There is a growing movement toward mosquito control that doesn't involve spraying organophosphates and synthetic pyrethroids, both of which can kill people when used incorrectly and can decimate beneficial insect populations, on top of failing to control mosquitoes in many cases.
Some sources recommend dragonflies as a natural mosquito control. Adult dragonflies do eat mosquitoes; however, there is good evidence that mosquitoes are not an important food for adult dragonflies. There is also good evidence that dragonfly nymphs can reduce mosquito populations in experimental settings. Let's dive into the data.
There are around 7000 species of dragonfly worldwide, and so far a few species have shown promise. A 2018 study found that Red Rockdwellers can actually reduce populations of container-breeding mosquitoes. Red Rockdwellers naturally lay their eggs in shallow rocky pools, so it wasn't hard to get them to lay eggs in artificial containers. The containers with Red Rockdweller nymphs had fewer mosquito larvae than the containers without them.
Figure 1: Image of a Red Rockdweller by Quercus19 on iNaturalist (https://www.inaturalist.org/observations/125061688)
One problem for those of us Stateside: this beautiful dragonfly is only found in central Africa.
Figure 2: Screenshot of Red Rockdweller observations from iNaturalist (https://www.inaturalist.org/observations?place_id=any&subview=map&taxon_id=96002.)
Well, what about dragonflies in the US? Almost no studies on dragonfly biocontrol have been conducted in the United States, according to a 2023 meta-analysis of dragonfly nymph predation on mosquitoes.
Figure 3: Map of studies that assessed dragonfly nymph predation rates on mosquitoes (https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2656.13965)
Why is so much of the research done in desert and tropical areas instead of temperate areas like North America? It may be that our dragonflies aren't up to the task of thriving in the artificial habitats mosquitoes love. When researchers tried to control mosquitoes with dragonflies in Maine, they had to constantly replace dead dragonfly nymphs that could not survive in the artificial containers. And even when they replaced the dead nymphs, the mosquito population remained unaffected. So what about gardening articles that recommend planting dragonfly gardens to control mosquitoes? They may be putting you at greater risk of mosquito bites and mosquito borne illnesses.
Selected Bibliography:
Acquah-Lamptey, D. and Brandl, R.: Effect of a dragonfly (Bradinopyga strachani Kirby, 1900) on the density of mosquito larvae in a field experiment using mesocosms, Web Ecol., 18, 81–89, https://doi.org/10.5194/we-18-81-2018, 2018.
Lee, J.M., Wasserman, R.J., Wilson, R.F. et al. Limited Effect of Ground Floor Fogging on Mosquito Distribution in High-Rise Condominia. EcoHealth20, 65–73 (2023). https://doi.org/10.1007/s10393-023-01629-8
Priyadarshana, T. S., & Slade, E. M. (2023). A meta-analysis reveals that dragonflies and damselflies can provide effective biological control of mosquitoes. Journal of Animal Ecology, 92, 1589–1600. https://doi.org/10.1111/1365-2656.13965