Two genera of carabid beetles overwintering in a single air cell at Birlingham, Worcestershire

P.F. Whitehead.

Moor Leys, Little Comberton, Pershore, Worcestershire WR10 3EH Email: paul@thewhiteheads.eu

The overwintering by beetles of various families in terrestrial or arboreal air cells is reasonably well-known (Whitehead, 1992) especially in riparian situations. Amongst the genus Carabus in which it is frequently encountered, Carabus granulatus L., 1758 is noted for its ability to use soft rafted wood or suitable standing trees in which to cut and maintain air cells. The cells are usually somewhat larger than a single beetle and reinforced with a barrier of compressed chewed wood which creates a cell that helps resist the ingress of rising flood water and insulate the insects.

In two contributions the author has demonstrated that on occasion pairs of the same species may co-operate to construct and maintain a single cell. At Bialowieza National Park, Poland, on 27 September 1998 a pair of Carabus cancellatus Illiger, 1798 were found in an established air cell under the appressed bark of a long-fallen Norway Spruce Picea abies L. thus raising interesting questions regarding pair-bonding, division of labour, survival and reproductive success (Whitehead, 2001). During January 2006 at Slimbridge, Gloucestershire, three individual Carabus granulatus had co-operated to cut a single overwintering cell and were found together in it (Whitehead, 2006). The cell had a maximum depth of 31mm and a maximum breadth of 36mm and was situated beneath the trunk bark of a fallen Crack Willow Salix fragilis L. on the grazing levels of the estuarine River Severn.

A finding at Birlingham, Worcestershire (SO94 12 m a.s.l.) on 26 December 2014 is perhaps unique, for it involves the cooperation of two individuals of different genera of carabid beetles, namely Carabus granulatus and Pterostichus niger (Schaller, 1783), in creating and maintaining a single large air cell defined circumferentially by macerated wood fragments deep inside a soft flood-rafted willow trunk Salix sp. Although it remains unknown how the two insects cooperated in this case it seems that both recognised the mutually conferred benefits of their labours and were content to cohabit in this way.

References

Whitehead, P. F. 1992. The floodplain Coleoptera of the River Avon, Worcestershire, England, with provisional diagnoses of ancient assemblages. Elytron 6:15-33.

Whitehead, P. F. 2001. Pair-bonding in Carabus cancellatus Ill. (Col., Carabidae). Entomologist's monthly Magazine 137:114.

Whitehead, P. F. 2006. Evidence of social organisation in overwintering Carabus granulatus L., 1758 (Col., Carabidae). Entomologist's monthly Magazine 142:141.