The Double Square-spot (Xestia triangulum) is a moth

Moth

A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

 of the family Noctuidae

Noctuidae

The Noctuidae or owlet moths are a family of robustly-built moths that includes more than 35,000 known species out of possibly 100,000 total, in more than 4,200 genera. They constitute the largest family in the Lepidoptera....

. It is distributed through most of Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

.
This species has pale brown forewings marked with two distinctive black marks (despite the common name only one of these is square, the other being roughly triangular). The hindwings are similar in colour to the forewings. The wingspan

Wingspan

The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...

 is 36-46 mm. The moth flies at night in June and July and is attracted to light and sugar and to flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

s such as wood sage.

The larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

 is brown with black marks and is polyphagous, feeding on a wide variety of plants including birch

Birch

Birch is a tree or shrub of the genus Betula , in the family Betulaceae, closely related to the beech/oak family, Fagaceae. The Betula genus contains 30–60 known taxa...

, blackthorn

Blackthorn

Prunus spinosa is a species of Prunus native to Europe, western Asia, and locally in northwest Africa. It is also locally naturalised in New Zealand and eastern North America....

, bramble

Bramble

Brambles are thorny plants of the genus Rubus, in the rose family . Bramble fruit is the fruit of any such plant, including the blackberry and raspberry. The word comes from Germanic *bram-bezi, whence also German Brombeere , Dutch Braam and French framboise...

, dock

Rumex

The docks and sorrels, genus Rumex L., are a genus of about 200 species of annual, biennial and perennial herbs in the buckwheat family Polygonaceae....

, hawthorn

Crataegus

Crataegus , commonly called hawthorn or thornapple, is a large genus of shrubs and trees in the rose family, Rosaceae, native to temperate regions of the Northern Hemisphere in Europe, Asia and North America. The name hawthorn was originally applied to the species native to northern Europe,...

, raspberry

Raspberry

The raspberry or hindberry is the edible fruit of a multitude of plant species in the genus Rubus, most of which are in the subgenus Idaeobatus; the name also applies to these plants themselves...

 and sallow

Goat Willow

Salix caprea , is a common species of willow native to Europe and western and central Asia....

. The species overwinters as a larva.

1. The flight season refers to the British Isles
   British Isles
   The British Isles are a group of islands off the northwest coast of continental Europe that include the islands of Great Britain and Ireland and over six thousand smaller isles. There are two sovereign states located on the islands: the United Kingdom of Great Britain and Northern Ireland and...
   
   . This may vary in other parts of the range.