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Ectatomma ruidum is a common ground-dwelling ant species in the Neotropics which has been reported as a potential biocontrol agent in maize and coffee-cocoa agroecosystems in Mexico and Nicaragua. Its spatial distribution and food preferences were evaluated between February and May 2007, both in shaded (with tree cover) and sunny (open) cattle pastures in the Pescador and El Palmar regions of southwestern Colombia. Two sunny and two shaded cattle pasture plots were selected at each region. Twenty consecutive, equilateral 25 m2 parcels were established at each plot. Nest locations were found by following trails from 20 equidistant tuna baits per parcel. The procedure was repeated during the wet and dry seasons with a total of 16 plot records. For determining food preferences, a paper disk providing five live ticks, five honey droplets and five Passiflora ligularis seeds was placed 30 cm away from the nest entrance, at one nest for each of 15 parcels per plot. Nest distribution was aggregated in shaded pastures, with an average nest density of 568 nests/ha, whereas it was mainly random in sunny pastures, with an average nest density of 1945 nests/ha. Whatever the season, E. ruidum nested preferentially in open places in both regions, apparently avoiding soil surfaces under the tree canopy cover in shaded pastures. This could explain the aggregated pattern recorded in these pastures despite some intraspecific competition. Foragers demonstrated a high capacity as seed dispersers, the myrmecochoric P. ligularis seeds representing 74.7% of the total weight of all food items removed. Comparatively, they were significantly less attracted by honey and ticks which were retrieved in similar quantities (14.3% and 11.0% of the total weight removed, respectively). In the course of this study, individual workers were observed carrying in their mandibles wild, natural ticks, captured in the field. This is the first report of ants naturally preying on ticks in Colombia. Our data confirm the status of E. ruidum as an important natural biocontrol agent which could be properly managed for ecological services in Neotropical agroecosystems. Inglés

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