DAY VS. NIGHT SAMPLING FOR SPIDERS IN GRAPE VINEYARDS

We compared day sampling (between 0700 and 1100) and night sampling (between 1900 and 2300) of spiders on grapevines in a California vineyard in 1993 and 1994, shaking spiders from the vines onto a drop cloth and vacuuming them up. Pooled density of the seven most abundant spider species did not differ significantly between day and night sampling, nor did density of Cheiracanthium inclusum (Miturgidae), Trachelas pacificus (Corrinidae), Oxyopes spp. (Oxyopidae) or Neoscona oaxacensis (Araneidae). Under day sampling Metaphidippus vitis (Salticidae) was 60% more abundant and Hololena nedra (Agelenidae) more than 2.5 fold more abundant than under night sampling. Daytime sampling generally resulted in a higher percentage of capture for each spider taxa analyzed, but neither of the diversity indices (Shannon-Wiener, Simpson or Bray-Curtis) showed any difference between day and night sampling. Parameters generated by Taylor's power law indicate a uniform distribution for most spider taxa, which was not affected by sampling time with the exception of H. nedra. We suggest that at vineyard sites in California with a similar spider community, sampling can be limited to daylight hours if a sampling method is used which is sufficiently vigorous to dislodge spiders from their resting places.