The ecology of the tick Ixodes trianguliceps Bir. is described from material collected at two localities in Wytham Estate near Oxford. The hosts examined were bank voles, Clethrionomys glareolus Schr., field voles, Microtus agrestis (L.), and field mice, Apodemus sylvaticus (L.).

The seasonal distribution of the tick is biannual, with spring and autumnal peaks as found in Ixodes ricinus (L.). Larvae occur throughout the year but principally in spring and autumn. Nymphs are found only from late spring until the autumn, and adults principally in the spring with a small peak in autumn.

Larvae and nymphs of I. trianguliceps were more abundant on male than on female bank voles, but there was no significant difference in the infestation of males and females by adult ticks. Similarly there was no significant difference in the infestation of adult and juvenile bank voles.

Larvae and nymphs occur principally on the ears, but the adult ticks are found mainly on the neck or body, although the ears were not excluded from infestation.

The seasonal distribution and life-history is discussed with reference to similar studies made in the Soviet Union and in Poland. Male ticks were found in copula on the host, and both males and nymphs were collected from the nests of voles.

A tentative summary of the life-history of I. trianguliceps is given based on known facts for the hedgehog tick, Ixodes hexagonus Leach, which has a similar seasonal occurrence.

We wish to thank Professor Don Arthur for identification of much of the tick material, especially in the early stages of this study, and for useful criticism of the draft manuscript. The work was carried out while one of us (M.J.C.) was a research student in the Hope Department of Entomology, Oxford, and the other (C.H.S.W.) a research student at the Bureau of Animal Population, Oxford. For facilities in both departments we wish to express our gratitude.