Male-male tandem formation in odonates is typically described as a mistaken sexual advance by one male on another. If so, male-male tandem formation should be less frequent in more sexually dimorphic species. In a small experiment.designed to describepatterns of intra- and interspecific aggression by Micrathyria atra and M. mengeri, I placed live tethered male decoys of these species in the territories of territorial males. In the less sexually dimorphic M. mengeri, nine of 21 intraspecific interactions by three different males resulted in male-male tandem attempts. In the more sexually dimorphic M. atra, only one of 25 intraspecific interactions resulted in a male-male tandem attempt. The higher incidence of male-male tandem formation in M. mengeri may reflect a greater mistake rate by males in this less dimorphic species.
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