The ecology of the sheep tick, Ixodes ricinus L. The seasonal activity in Britain with particular reference to Northern England

Abstract

A survey of tick activity curve data for Britain shows:There are usually two peaks of female activity per annum, one peak in ‘spring’ and a lesser one in ‘autumn’, the date limits of the ‘seasons’ being slightly elastic. For a greater or lesser period in summer female-tick activity is low or practically absent, while in winter it is practically absent.There are exceptions to the biannual type of female activity. In three areas, only one annual peak occurs. At Hethpool, north-eastern Northumberland, and in Ettrick Valley, southern Scotland, this single peak is in April–May; in the Hill o'Fare area, north-eastern Scotland, it is in July.The theory of temperature control of activity (the limits being the range 45–60° F. average weekly maximum shade temperature, i.e. corresponding to spring and autumn conditions in Britain) does not stand up to the following facts: At Hethpool, following a spring female activity confined to the range 45–60° F., there was no autumn recrudescence when temperatures again passed through the same range. About half the annual female activity at Crag, south-western Cumberland, and practically all in the Hill o'Fare area occurred at temperatures of 60–70° F. and 60–65° F. respectively.Solar radiation, evaporativity and humidity, as well as temperatures, of the macro-climate were investigated in relation to female activity. The tentative conclusion is that the duration of humidity level during daylight, in conjunction with temperature, may partly decide the amount and extent of activity in summer.In spring, where spring activity obtains, males and females appear in small numbers a few weeks before nymphs. The bulk of male, female and nymphal spring activity, however, is concurrent, the curves having peaks at approximately the same date.Again, where spring activity obtains, spring larval activity commences later than that of males, females and nymphs, the peak being about 1 month later.Theories of seasonal activity are discussed.