When the weather reaches its hottest temperatures during the summer, and particularly in late summer, you may have noticed more bothersome and aggressive yellow jackets ruining your time spent outside. At this time of year yellowjackets seem to become more aggressive toward humans and animals. There is a reason for their increased obnoxiousness during this time of year, as this is when their normal social structure begins to collapse and change in tune with the growth of a colony’s population and the beginning of the next phase in their life cycle. This is a period of upheaval for these insects, and it causes a noticeable personality change.

The most common explanation given for this change in personality during the hotter months is that it is due to a change in their diet. During these late summer months yellow jacket populations within their colonies reach their peak, with one colony containing anywhere from 1,000 to 4,000 workers. Once it’s at this level, the hatching of new larvae slows down, leaving them with less larvae to provide food for. The common thought is that they begin foraging for more sugary, carbohydrate-filled nutrients instead just protein from insects. However, this has been rejected by certain yellowjacket experts, as they claim yellowjackets forage for both protein and sugary carbohydrates throughout the season.

The peak of the colony’s population and waning of new larvae does have something to do with their mood change, however. This also signifies the next step in the yellowjacket life cycle, during which the young yellowjackets begin to break off to form their own colony as the old one slowly dies. As the current queen grows older and approaches the end of her life, she produces the queens and reproductive males that will be needed to build a new colony as the current generation of workers die out. So, just as a colony’s population reaches its peak, its older workers start to die off. Social problems form as the current queen’s influence gradually wanes as she grows closer to death. This creates conflicts amongst the population as allegiances change from the old queen to a new one. While older workers die, some of the younger workers develop into the new queens and male reproductives that will eventually leave the nest and form a new one. Hormones start going wild, and some of these workers/new reproductives then start demanding regurgitated food from the poor leftover larvae, even killing them in the process of taking that nutrients. Their society is literally collapsing, causing these insects to lose control mentally, which understandably make yellowjackets a bit moodier and aggressive. If human society devolved into this kind of anarchy and tumult every year, you can probably imagine how crazy you would start to feel.

Do you notice a change in yellowjackets’ personalities and increased aggressiveness around late summer?