Eight surface-living insect species, two gyrinid beetles and six heteropteran bugs, were studied in 27 pools in a Tenerifestream. Gyrinus urinator was on average the most abundant species whereas Velia lindbergi was the most widely distributed one. Gyrinid abundance (numbers per pool), but not density (numbers per square metre), was positively associated with pool size and depth. In contrast, the densities of the bugs Velia lindbergi and Hydrometra stagnorum decreased with pool size. Both the number of species and individuals increased with pool area. Widely distributed species were represented with higher average densities than species with a more restricted distribution. Contrary to theory, there was a positive relationship between mean adult body size and density within the guild.
