Strange Sightings

Last night around 7:00 p.m. we saw the strangest things in our yard. There were tons and tons of dragon flies being chased around by lots and lots and lots of barn swallows. All of the swooping around as barn swallows do; the dragon flies evidently trying to keep away from the birds. Good thing I didn't have to be outside! Do dragon flies migrate? Is that why there were so many?