Although called the common frog, this species is now becoming much less common in Britain, especially in rural areas. The widespread use of insecticides, and the diminishing number of breeding ponds has greatly reduced their numbers.
The colour of these frogs can vary a lot (see photos above), but the majority are olive-green with black patches. In addition to this camouflage colouring they have eyes and nostrils on top of their heads. This allows them to see and breathe while keeping most of their body hidden underwater.
Many frogs find refuge in urban gardens, but here too there are threats to the frogs survival. Domestic cats pose a danger, and also eating slugs, which have been poisoned by slug pellets.
The breeding season runs from January through to April, although some frogs will continue spawning until late summer. The bloated frog in the photo above is ready to spawn - hence the appearance.
Each female lays up to 2000 eggs (called frogspawn) in water. Only about 1 in 1,000 will survive to become a mature adult. After three or four weeks, the eggs hatch into tadpoles, which look like little fish. They breathe oxygen from the water through a pair of gills located just behind the head. (http://www.uksafari.com/frogs.htm)