WOOD-LOUSE, a name commonly applied to certain terrestrial Isopoda (Crustacea) (q.v.), found in damp places, under stones or dead leaves, or among de caying wood. They form the tribe Oniscoi dea and are distinguished from all other Isopoda by living on land and breathing air, and by the small size of the anten nules and the absence of the mandibular palp. The head bears a pair of sessile corn pound eyes as well as the minute anten nules and the longer antennae. Each of the seven thoracic segments carries a pair of walking legs. The appendages of the abdomen (except the last pair) are flat membranous plates and serve as organs of respiration. In many cases their outer branches have small cavities opening to the out side by slit-like apertures, and giving rise internally to a system of ramifying tubules filled with air somewhat similar to the air tubes or tracheae of insects and other air-breathing Arthropods.
The female wood-louse carries her eggs, after they are extruded from the body, in a pouch or "marsupium" which covers the under surface of the thorax and is formed by overlapping plates attached to the bases of the first five pairs of legs. The young on leaving this pouch are like miniature aaults except that they are without the last pair of legs. Some twenty-four species of wood-lice occur in the British Islands. Some, like the common slaty-blue Porcellio scaber, are practically cosmopolitan. (W. T. C.) WOODPECKER, the name applied to certain birds, form ing together with the wrynecks (q.v.) the family Picidae, whose nearest allies are the toucans (q.v.). They generally have a bright particoloured plumage; the feet have two toes behind and two in front and the tail-quills are usually stiffened to form a prop on which the bird partially supports itself when climbing the trunks of trees.
The commonest species in Britain is the green woodpecker or yaffle (from its laughing cry), Picus viridis. It is about the size of a jay; the plumage is green, with a red crown and yellow rump. It obtains its food, con sisting mainly of grubs, from the bark and rotten wood of trees; in search of these, it mounts trees in a spiral direction and bores holes in the decaying portions with its chisel-like beak. It also feeds much on the ground, being espe cially fond of ants. The nest con sists of a hole drilled in the trunk of a tree, continued as a horizon tal passage that reaches the core, whence it runs downwards for nearly a foot to expand into a chamber in which about six white eggs are laid on a bedding of chips. The two other British species, the greater and lesser spotted woodpeckers (Dryobates major and D. minor) are similar
in habits, but have a plumage of black and white. They share with the red-headed woodpecker (Melanerpes erythrocephalus) of America, and other species, the habit of drumming with the beak on dead branches, etc., in lieu of a love-song. Inhabiting the pine forests of the Old World is the great black woodpecker (P. mar tius), larger than any of the previous species and with a black plumage and red crest. It is replaced in North America by the pileated woodpecker or log-cock, Ceophloeus pileatus, which is variegated with white.
The Californian woodpecker, Melanerpes formicivorus, displays an amount of providence beyond almost any other bird in the number of acorns it fixes tightly in holes which it makes in the bark of trees, and thus a large pine forty or fifty feet high will present the appearance of being closely studded with brass nails, the heads only being visible. This is not done to furnish food in winter, for the species migrates, and only returns in spring to the forests where its supplies are laid up. The acorns thus stored are always those which contain a maggot, and, being fitted into the sockets prepared for them cup-end foremost, the enclosed insects are unable to escape, as they otherwise would, and are thus ready for consumption by the birds on their return from their winter migration to the south.
All woodpeckers are fond of ants, but one form, Colaptes aura tus, the golden-winged woodpecker or flicker of North America, lives largely on grasshoppers and other ground insects and in this connection exhibits several interesting modifications, the bill being less sharp. The red is, in this species, reduced to a crescent on the neck. The red-shafted flicker (C. cafer) is a closely related spe cies; the two interbreed where their ranges overlap, producing a variety of segregating types. Other common North American forms are the hairy woodpecker (Dryobates villosus) and the smaller downy woodpecker (D. pubescens), both black and white forms. The North American sapsuckers (q.v.) are also wood peckers. Nearly one-half of the known species of woodpeckers occur in the New World. The remainder inhabit all parts of the Old World except Madagascar and the Australian region east of Celebes and Flores.
Some other woodpeckers deserve especial notice—the Colaptes or Soroplex campestris, which inhabits the treeless plains of Para guay and La Plata ; also the South-African woodpecker Geocolap tes olivaceus, which lives almost entirely on the ground or rocks, and picks a hole for its nest in the bank of a stream.