Biological studies on certain species of British phalangida

Abstract

From 1957 to 1960 both field, and laboratory studies were carried out on six British species of woodland harvest- spider, Lacinius ephippiatus (C. L, Koch), Mitopus morio (Fabr.), Nemastoma lugubre (Mull.), Odiellus palpinalis (Herbst), Oligolophus agrestis (Meade) and Oligolophus tridens (C. L. Koch.) The only comparable study is that of Todd (1949, Journal of Animal Ecology, 18, 209-89) whose findings were, in general, restricted to adult harvest- spiders: hence in the present study many of Todd's ideas, were extended to juveniles. Initially a method of determining the various life stages (instars), based on the femur length of the second walking leg, was found for each of the above species Using this information the course of seasonal development of each species was followed in detail: it was also found that, while all instars of L, ephippiatus, N. lugubre. O. palpinalis and O. tridens were exclusively ground dwelling in habit, an extension of range from the ground layer into the shrub layer and tree canopy occurred in the penultimate and final instars of M.. Morio. and O, agrestis. Most of the interstratal movement was restricted to the period between dusk and midnight. To find the cause of the vertical migration these findings were compared with the results of laboratory Studies on temperature and relative humidity preferenda, resistance to dessication and locomotor activity patterns, and with microclimate measurements made in the field. It became clear that, although very closely associated, seasonal migration should be considered separately from diel migration. The former was caused by endogenous factors probably associated with reproduction and not by any change in the physical conditions affecting the various instars. The latter was 'triggered' by the loss of light at dusk, but was not necessarily caused by the increase in the intensity of locomotor activity resulting from this loss.