In Southern Florida the immature stages of the mosquitoes Wyeomyia vanduzeei Dyar and Knab and Wy. medioalbipes Lutz are found in water held in the leaf axils of bromeliads. As part of a study of the factors controlling mosquito population size we have examined the relationship between the size of bromeliads and the numbers of the immature stages of mosquitoes inhabiting them. Larger plants contain more mosquitoes, but the relationship differs in the different development stages of the insects and suggests density-dependent control of the numbers and rates of development of larvae.