 Many Polistes species aggregate over winter . Polistes exclamans clump in rather large aggregations while hibernating . “ These aggregations are frequently found in protected places called hibernacula that can be as varied as crevices and cracks of rocks or trunks , beneath the bark of trees , between walls of buildings , or any other natural or artificial structures that provides protection during hibernation . ” Although Polistes exclamans have been found in organ @-@ pipe muddauber nests , a mud nest that can provide a certain level of protection , it is not thought to actually house hibernating Polistes exclamans over the winter . 
