The identification of micro-organisms carried by ticks is an important issue for human and animal health. In addition to theirrole as pathogen vectors, ticks are also the hosts for symbiotic bacteria whose impact on tick biology is poorly known.Among these, the bacterium Wolbachia pipientis has already been reported associated with Ixodes ricinus and other tickspecies. However, the origins of Wolbachia in ticks and their consequences on tick biology (known to be very diverse ininvertebrates, ranging from nutritional symbionts in nematodes to reproductive manipulators in insects) are unknown. Herewe report that the endoparasitoid wasp Ixodiphagus hookeri (Hymenoptera, Chalcidoidea, Encyrtidae) – strictly associatedwith ticks for their development - is infested at almost 100% prevalence by a W. pipientis strain belonging to a Wolbachiasupergroup that has already been reported as associated with other hymenopteran parasitoids. In a natural population of I.ricinus that suffers high parasitism rates due to I. hookeri, we used specific PCR primers for both hymenopteran and W.pipientis gene fragments to show that all unfed tick nymphs parasitized by I. hookeri also harbored Wolbachia, whileunparasitized ticks were Wolbachia-free. We demonstrated experimentally that unfed nymphs obtained from larvaeexposed to I. hookeri while gorging on their vertebrate host also harbor Wolbachia. We hypothesize that previous studiesthat have reported W. pipientis in ticks are due to the cryptic presence of the endoparasitoid wasp I. hookeri. This associationhas remained hidden until now because parasitoids within ticks cannot be detected until engorgement of the nymphsbrings the wasp eggs out of diapause. Finally, we discuss the consequences of this finding for our understanding of the tickmicrobiome, and their possible role in horizontal gene transfer among pathogenic and symbiotic bacteria