Seasonal and Diurnal Activity of Harvestmen (Phalangida) and Spiders (Araneida) in Contrasted Habitats

In a previous paper on the balance of activity by day and night on the floor of two contrasted habitats (Williams 1959b), it was shown that an area of open scrub, Mill Copse, supported a smaller number of carnivorous ground beetles than an area of woodland, Rushy Mead. This was explained, in part, by the fact that the scrub is a poorer habitat and supports a less rich fauna, but it was also suggested that the difference may be related to the associated distribution of wolf spiders which are abundant in Mill Copse but sparse in Rushy Mead. The ecological equivalence of wolf spiders and ground beetles has not been tested in any way but was proposed as the animals are of equivalent size and share some habits as both groups are cursorial carnivores. The activity of the Lycosidae is examined in this paper and as inclusion of the remaining spiders and of the harvestmen would virtually complete the analysis of the cursorial carnivores these have been considered as well. This particular ecological category is the one best sampled by pitfalls as the animals are moving with sufficient momentum to fall readily into a trap and a fairly representative catch is possible. It is logical, therefore, that completion of this group should be the first aim of the analysis of ground activity. The methods of investigation have already been described (Williams 1959a) and are based on the use of pitfalls and on counts of animals moving in quadrats. The three areas investigated were Rushy Mead, Mill Copse and Mill Field, a newly seeded ley. Each area was sampled at 4-weekly intervals throughout the year by three pitfalls 1 m in circumference, and for a further year the first two were sampled approximately once a fortnight using a time-sorting pitfall in each (Williams 1958), the two traps operating simultaneously.