Kleptoparasitic multiparasitism allows parasitoids to expand their host range to otherwise unsuitable invasive hosts.

Biological invasions frequently disrupt co-evolved host-parasitoid interactions and create evolutionary traps in which native parasitoids attack unsuitable invasive hosts. While escape from such traps has traditionally been viewed as a consequence of adaptive evolution, recent studies suggest that ecological interactions among parasitoids may also enable exploitation of otherwise unsuitable hosts. In particular, increasing evidence supports the occurrence of "pirate parasitism", a specialized form of kleptoparasitism in which one parasitoid species enables another to successfully develop in an otherwise unsuitable host, often through host immune suppression. Here, we review historical and recent studies on pirate parasitism, clarify its conceptual framework, and discuss its ecological and evolutionary implications. Reported cases include both native sympatric systems and invasion-associated systems, suggesting that pirate parasitism may transiently expand realized host ranges, alleviate demographic costs of maladaptive oviposition, and potentially promote rewiring of host-parasitoid interaction networks. We further discuss the possibility that pirate parasitism functions as an ecological bridge between initial maladaptive host use and subsequent evolutionary host range expansion. Finally, we highlight major knowledge deficiencies, including limited evidence from natural ecosystems and unresolved behavioral and physiological mechanisms underlying pirate parasitism. Understanding kleptoparasitic interactions among parasitoids may provide new insights into eco-evolutionary dynamics in rapidly changing environments.