Of the three species of amphibian found in Ireland the common frog is by far the most familiar. Most people think of frogs as aquatic creatures, but in fact they spend most of their lives on land, only returning to the water in order to breed.
Adult frogs are from 6-10cm (2.4-4 inches) long. They are smooth skinned, tailless amphibians with powerful hind legs that are particularly well suited to jumping. The upper surface of the skin is variable in colour – ranging from a light yellowish brown to dark olive green. Some individuals even have a reddish tinge and almost black animals are not unheard of. Most animals exhibit a variable pattern of black or brown marks on the back and the species has a very distinctive brown patch behind each eye.
On the underside males tend to be a dirty white or pale yellow while females vary from pale yellow to orange. There are often brown speckles present in both sexes. Males tend to be slightly smaller than females and can be distinguished by the dark bluish-black nuptial pads – which are swellings on the first finger of their forelimbs. These swellings become much more pronounced during the breeding season and help the male to get a firm grip on the female’s smooth skin during mating.
Depending on the weather common frogs begin to emerge from hibernation in February or March and head straight for their freshwater breeding grounds. Males usually arrive before females and start croaking to attract a mate. Once females start to arrive the males start croaking in earnest and wrestle with each other to gain access to a potential mate. After overcoming his rivals a successful male will clamp himself to her back using his nuptial pads in a mating embrace known as “amplexus”. They may stay clamped together like this for days before spawning.
Eventually the female will lay 1000 to 4000 eggs which are fertilised by the male as they are released. This frog’s spawn floats in clumps protected by a jelly-like coating until the tadpoles emerge after 30-40 days. The tiny tadpoles feed on the remains of the frogspawn for the first two days before they switch to a diet of algae. As they grow bigger they also start to include aquatic insects in their diet. Hind legs develop at between six and nine weeks, the tadpoles lose their feathery gills and develop lungs – forcing them to the water’s surface to gulp air. Front legs are fully developed by about 11 weeks and the tail begins to be absorbed. At 12 weeks the metamorphosis is practically complete and the tiny froglet will leave the water, spending most of its time hiding in the vegetation on the water’s edge.
Frogs don’t feed during the breeding season, but once breeding is over they will eat practically any moving invertebrate that crosses their path, catching their prey with their long, sticky tongue. Adult frogs feed almost exclusively on land, but youngster frogs will also forage in the water. Although they are often seen by day frogs tend to be more active by night.
In winter frogs hibernate beneath compost heaps, under stones and logs or buried in the mud at the bottom of a pond where they survive by extracting oxygen from the water through their skin. They will not emerge until breeding time comes around again the following spring.
Photo Credit: All rights reserved by Foxglove Lane via the Ireland’s Wildlife Flickr Group