Nymphalidae is the largest family of butterflies with about 6,000 species distributed throughout most of the world. These are usually medium-sized to large butterflies. Most species have a reduced pair of forelegs and many hold their colourful wings flat when resting. They are also called brush-footed butterflies or four-footed butterflies, because they are known to stand on only four legs while the other two are curled up; in some species these forelegs have a brush-like set of hairs which gives this species its other common name. Many species are brightly coloured and include popular species such as the emperors, Monarch butterfly, admirals, tortoiseshells, and fritillaries. However, the underwings are, in contrast, often dull and in some species look remarkably like dead leaves, or are much paler, producing a cryptic effect that helps the butterflies disappear into their surroundings.