After an extensive 9–year survey of the Organization for Tropical Studies’ La Selva Biological Station (50-150 m elevation), the arthropods of La Selva (ALAS) project extended its sampling over a 2000m altitudinal transect on the slopes of Volcan Barva. Standardized samples have been taken at 300, 500, 1100, 1500 and 2000 m during the dry seasons of the past 5 years. In general, species richness declined with altitude. Small leaf-miners predominated in all samples, but even more so at higher elevations, and larger, non-leaf-miners were absent at the highest sample sites. Although sample sizes are small, middle and high elevation sites appeared to have faunas distinct from the lowlands and each other. At middle elevations the genus Neotrachys, whose hosts are ferns, was prominent. The majority of species sampled are undescribed.