There have been a lot of reports of, and question about, large amounts of dragonflies that have been observed across the region. People have asked what could be the reason as it’s been fairly dry over the past month or so.
Dragonflies do prosper and procreate more rapidly in standing water. They also feed on mosquitoes and other insects that do well when there is a surplus of standing well. These two facts help dragonflies to have increases in population during wet years.
Why we are seeing large numbers now has more to do with not the recent weather but the fact that we had our wettest year on record last year and the wet weather continued into early this year. The image below shows the rainfall records for State College, of which 2019 was the wettest ever.
Other areas broke rainfall records, some by over 10 inches. This wet weather left plenty of areas for the dragonflies to lay their eggs and for their larvae to grow and hold through the winter. Therefore the local number of dragonflies have increased.
On top of the local insects, there are some dragonflies that migrate each year. They travel southward during the autumn and move northward during the spring. There have been numerous reports of these swarms in Ohio and Pennsylvania recently. In fact, the regional National Weather Service Doppler radars have picked up what most likely was swarms of dragonflies, albeit probably mixed in with birds feasting on them.