Life history strategies often shape biological interactions by specifying the parameters for possible encounters, such as the timing, frequency or way of exposure to parasites. Consequentially alterations in life history strategies are closely intertwined with such interaction processes. Understanding the connection between life history alterations and host-parasite interactions can therefore be important to unveil potential links between adaptation to environmental change and changes in interaction processes. Here we studied how two different host-parasite interaction processes, oral and haemocoelic exposure to bacteria, affect various life histories of the Glanville fritillary butterfly Melitaea cinxia. We either fed or injected adult butterflies with the bacterium Micrococcus luteus and observed for differences in immune defenses, reproductive life histories and longevity, compared to control exposures. Our results indicate differences in how female butterflies adapt to the two exposure types. Orally infected females showed a reduction in clutch size and an earlier onset of reproduction, whereas, a reduction in egg weight was observed for haemocoelically exposed females. Both exposure types also led to shorter intervals between clutches and a reduced life span. These results indicate a relationship between host-parasite interactions and changes in life history strategies. This relationship could cast restrictions on the ability to adapt to new environments, and consequentially influence the population dynamics of a species in changing environmental conditions.