A forest species of the northern Holarctic region, the type locality is Europe. It is known from up to 69°N in Norway and south to around 45°N in Europe and 35°N in the USA (Carpenter & La Casse, 1955; Stone et al., 1959). It often is regarded as a nuisance species, troublesome between June and August, biting man primarily around dusk (Marshall, 1938; Natvig, 1948; Covell & Shute, 1954; Vockeroth, 1954). Snow (1990) notes that they feed on mammals, including man, at dusk and during the night, and also in the daytime in shaded situations.

Experimental material
One female was trapped attacking man and the others were reared, in daylight, from larvae collected at Morden Bog, Dorset, England (50°41'N) on the evening of 24 July 1968 (sunrise 0516h and sunset 2056h BST, daylength 15h40m). The trapped female was used in experiments from 29 July, and reared adults were recorded from 9 August 1968, when they were 4-5 days post-emergence. Recordings were made with light-off at 2100h BST.

Experimental regimes
LD 6:18, one male, recorded for days two to five.
LD 8:16, one (captured) female, recorded for days three to six.
LD 12:12, one female, recorded for days two to four.
LD 18:6, two females, recorded for days two to six.

Results and discussion
The activity patterns are shown in Figure A13 below.
The results, although not very satisfactory, perhaps due to the low numbers of adults, show a bimodal E' and M'. Possibly this is a true crepuscular pattern, as E' is strong and diffuse in LD 18:6, and this fits the reported field pattern of dusk activity.

Figure A13

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