From https://en.wikipedia.org/wiki/Dragonfly#Sex_ratios:
Sex ratios
The sex ratio of male to female dragonflies varies both temporally and spatially. Adult dragonflies have a high male-biased ratio at breeding habitats. The male-bias ratio has contributed partially to the females using different habitats to avoid male harassment.
As seen in Hine's emerald dragonfly (Somatochlora hineana), male populations use wetland habitats, while females use dry meadows and marginal breeding habitats, only migrating to the wetlands to lay their eggs or to find mating partners.
Unwanted mating is energetically costly for females because it affects the amount of time that they are able to spend foraging.