Frogs

Frogs are amphibians and are characterized by long hind legs, a short body, webbed toes, protruding eyes, but strangely for amphibians, no tail.  Unlike Toads they have a smooth skin and move about by jumping or climbing.  Male frogs make a low pitched call during the breeding season whereas toads make a louder higher croak.

Frogs ‘breath’ through their skin, especially under water, but use their lungs on land.  This is because the skin of a frog is permeable to oxygen, carbon dioxide and water.  Oxygen passes through the skin, by dissolving on an aqueous film on the skin, which then passes through to the blood stream.  For this reason the skin must remain moist at all times but is also why frogs are susceptible to toxins in the environment. Adult frogs feed on insects, slugs, snails and worms which they catch with a long sticky tongue and is why they are one of the ‘good guys’ in the garden.

There are only two species which are thought to be native to Britain, the Common Frog and the Pool Frog. It is however feared that the Pool frog has become extinct, as it was last seen in 1994, attempts are being made to re-introduce it in certain areas.  Some alien frog species live in Britain but are only found locally. These include Marsh frogs, edible frogs, and, confusingly, populations of pool frogs that are genetically distinct from the native form.

Frog Types

Common Frog (Rana temporaria)

These frogs are usually between 7.5-8 cm long but can be anywhere from 6-10cm in length.  They weigh approximately 22-23 grams and females are bigger than the males. This frog’s smooth skin varies in colour from grey, olive green, or yellow to various shades of brown with irregular dark blotches.  As well as being slightly smaller the males are darker and have a dark bluish-black swelling on the first finger.  This species of frog has dark shading round its’ eyes and ears which gives the appearance of a ‘mask’, dark bars on its legs and its’ underbelly is usually white or yellow sometimes with orange or brown speckles.

Common frogs also have the ability to lighten and darken their appearance to blend in with their environment. The eyes are usually brown with black horizontal pupils and transparent inner eyelids to protect their eyes whilst under water.  It is possible to find red or black frogs in Scotland and you may also find an albino common frog which has yellow skin and red eyes.  This is where it has been born without any pigmentation and without the usual camouflage it is even more vulnerable to predators.

The Common frog predominantly lives on land when not in the breeding season, it can be found in meadows, gardens and woodlands throughout the UK.  It prefers to breed in the shallow waters of puddles, ponds, lakes and canals and will not feed at all during this time.  Common Frogs are generally active all day but more so at night and are thought to live up to 8 years. 

Life Cycle

There are 4 stages in the life cycle of a Frog :

SPAWN – Thousands of eggs or ‘Frogspawn’ are laid in clumps in the still shallow waters of puddles, ponds, canals or lakes.  The eggs are very vulnerable and susceptible to predators, such as fish, birds and grass snakes. Usually eggs will hatch after 30-40 days.

TADPOLES – The eggs hatch into tadpoles which remain in the water for 5 weeks.  Frog tadpoles are mottled brownish-grey to olive with gold speckles, they have gills for respiration and a tail with fins for swimming.  Tadpoles feed at first on their surrounding jelly and then on the algae in the water.  Again they are very susceptible to predators and on average only 5 out of every 2000 will survive to adulthood.

METAMORPHOSIS – At the end of the tadpole stage frogs undergo metamorphosis where they make the transition from the tadpole to the adult frog.  This process takes 12-14 weeks during which the tadpole will grow front and hind legs, looses its’ gills and develops lungs.  Its’ intestines also change to allow it to move to a carnivorous diet and the eyes also begin to protrude and move to the side to allow for binocular vision. The final stage is when the frog looses its’ tail which is re-absorbed into its’ body.

ADULT – Around June/July the froglet is now ready to leave the water and feed on land.  It will continue to grow until it doubles in size and reaches maturity usually at 3 years when it will begin breeding itself.

Benefits

Frogs are most definitely the gardeners’ friend as they feast on insects, slugs and snails.  They are also an ideal introduction to wildlife for children.

Avoiding Dangers

Common frogs can sometimes die of 'ranavirus' or ‘red leg’, a disease which causes a variety of symptoms including lethargy, disorientation and ulcerations. It can also cause their legs to turn red. There is no evidence however to suggest that this disease affects people, pets or other pond life. To help reduce the risk of the disease spreading from one pond to another it is best not transfer spawn or adults between ponds.

Other things blamed for the reduction in frog numbers are shrinking habitat due to drainage schemes and industrial farming methods, increases in UV light intensity, heavy metal and chemical pollution, and acid rain. As with most wildlife, they are protected by the Wildlife and Countryside Act 1981 against exploitation for sale.

Encouraging Frogs

Avoid Slug Pellets

The use of slug pellets in the garden can be quite harmful to frogs.  Slug pellets include copper to give them their characteristic blue colour designed to make them unattractive to birds. Frogs feast on half dead slugs, some with slug pellets attached, and end up with large quantities of copper in their livers which damages their immune system, makes them more susceptible to disease and allows them to fall victim to the ‘red leg’ virus.

Avoid Pea Netting

If possible avoid using pea netting close to the ground as frogs can get caught up in it.

Ponds

The addition of some kind of pond or water feature in a sunny spot with no overhanging trees, a good mix of aquatic plants and most importantly with shallow edges will attract frogs and provide an ideal breeding environment.

Nesting Material

To attract frogs to your garden, don’t be too tidy!  Leave some long grass, a few piles of leaves, rocks, logs or wood stacks around and dark, damp corners for them to live and shelter in.

Hibernation

During the winter frogs hibernate in compost heaps, under stones or logs and under water beneath mud and decaying leaves. A plastic ball on the surface of a freezing pond can keep a hole in the ice to allow harmful gases (caused by rotting leaves amongst other things) to escape. Frogs will generally emerge in February to March to begin breeding.

Interesting facts

Heket was an Egyptian goddess, sometimes represented as a frog and at others as a human with a frog's head. She was said to look over fertility and pregnancy.

Eighteenth century scientists Luigi Galvani and Alessandro Volta helped discover how to produce electricity artificially after they noticed twitching frogs' legs.

The earliest known ‘proto’ frog dates from the Triassic period and is approximately 250 million years old. True frogs were in existence as long ago as the early Jurassic period, predating the appearance of most of the major dinosaur groups.