There are around 20,000 species world wide and 312 British species. Most adult geometrids are nocturnal and rest with their broad, triangular-shaped forewings spread flat - see below - on each side of the body. They have a thin body, and a rather weak flight. In some species the females are flightless having reduced or vestigial wings. This means they have to walk to lay or disperse their eggs. A positive aspect of this is that they are able to do so in temperatures too low for flying; sometimes even below freezing. The caterpillars have only 2 pairs of prolegs (see above), and their locomotion gives them the common names of inch worm, and looper, and many of them can mimic twigs when disturbed. They are often found in trees, and if knocked off will hang from a silk thread, then climb back up.
Above is an adult Common white wave. The adults fly from May - August, and are fairly common in birch and alder woods. They have a wingspan of 25 - 30 mm, and a front wing length of 15 - 17 mm. The wings are shiny white with 3 rows of dotted lines on the fore wings, and 2 rows on the hind wings.
The caterpillars eat birch, alder, sweet chestnut, sallows and a variety of shrubs. There are 2 generations a year, and it overwinters as a pupa.
The brimstone (above) is common throughout Europe. They are found in hardwood forests, hedgerows, gardens and scrubland. There can be 2 or 3 generations a year, but just one in northern Scotland.
The caterpillar resembles a twig, and has an extra pair of prolegs, though these are smaller than the other 2 pairs. Its foodplants are hawthorn, blackthorn, plum, rowan and apple. It can reach a length of 33 mm.
Pupation is in a silken cocoon on or near the ground.
Adults fly from April to August (June and July in northern Scotland), and have a wingspan of 32 - 40 mm, and a front wing length of 14 - 21 mm. The female is usually larger than the male.
Eggs are laid in spring and all summer. There are 2 generations a year.
The Silver-ground carpet (above) is common in the U. K. It is most often found in damp places with herbaceous vegetation, such as hedges, woodland edges, downland, gardens and heaths. It is common and abundant. The caterpillars feed on low-growing plants such as primrose and bedstraw. It overwinters as a caterpillar.
It pupates in a cocoon in the ground.
The adults fly from May to July. The wingspan is 24-28 mm, the front wing length is 14 - 17 mm, and the band of colour across the wings can vary in brightness.
The Northern spinach, above, at rest on and below showing the underside of the wing on the right. It is widespread throughout Europe, but less common in southern England. It is found in mountains, heaths, bogs and fens. In the U. K. there is one generation a year.
Egg are laid in August, but do not hatch out until the following April.
The caterpillar foodplant is bilberry, cowberry, grey sallow, goat willow and other willows. The caterpillar feeds at night, resting on the foodplant by day with its body rigid, so it is not easy to see. Body length is up to 26 mm.
It pupates towards the end of May in leaves of the foodplant which it has sewn together.
The adults fly from June - August. The wingspan is 28 - 31 mm and front wing length 13 - 18 mm, the female is smaller than the male. The adult colours vary from straw yellow to brown. It overwinters as an egg.
Above is the Lunar thorn, Selenia lunularia, it can be found in open woodland and scrub. It is widespread in Europe, with a local distribution in the U. K.
The caterpillar foodplants are ash, blackthorn, dog rose, wild plum, birch, elm, oak, etc. It feeds mainly at night, resting during the day, and is very difficult to spot. Caterpillar body length can be up to 38 mm long. It overwinters as a pupa in a flimsy silk cocoon just below ground.
Adult forewing length is 16 - 22 mm. The adults fly from May - June, and there is sometimes a second generation that flies from July to August in southern England.