Amphibians are the only vertebrates to go through metamorphosis. This means that their young look different from their adult. Amphibians usually reproduce in early spring to late summer, though some reproduce in winter and fall. Most frogs and toads, such as the common frog ("Rana temporalis"), gather in large groups to ponds, rivers, swamps and lakes to breed. Male frogs and toads may croak to attract a female. When a female frog has chosen a mate, the male frog hops on top of her. They swim together as she lay eggs in the water. Sometimes, males fight to mate with a female. Frogs can lay up to 100 to 60,000 eggs in one clutch. This is called "frogspawn".