In territorial Odonata, adult 6 3 may use 2 mating tactics that may be genetically or environmentally determined: territoriality and non-territoriality. The non-territorial tactic has been sometimes found to include 2 additional males: sneaking and wandering. The non-territorial 6 3, however, often have lower reproductive success than territorial 3 3. Studies on various Calopteryx spp. have repeatedly shown that territorial and non-territorial behaviours are conditional mating tactics and that body size does not predict 3 resource-holding potential and territorial behaviour. Instead, the resource holding potential seems to depend on the amount of 3 fat resources. Here, both territorial and wandering C. virgo 3 3 were collected from a creek in central Finland. It was found that territorial 3 3 were larger and heavier than wandering 3 3. The data show that the size of the individual may predict the reproductive tactic of some odon. 3 3 to a greater degree than previously thought.