They can, and it tends to happen around late summer. Wasps are at their most aggressive in August and September because the workers are focused on meat and sugars ahead of the winter.
Yellowjackets are not interested in crashing cookouts in June in the same way they are in August or September. Their behavior changes over the course of the season, and there is a biological reason for this.
Through spring and early summer, colonies raise larvae, and in order to do that, workers need to hunt insects to feed them. In exchange, the larvae produce a sugary secretion which the adults can consume. Late in the season, the queen stops laying eggs. The larvae are then mature and the sugar supply disappears. Thousands of adult workers are then left in great need of carbs with nothing to produce them at home. So they crash your cookout.
It’s not your imagination that the same insects that ignored you in June are ready to swarm you in September. They want the ham and lemonade, and they’re not even afraid to climb right into open soda cans. It’s also why they’re bolder and quicker to sting. Crowded colonies with declining resources get defensive quickly.
In Central New Jersey, this is usually a problem from early August all the way to the first hard frost. To deal with this, keep drinks in cups with lids or covered glasses rather than open cans. Be sure to serve food covered and clear plates promptly. Wipe up spills as they happen. Then keep trash and recycling in lidded containers away from the seating area. Traps can work if you place them at the edge of the yard away from where you sit. But if you put them too close, it might accidentally draw more to you.
If yellowjackets have taken over your patio, Mosquito Squad of Central New Jersey can help. Mosquito Squad locates and removes stinging insect nests and treats the spots where they build. This will help you protect your patio through the end of the season.
