Abstract.1. Population size as well as the absolute and relative frequencies of thephegeaandfilipendulaemimetic complexes have been estimated in an area of Central Italy selected because it is: (a) little affected by man, (b) representative of many others in the Central Appennines, and (c) containing an abundant population ofZygaena ephialtes.2. This distasteful polymorphic species belongs, in Central Italy as in other Southern areas, to thephegeacomplex (Zygaena ephialtes, yellow ephialtoid form), while in Northern and Central Europe it belongs to thefilipendulaecomplex (Z.ephialtes, red peucedanoid form).3. In the Southern areas thephegeacomplex is much more abundant than thefilipendulaeone, which gives the yellow ephialtoid form ofZ.ephialtesa strong mimetic advantage over the red peucedanoid.4. In addition,Amata phegeagreatly outnumbers the other distasteful members of its complex and emerges first.5. Throughout its flight periodZ.ephialtes, which emerges about 20 days later thanA.phegea, never attains a frequency higher than 0.03 in this complex. It is suggested that in such a situation the protection that this species gains as a mimic would be very high regardless of its unpalatability.6. These findings and others discussed in the present paper, such as the degree of unpalatability, the genetics of the mimetic form as well as the polymorphism for colour and pattern, are examined according to the hypothesis of divergent evolutionary strategies in Batesian and Müllerian mimicry. It is suggested that these are meaningful concepts but that individual mimics, of whichZ.ephialtesis one, can fall between them