A single application of granular carbaryl approaching the lowest recommended rate to the shrub layer of a forested area in late spring significantly reduced the abundance of Ixodes scapularis Say nymphs throughout their peak activity period, but had little effect on Amblyomma americanum L. nymphs. Factors influencing the efficacy of the application are discussed. The possible explanations for the lack of efficacy of granular carbaryl against A. americanum, including behavior, formulation, and application rate, are discussed.