What month are yellow jackets most aggressive?

Yellow jackets are most aggressive in late summer, particularly in August and September, when colonies reach peak size and workers become more defensive and more attracted to human foods seeking sugars, though they are active from spring through fall. In spring, queens emerge from overwintering and start new nests, colonies are small and yellow jackets are less noticeable and less aggressive. By midsummer, colonies grow larger with hundreds to thousands of workers foraging for protein to feed larvae. By late summer, colonies reach maximum size, larvae that produce sugary secretion for workers mature and leave, so workers lose sugar source and start seeking sugars from human foods, fruits, sodas, and picnics, making them more nuisance and more likely to sting when competing for food or when swatted. In August and September, yellow jackets are also more defensive of nests and more active in warm weather, and they are attracted to overripe fruits and fermented substances, sometimes becoming intoxicated and more irritable. They are also more likely to sting when trapped in clothing or when nests are disturbed during yard work. So most aggressive months are August and September, with July also aggressive. To reduce aggression, keep food and sweet drinks covered outdoors, seal trash cans, avoid swatting, and remove nests professionally in early summer before they become large and aggressive.