In speciation research, much attention is paid to the evolution of reproductive barriers, preventing diverging groups from hybridizing back into one gene pool. The prevalent view is that reproductive barriers evolve gradually as a byproduct of genetic changes accumulated by natural selection and genetic drift in groups that are segregated spatially and/or temporally. Reproductive barriers, however, can also be reinforced by natural selection against maladaptive hybridization. These mutually compatible theories are both empirically supported by studies, analyzing relationships between intensity of reproductive isolation and genetic distance in sympatric taxa and allopatric taxa. Here, we present the – to our knowledge – first comparative study in a haplodiploid organism, the social spider mite Stigmaeopsis miscanthi, by measuring premating and postmating pre- and postzygotic components of reproductive isolation, using three recently diverged forms of the mite that partly overlap in home range. We carried out cross experiments and measured genetic distances (mtDNA and nDNA) among parapatric and allopatric populations of the three forms. Our results show that the three forms are reproductively isolated, despite the absence of premating barriers, and that the postmating, prezygotic component contributes most to reproductive isolation. As expected, the strength of postmating reproductive barriers positively correlated with genetic distance. We did not find a clear pattern of prezygotic barriers evolving faster in parapatry than in allopatry, although one form did show a trend in line with the ecological and behavioral relationships between the forms. Our study advocates the versatility of haplodiploid animals for investigating the evolution of reproductive barriers.