Vertical distribution, aggregation behavior, and longevity of larvae ofBoophilus microplus(Canestrini) were studied in hollow nylon mesh cylinders (85.1 by 2.54 cm), in smaller tubes (8 by 2.5 cm) at 0, 15.24, and 66 cm, and on guineagrass (Panicum maximumJacq.) plants in open shadehouses in Puerto Rico. The maximum period of larval longevity from egg eclosion to death at 0, 15.24 cm, 66 cm, free in cylinders, and free on plants was 58, 85, 90, 78, and 130 d, respectively. Vertical distribution of larvae free in cylinders ranged from 0 to 85.1 cm, with most observed in small aggregations between 15 and 85.1 cm. Before larval death, the number of aggregations and the number of larvae in each aggregation declined from a mean of 8 and 75 to 1 with 12 larvae.