In tropical rain forests, harvestmen assemblages are extremely diverse, with richness often exceeding 25 species. In the neotropics, there are published accounts of harvestmen faunas in South America rainforests (especially Amazonia), but relatively little is known about the community ecology of harvestmen in tropical forests of Central America. In this paper, we provide the first insights into the diverse assemblage of harvestmen inhabiting a wet forest at La Selva Biological Station, Costa Rica. Over five field seasons, we recorded 38 species. During our 2009 field season, we examined variation in species abundance, richness, and composition between adjacent successional forests (young secondary, mature secondary, and primary forests) as well as between distinct habitats (ground/litter layer and shrub/tree layer). Based on night samples (but not day), our results indicate that there are only minor differences in species composition and relative abundance between the forest ages, but no differences in richness. The ground/litter layer and shrub/tree layer habitats differed markedly in species composition, species richness, and relative abundance of several species. Our analysis of covariance supports the hypothesis that leg length is related to climbing behavior for several species belonging to Eupnoi and Laniatores. 1. Introduction The order Opiliones (harvestmen) represents the third most diverse group of arachnids after mites and ticks (Acari) and spiders (Araneae). With more than 6500 described species distributed across all major continents (except Antarctica), harvestmen have become a useful group for biologists interested in investigating biogeography [1, 2] and monitoring the impacts of habitat disturbance and forest fragmentation [3]. Due to their relatively high abundance and rich diversity in neotropical forests, harvestmen have been characterized as potentially useful candidates for a variety of ecological studies [4]. However, the majority of field studies of harvestmen have focused on single species or a small subset of an assemblage, providing little information of interactions at the community level (see review by Curtis and Machado [4]). The few studies that have examined the community ecology of harvestmen were primarily conducted in temperate forests [5–8]. Recently, diversity and habitat use of species within neotropical communities have been investigated in Brazil [3, 9, 10]. The most diverse harvestmen communities occur in neotropical rainforests, where richness may exceed 25 species [1, 9, 11]. The highest diversity at a single
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