When host organisms mount an immune response, they incur energetic costs. Theory predicts that these costs result in trade-offs between investment in life history traits (such as growth and reproduction) and investment in immune response. Recent empirical work investigating whether immune ability is impaired during sexual activity in invertebrates does not uniformly support this prediction. Here, we use lytic activity to test for trade-offs between immune ability and reproductive events in three experiments with the pholcid spider Physocyclus dugesi (Simon 1893). First, we test whether males or females have their immune response negatively affected after mating; second, we assess whether oviposition behavior affects immune response; and third, we investigate whether sexual aggression by females affects immune response. We compare reproductive and non-reproductive spiders' immune response. Our results suggest a down-regulation of immune response following mating, oviposition, and aggression. This supports the notion that immunocompetence is competing for a resource with sexual activities. We discuss reasons why such costs arise in P. dugesi.