm in length have been found.

This permanent “hormonal teenager” phase is associated with too low a water temperature. That would explain a lot – I know a few ‘people’ who must shower in cold water every morning.

The frog’s diet consist mainly of insects, small animals like earthworms, small fish and spiders. Frogs have a sticky tongue. To catch an insect, the frog flips out its tongue rapidly, gets the insect and then pulls in its tongue with the insect stuck on.

Frogs will swallow their prey whole because they only have teeth in the upper jaw. Doesn’t do much for chewing! Frogs hunt mostly at night.

Most years I get phone calls from concerned owners of garden ponds panicking about the swarm of frogs that are writhing about in their ponds.

Sometimes garden ponds can seem to be over-crowded with clumps of spawn, tadpoles or adult frogs.

However, as long as you have not introduced them from elsewhere, this is a perfectly normal situation. Amphibians can experience huge fluctuations in numbers and by laying large amounts of eggs they ensure that some of their offspring will survive the many perils they face in the first few weeks of life. Frogs are very important as natural prey for mammals, birds, reptiles, fish and aquatic invertebrates, and their numbers can also be limited by extremes of water temperature and disease. Your fish, newts and garden birds will find the spawn an excellent source of food. Moving adults and spawn away in one year is unlikely to reduce the number of frogs significantly as numbers will quickly build up in subsequent seasons to replace those removed. There may also be a risk of spreading disease and parasites.

By taking spawn or adults to another pond, you may increase the risk of spreading unwanted predatory fish or invasive plants. There is also the danger that you may be introducing animals to an unsuitable area. They are best left to their own devices in your garden where natural processes will regulate their numbers. It is early days yet, and there is still the risk of a heavy frost, which in itself will ‘kill off’ some of the spawn.