The genus Phosphaenopterus encompasses two species restricted to Europe, both underrepresented in the literature and entomological collections. Phosphaenopterus metzneri is the most widely distributed within the genus, being recorded in France, Portugal, and Spain. Since its century-old original description based only on the male, the biology of this species was not further investigated. By collecting larvae of Phosphaenina where male of Phosphaenopterus metzneri occur, we reared them to adults, resulting in male and females of Phosphaenopterus metzneri – the latter hitherto unknown. The male-female association was possible due to copula recorded ex-situ. Here, we describe for the first time the neotenic female of Phosphaenopterus metzneri, a diurnal firefly, and redescribed the male. We provide illustration of diagnostic features of the adults, and an updated distribution map for Phosphenopterus metzneri. Considering the morphological resemblance between all the three species within Phosphaenina, we also redescribe the male of Phosphaenus hemipterus (), a species also presents in Portugal, providing important diagnostic features for both taxa. By comparing the morphology of males of Phosphaenus hemipterus and Phosphaenopterus metzneri, we could not find any difference other than proportions of elytra, and wings, which may be a result of the brachypterous condition of the former. This study stresses and discusses a putative case of wing polymorphism in Lampyridae, a rare condition in fireflies. This is also the first study to report both species in sympatric distribution.