Results/Conclusions For both E. delphinii and A. stimulea, multiple measures of movement varied significantly among host plants. Host plant effects on both movement rate and the cumulative distance traveled by larvae of both caterpillar species were strongest 1 and 3 days after deploying the caterpillars and attenuated somewhat in subsequent censuses. In the early censuses, median movement rates and average movement distances tended to be enhanced on red oak and black cherry and reduced on white oak, with other hosts intermediate. Because of the highly skewed nature of the movement data set, we also examined site fidelity (the tendency to remain on the same leaf or leaf cluster between censuses) on the suite of host plants; for both caterpillar species, larvae had the greatest site fidelity on white oak and the lowest fidelity on black cherry, with other species intermediate. While the mechanism(s) promoting or inhibiting movement on these different hosts are currently not known, potential mechanisms as well as the potential consequences of increased movement for caterpillar growth and development and mortality from natural enemies are explored and discussed.