The body of vertebrates is inhabited by trillions of microorganisms, i.e. viruses, archaea, bacteria and unicellular eukaryotes, together referred to as the ‘microbiota’. Similarly, vertebrates also host a plethora of parasitic worms (the ‘macrobiota’), some of which share their environment with the microbiota inhabiting the gastrointestinal tract [1]. Complex interactions between the helminths and the gut microbiota have been associated with establishment of parasite infection, disease manifestations, and host immune-modulation [2, 3]. Remarkably, not only enteric helminths alter the 26 gut microbiome composition [4], but also the infection with blood flukes of the genus Schistosoma has been associated to intestinal dysbiosis even before the onset of egg laying [5, 6]. Comparably, over the last decade, evidence has emerged of the contribution(s) of the resident microbiota to several physiological and reproductive processes of invertebrate hosts, including insects, arachnids, worms and snails [7, 8]. These noteworthy discoveries, coupled with 30 the recent expansion of high-throughput microbiota- and microbiome-profiling approaches (the former referring to a community of microorganisms themselves, and the latter to the microorganisms and their genomes, in a ecological niche), are rapidly leading to a much better understanding of the composition and functions of microbial communities inhabiting parasitic worms of major public health and socio-economic significance. This basic knowledge might expose exploitable vulnerabilities of parasites, paving the way to the development of novel control strategies [9].