The aggregation of questing ticks, Rhipicephalus pulchellus, on grass stems, with observations on R.appendiculatus

Rhipicephalus pulchellus was observed to aggregate on the tips of grass stems in the field in Kenya. Laboratory studies of this behaviour, using simulated glass ‘stems’ in sand-trays, showed that this aggregation was not due to responses to either (a) chemical marks placed on the stems by climbing ticks, or (b) other stimuli transmitted down the stems by ticks already at their tips. Instead, the aggregation on stems appeared to be an adventitious result of the ticks aggregating on the ground (in the lab., under filter paper covering the sand substrate of the apparatus) and then climbing the nearest stem in due course. Briefer, comparative observations on R. appendiculatus indicated that it was much more mobile on the stems, spending less time at their tips, and not obviously aggregating.