Effect of Formica aserva Forel (Hymenoptera: Formicidae) on ground dwelling arthropods in central British Columbia.

Carabids and spiders have potential as bioindicators, but may experience niche overlap with some ants. While some studies have uncovered mixed responses by these taxa to ants, negative associations are frequently found. We examined carabids and spiders in a British Columbia clearcut in zones colonized and non-colonized by Formica aserva ants. The number of carabids captured in colonized and non-colonized zones differed significantly from expected, and species-specific patterns were observed. While the activity-abundance of most spider species did not differ between zones, the activity-abundances of five species were significantly different in colonized and non-colonized zones. We also investigated behavioural responses by the carabid Pterostichus adstrictus to signals of ant presence, and observed that this carabid avoided crushed F. aserva gasters. Our results indicate that F. aserva may influence the activity-abundance of some carabid and spider species, and that some carabids may be able to detect F. aserva chemical signals. -P. ii.