DNAinfo did the dirty work of asking experts on the topic — New York's exterminators — why cockroaches take to the skies in summer. Subways, it seems, are a favorite flight path. "In hot steam tunnels, something with the temperature and the humidity encourages them to fly," Ken Schumann, an entomologist at Bell Environmental Services, told DNAinfo. "When it's warm and steamy that seems to be what they like." Great.