These are one of the most dangerous stinging insects we have here in southern Ontario, Bald-face Hornets. They are a social insect that is very sensitive to vibration. Mowing your lawn, children playing or any quick movements near a nest could make them agitated and aggressive and quickly swarm what they think is a threat. They are protective of their nest and usually hang trees or on overhangs of buildings. They can be easily be distinguished from yellowjacket wasp by their colouring, white and black. They range in size from 3/4 of an inch to over an inch which can be intimidating when flying around you at a barbecue or park. We strongly recommend you call a licensed professional if you have any nests on your property.