Although there is some detailed research on anaphylactic reactions to Hymenoptera venom, there continues to be little epidemiological data about the distribution, trend, and factors associated with the occurrence of Hymenoptera envenomations in humans. We describe characteristics of persons suffering Hymenoptera stings from bees, wasps, and hornets as reported to the Illinois Poison Center, and assess seasonal, climatologic, and time trends of calls for envenomations between 2002 and 2007. Mean daily temperature and mean daily atmospheric pressure were positively associated with envenomations, whereas wind speed was negatively associated with envenomations. We also observed a significant increase in calls for envenomations on summer holidays (P < 0.001). In addition, our findings showed that the number of calls for envenomations declined by nearly half after 2005 (P < 0.001) compared with previous years. Our findings indicate that the decline in bees, wasps, and hornets may be widespread, affecting both wild and commercial populations, and that the decline appears to have been rapid and sustained in recent years. Poison center data are a valuable resource for the surveillance of poisoning in humans, but our findings show that the data can be used to monitor changes in nonhuman species.