Frogs and toads are cold-blooded vertebrates. The colour of frogs varies. Generally, frogs are brown, light brown or olive green. The underside of frogs is generally white, and at the tops of their legs they are often yellow.
The frog normally spawns in April but in Lapland not until June. Males wait for females in the spawning grounds in large groups, and they attract them by croaking. In frogspawn, there is a transparent jelly that surrounds the eggs and acts like a small greenhouse. The black core warms up during the daytime in the sun, and the blanket of jelly provides insulation and stops heat from escaping. A frog will lay 1,500-3,000 eggs at a time. The eggs develop into larvae, which are called tadpoles. Initially, the tadpoles have gills, but gradually they metamorphose so that they ultimately breathe using lungs. During metamorphosis, the frogs develop hind legs first.
The female frog is often larger than the male. Frogs are generally 5-9 cm long, seldom more. They spend the winter in hibernation in the mud at the bottom of ditches, lakes and bays. Some individuals also hibernate on dry land or in other drier places. Often on a good winter site you can find dozens, if not hundreds, of individuals. During hibernation, frogs move every now and then. Frogs are at their most active when it is dark. They are common across the whole of Finland, but they have become rarer in recent years due to the loss of wetlands. The European common frog is a protected species.