The descriptive text, below the map, is from the Cornish Red Data Book (2009). The map on this web page depicts the organisms distribution and shows the records made pre-2000 and those made since.
This species occurs on the trunks of trees which have a basic bark, especially Elm Ulmus spp. It has declined rapidly in recent years due to the demise of the Elm population caused by Dutch Elm disease. In England, Scotland and Wales as a whole, the species has declined from 218 to just 26 10km squares. In Britain this species is almost entirely confined to the bark of mature Elms and Sycamores Acer pseudoplatanus , usually in raintracks or below old wounds. It has been recorded on four Elm trees on St. Mary' s, Isles of Scilly (2002); numerous Sycamore trees on the Godolphin Estate, West Cornwall; and on a Field Maple Acer campestre in the grounds of Anthony House in south-east Cornwall and on wounded Horse Chestnut Aesculus hippocastanum at Lanhydrock. More recently (2007/8) it has been recorded on Ash Fraxinus excelsior and Sycamore at Penwarne near Mawnan Smith (SW7630) and on an Elm on the Trelissick Estate near Truro. Elsewhere in Britain it is sparingly known from Devon, Dorset, Somerset, S.Hampshire, Surrey, Sussex,
S.Wales, S.E. and N.E. Scotland, often on one or two trees only. Any sites where a viable population is known to persist, especially on trees other than Elm, should be afforded protection. Tree Preservation Orders should be placed on individual trees. In the case of the population on the Isles of Scilly there is the possibility of trying to extend the available habitat for the species by pollarding or cutting branches of the numerous nearby, mature Elms to create seepage tracks.
I.J. Bennallick, S. Board, C.N. French, P.A. Gainey, C. Neil, R. Parslow, A. Spalding and P.E. Tompsett. eds. 2009. Red Data Book for Cornwall and the Isles of Scilly. 2nd Edition.Croceago Press.
The Cornish Red Data Book Project was led by the Cornwall and Isles of Scilly Federation for Biological Recorders (CISFBR). The full text and species accounts (minus the maps) are available on the CISFBR website.