Orchesia undulata Kraatz, 1853

This is the most common and widespread of the European species of the genus; it occurs across most of Europe with the exception of the northernmost parts of Fennoscandia, Portugal, southern parts of the Balkans and Greece, it is absent from north western parts of Russia but may be spreading as it was only recently discovered in Lithuania and Macedonia, it is also known from north west Africa and extends east into parts of southern Russia. Here it is common throughout England and Wales, although the only island records seem to be from the Isle of Wight, and sporadic and rare in Scotland and the north of Ireland. Typical habitats include deciduous woodland and wooded parkland and pasture etc. and adults might occur on larger trees in hedgerows or on isolated large trees on waste-ground or in gardens, they are often associated with oak (Quercus L.) but may occur on a wide variety of trees and fallen timber in various stages of decay e.g. we swept them from foliage on coppiced hornbeams at Bricket Wood, South Hertfordshire on several occasions. Adults occur year-round, they overwinter among bark or decaying wood and are active from late spring until the autumn with numbers peaking in late summer; they are nocturnal and generally occur as individuals or in small numbers but swarms occasionally occur around fallen timber on the warmest evenings in the summer. Larvae develop through the spring and summer in decaying wood; in the UK they are often associated with the fungus Exidia glandulosa (Bull.) Fr. (1822) (Auriculariaceae) (a black, jelly-like wood-rotting fungus that typically occurs on oak), but in Europe they have been found in wood infested with Phlebia radiata Fr. (1821) and Merulius tremellosus Schrad. (1794) (both in Meruliaceae and both occur on a range of deciduous trees). Adults are occasionally active in warm weather and may visit hawthorn blossom, umbels or bramble flowers and they will occasionally appear in extractions of fungal material taken from wood but generally they will need to be looked for at night; searching low down on trunks, especially where there are areas of decaying wood, is a good way to find them as they are usually very obvious in torchlight, but catching them can be frustrating as they can move very rapidly and have a habit of jumping to escape danger when alarmed (which gives rise to the quaint common name of ‘mushroom jumpers’ used in Denmark), and once they fall out of sight they tend to be impossible to find, conversely for recording purposes they are distinctive enough to be readily identified in the field. Adults are fully winged and capable of flight but it seems they rarely do so.