The two British oaks support some 439 species of parasite directly, and indirectly many hundred more which parasitise these parasites. "It would certainly be an underestimate to say that the two British species of oak are the primary products for a thousand species of parasite". Obviously, the large size of these trees is a factor in the number of parasite species. In general, this holds whether the host is a plant or an animal. A larger bird will harbour more species of ectoparasite than a small bird.