An aggregation of adults of the ashgray blister beetle, Epicauta fabricii (LeConte), was censused repeatedly for activity on the legume Baptisia australis (L.) in the tallgrass prairie of eastern Kansas. The aggregation persisted for three weeks. Males were more abundant than females throughout the period of aggregation, although females gradually increased in relative abundance over the three-week period. Overall, only 5% of observations were of mating; mating activity was greatest in the early stages of aggregation. The two sexes were similar in the frequency of feeding and in the kinds of plant tissue on which they fed. During the first two weeks of aggregation, the beetles fed primarily on reproductive tissues; in the last week of aggregation, they fed primarily on leaves and stems. The timing of beetle tenure on the host plant was well-suited for consuming the large crop of developing young fruits. Voracious feeding by blister beetles greatly reduced host plant reproductive success; only 20% of the buds, flowers, and fruits present when the aggregation was initiated escaped consumption by the beetles. The seasonal timing of aggregations results in early-opening flowers (and associated fruits and seeds) of the host plant having the greatest chance of escaping destruction by the blister beetles