- We tested the hypothesis that a negative fitness-density relationship exists in haematophagous ectoparasites. We studied the effect of flea density on the number of blood meals necessary for starting oviposition and egg production in Xenopsylla conformis and Xenopsylla ramesis when exploiting two rodent hosts, Meriones crassus and Gerbillus dasyurus. The number of blood meals taken by a flea prior to first oviposition was similar in both flea species but was dependent on flea density and differed significantly between hosts. When parasitizing G. dasyurus, females of both flea species required a similar number of blood meals to start oviposition, independent of density. By contrast, fleas on M. crassus at higher densities needed less blood meals than at lower densities. Egg production of female fleas differed significantly between flea and host species and was affected by flea density. X. ramesis produced more eggs than X. conformis. When parasitizing G. dasyurus, density did not affect the number of eggs produced by X. conformis, however, when on M. crassus, this flea produced significantly less eggs at the highest density. The number of eggs produced by X. ramesis at high densities was significantly lower than at low densities when it parasitized either host species. Results of this study demonstrated that reproductive success of fleas was density dependent and, in general, decreased with an increase in density. However, the effect of density on reproductive performance was manifested differently on different host species.