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By using pitfall traps, the effects of rainfall and habitat type on the denso-activity of epigean arthropods Tenebrionidae in particular-inhabiting at Llanos de Challe National Park were investigated. This park is located in the Chile’s transitional coastal desert, Atacama’s III Region. Sampling was conducted during three days per month (september. october and december) in the period of maximal biological activity of the system, and in 1989 (dry no-ENSO year), 1997 (intense ENSO-year), and 2000 (damp no-ENSO year). Two pedological contrasting sites were used to compare the effects of the factors being examined: a coastal dune habitat and an interior stony habitat. The presence of 15 orders of Arthropoda was recorded. Hexapods made the > 95 % of total specimens captured (9,065 individuals), with Collembola (36.1 %) and Coleoptera (29.8 %) being the orders with the highest numerical representativeness. The numbers of orders with active members varied slightly among years: 13 orders were recorded in 1989 (44 % rainfall below the average), 15 in 1997 (443 % rainfall above the average), and 11 in 2000 (52 % above average). The effect of the ENSO event was clearly reflected in the numerical contribution both for the years Studied and for most of the recorded taxa. Although more Subtlety. this effect was also reflected in the assemblage composition of dominant taxa and between pedological habitats, particularly in regard to Tenebrionidae and Formicidae. Specially in the coastal dunes, Tenebrionidae clearly dominated the assemblage of epigean arthropods, being Gyriosomus Guerin-Meneville the most abundant and diverse genus. The dominance of Gyriosomus sets a number of questions regarding the levels of endemism, species diversity and distribution, and their functional role in the ecosystem Studied.