The Phenology of Some Surface-Active Arthropods of Moorland Country in North Wales

Calluna vulgaris (L.) Hull, Erica cinerea L. and Vaccinium myrtillus L. among eroded peat and broken stones which were encrusted with the thalloid lichen Hypogymnia physodes (L.) Wats. and the fruticose lichen Cladonia impexa Harm. Site B was at 450 m on a vegetation of heavily grazed Festuca ovina agg. with extensive patches of Vaccinium and small patches of Calluna, Ulex europaeus (L.) and U. gallii Planch. Site C, at 360 m, was on heavily grazed grassland, a mixture of Festuca and Agrostis. During summer and autumn the area had a thin cover of Pteridium aquilinum (L.) Kuhn. Site D, at a height of 240 m, was in a field which was only occasionally grazed. The grasses, largely Agrostis gigantea Roth., and Deschampsia caespitosa (L.) Beauv., produced a thick mat 15-20 cm high. Scattered patches of dense bracken also occurred in the sampling area. This matted vegetation at site D provided a less exposed habitat than the vegetation at A, B and C. Movement of arthropods through the vegetation and over its surface was probably more difficult at D than elsewhere. Pitfall traps were used for the collection of the animals. The traps were honey jars with an internal diameter of 6 cm, and they were sunk into the ground so that their mouths were flush with the soil surface. Thirty of these were used at each site. They were laid out in three rows of ten and each jar was 5 m from adjacent jars. To reduce the carnivorous activities of the trapped animals 1000 glycerol in water was placed into the bottom of each pot. Each trap was replaced at weekly intervals and the contents were sorted in the