Abstract Similarity measures are among the most intuitive and common measures for comparing two or more sites, or samples, with respect to their species overlap. A restriction of similarity measures is that they are limited to pairwise comparisons even in a multiple-site study. This work presents a multiple-site similarity measure that makes use of information on species shared by more than two sites and avoids the problem of covariance between pairwise similarities in a multiple-site study. Further, we show that our multiple-site similarity measure is related to β -diversity measures such as Whittaker's β -diversity. Similarity measures can also be used as descriptors of effective specialization of insects to host species by measuring similarity from host observations. Finally, we show that multiple-site similarity and host specificity are two sides of the same coin.