Every been bitten by yellow jackets when mowing the lawn? Their nest are usually in the ground. When you mow over the nest, start running, they’ll chase you down.
In late summer, foraging worker bees will pursue other food sources from meats to ripe fruits, or scavenge human garbage, sodas, picnics, etc., since larvae in the nest fail to meet requirements as a source of sugar.
http://en.wikipedia.org/wiki/Yellow_jacket#Nest