Distribution: This Holarctic species is widely distributed from Northern and Central Europe to Siberia and less frequent in the southern countries; in the Mediterranean region it seems to be replaced by Cs. litorea (Cranston et al. 1987, Schaffner et al. 2001).

Habitat: Aquatic stages are encountered in fresh or more rarely in slightly brackish waters, including pools, wells, backwaters, small ponds or ditches, overgrown with vegetation, and peat bogs; they mostly inhabit temporary waters, either open to the sun or heavily shaded and often rich in detritus (Mohrig 1969, Briegel 1973, Rettich et al. 1978, Cranston et al. 1987, Schaffner et al. 2001, Becker et al. 2003). Moreover Marshall (1938) notes a single record of larvae found in a tree hole, associated with Anopheles plumbeus and Ochlerotatus geniculatus.

Biology: The species is univoltine, eggs are laid individually in dry hollows littered with dead vegetation or on banks of drying pools; larvae hatch in autumn or in winter, when their breeding sites are flooded, and overwinter in the larval stage (Marshall 1938, Mohrig 1969, Schaffner et al. 2001). They are present from autumn throughout winter and spring. During the winter months larvae often descend to the bottom of the breeding site, where they lie in an inverted position with their head setae and tip of the siphon in contact with the ground; they are able to survive under coverage of ice, but entire freezing of the water body leads to a high mortality (Becker et al. 2003).

Adults: Adults emerge from the end of April until June and disappear in late summer or autumn (Service 1968a, Mohrig 1969, Schaffner et al. 2001).

Females seem to feed essentially on birds and are not aggressive to mammals and humans (Mohrig 1969, Schaffner et al. 2001, Becker et al. 2003); however Service (1968a) notes that they rarely may chose reptilian or mammalian blood, including that of man. Cs. morsitans may be infected by the Sindbis virus (Ockelbo); according to its trophic preferences the risk of parasitic transmission to humans is insignificant (Schaffner et al. 2001).