Treefall gaps alter abiotic and biotic conditions in patches of the forest floor, which can have large effects on arthropod communities. We explored the importance of treefall gaps on arthropod communities using malaise traps and comparing 19 different arthropod groups and their abundance between gaps and neighboring understory sites during the rainy and dry season in Panama. We measured differences in several abiotic and biotic conditions that might influence arthropod abundance. We found that gaps have more light, higher temperatures, lower humidity, higher plant densities and more young leaves than in the understory. In the dry season, the abiotic conditions are the most stressful in gaps and young leaf densities are at the lowest. Many arthropod groups had an association with gap or understory habitats, either all year or during certain seasons. In general, there was a higher total abundance in gaps during the rainy season and understory during the dry season. Predator populations were correlated with herbivore populations in the rainy season, but not in the dry season. Therefore, in the rainy season, predator populations appear to track herbivore populations. However, in the dry season, predators are controlled by factors other than resources. We concluded that in the dry season, when abiotic conditions are the most stressful in gaps and there are little food resource incentives, arthropods avoid gaps. In the rainy season young leaf production and less intense abiotic conditions in gaps, create favorable conditions for arthropod growth and activity.