Further details of tick distribution (Ixodes ricinus L.) on the pastures of a typical hill farm are given.

Sheep paths (tracks) and their borders have tick populations similar in density to that of the general pasture.

Sheep lairs (night resting places) have significantly lower nymphal densities than the general pasture. With males and females, though the difference is in the same direction, it is less well marked.

On the typical hill, the vegetation layer generally becomes thinner, and nymphal density decreases, with altitude. The case is not so clear with males and females. Provided vegetation conditions are suitable (i.e. sufficiently thick), altitude has no limiting effect on nymphal density distribution within the levels studied. Tick density distribution is therefore a function of vegetation conditions, the latter usually being affected by altitude.

Distribution of ticks on apparently uniform areas of vegetation is studied. Sampling methods are discussed. Probably no more than twelve nymphs per square yard of ground are present on the average in heavily infested pasture. The numbers of nymphs per 100 sq. yd. differed significantly. The number per acre (approx.) also differed significantly in rather more than half the cases observed. Larger areaunits within uniform stretches of pasture probably carry similar numbers of ticks.

Practical applications of the findings to the study of tick control are indicated.

Thanks are due to Dr V. B. Wigglesworth, F.R.S., Director, Agricultural Research Council Unit of Insect Physiology; Dr A. E. Cameron, Edinburgh University; and Captain the Hon. Claud Lambton, on whose farm the work was carried out.