The Ferreira Penna Scientific Station (ECFP), with near 33.000 ha, is located at Caxiuanã National Forest, Pará state, Brazil. A structured protocol of ground litter spiders sampling resulted in 400 samples of 1m² concentrated litter, from both rainy and dry seasons. The spiders were sorted by a combination of manual sorting and Winkler device techniques. These samples were obtained in five plots, three located in Terra Firme (dryland) forest (LBA-EXP, LBA-CON and TF-IMC) and two in igapó (wetland) forest (IG-N and IG-S). One of the Terra Firme plots (LBA-EXP) is under hidric stress and it was used plastic panels and gutters to exclude most of the rainfall. A total of 2230 individuals (mean: 5,6 individuals / m²), beionging to 34 families, were collected. Seven families were represented only by juveniles: Nesticidae, Pisauridae, Gnaphosidae, Mimetidae, Deinopidae, Oxiopidae, Uloboridae. The most abundant families were Salticidae, Theridiidae, Ctenidae, Oonopidae and Linyphiidae. 876 adults, beionging to 120 species or morphospecies in 27 families were sampled. The most abundant species were Styposis sp.3 (Theridiidae), with 16,55% of all adults, Anapisona sp.1 (Anapidae), with 6,96%, Meioneta sp.1 (Linyphiidae), with 6,39%, Oonopidae sp.1, with 5,59% and Salticidae sp.1, with 4,56%. In order to implement the majority of the analysis, 15 occasional species were excluded. The observed species accumulation curves for all samples and for the samples from each plot didn't reach the asymptote in the end of samples addition. The patterns of abundance and incidence of these species suggest the existence of total species richness from 123 to 184 species. The largest species richness estimates were from plot LBA-EXP (75 - 110 species). The smallest ones were observed at plot IG-N (25 - 59 species). Despite the species richness and the abundance of spiders had reached the largest values at plot LBA-EXP, the overall diversity was larger at plots LBA-CON and TF-IMC. The Igapó overall diversity was lower than in Terra Firme. The species composition was different in Terra Firme and Igapó habitats, as demonstrated by similarity indexes and percentage complementarity. The abundance and species richness of litter spiders increased in dry period and decreased with the raising of soil residual humidity.
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