Herbivorous insects can be an important part of weed management, but it is necessary to understand the life history of the organisms involved and how they interact. This is especially pertinent when dealing with endophagous insects with restricted mobility. Hadroplontus litura F. is a stem-mining weevil that is considered a biological control agent of Canada thistle (Cirsium arvense L.), a perennial weed that forms clonal networks. We investigated the biology of H. litura and its association with Canada thistle at six field sites along a latitudinal gradient over 2 yrs, including documenting immature phenology and feeding damage, quantifying immature life stages, and exploring relationships between weevils and shoot size as well as weevil density and feeding damage. Eggs were present until the beginning of June and third-instar larvae began to exit shoots in mid-June, although some were present in July. It appeared that adult females laid more eggs on larger shoots, and preferred shoots not previously used for oviposition. The head capsule size of third instars was not correlated with shoot size, but it was positively related to larval density. Overall, infested shoots had an average of four weevil immatures, although densities ranged up to 21. Larval density was positively associated with stem damage, and both parameters appeared to be more intense at our sites than previous reports. Understanding how the intensity of larval damage impacts Canada thistle plants over time is critical to understanding the relevance of these insects for weed biocontrol.