Riodinidae

Riodinidae is the family of metalmark butterflies. The common name 'metalmarks' refers to the small, metallic-looking spots commonly found on their wings. The 1532 species are placed in 146 genera. Although mostly neotropical in distribution, the family is also represented both in the Nearctic and the Palearctic. The family includes small to medium-sized species, from 12 to 60 mm wingspan, often with vibrant structural colouring. The wing shape is very different within the family. They may resemble butterflies in other groups, some are similar to Satyrinae, some are bright yellow reminiscent of Coliadinae and others (examples Barbicornis, Rhetus arcius, Helicopis, Chorinea) have tails as do Papilionidae. The colouration ranges from muted colours in the temperate zone species to iridescent blue and green wings and transparent wings in tropical species. The golden or silvery metallic spots on the wings in many species of the Americas gave them the English common name 'metalmarks'. A number of species mimic poisonous moths of several families and there are often extensive mimicry rings of similar-looking species, grouped around a model. Mimicry causes often closely related species to have completely different wing patterns, for example the genus Thisbe. Many species mimic the stain and stripe pattern of toxic Nymphalidae. Batesian mimicry seems to be more common than in any other insect family of similar size. Reasons for this are unknown. Another example is Ithomeis where different subspecies resemble the species they mimic in different parts of the geographic range more than they resemble each other. The delimitation from the closely related Lycaenidae by morphological autapomorphy is difficult. The first pair of legs of the males, which arises on the prothorax, is less than half as long as the legs of the pterothorax and they are not used for walking. The individual segments of the tarsus are sometimes fused together and fused with the tibia, and the pretarsi have no claws. This feature is also found in some Lycaenidae (and also the Monotrysia), but in these the legs are always much longer. The sensory hairs on the tarsi of the female forelimbs are arranged in a group. These groups which are arranged in pairs can be found in the other taxa of the Papilionoidea. The third problematic apomorphy is the absence of the rear projections (apophyses) of the female genitalia. This feature (absence) is found as well in some species of the subfamily of Poritiinae. In almost all Riodinidae, the coxae of the front legs are extended on males jutting out over the trochanter (only hinted at in Styx infernalis and Corrachia leucoplaga). If there are similar projections in Lycaenidae (in genera Curetis, Feniseca and Poritia), they are built differently in detail and may be, for example, dorsally convex. In addition, almost all Riodinidae in contrast to the Lycaenidae have a humeral vein in the hindwings and the costa is thickened (exceptions in the subfamily Hamearinae). The head in relation to the eyes is wider than in Lycaenidae, making the antennal bases further away from the eye. The relatively long antennae often reach half of the front wing length. Riodinidae have an unusual variety in chromosome numbers, only some very basal groups have the number typical for butterflies (between 29 and 31) or the number characteristic of Lycaenidae (23 to 24). Numbers between 9 and 110 occur. In some cases, representatives of a morphologically indistinguishable cryptospecies have different chromosome numbers and are reproductively isolated. Like the lycaenids, the males of this family have reduced forelegs while the females have full-sized, fully functional forelegs. The foreleg of males is often reduced and has a uniquely shaped first segment (the coxa) which extends beyond its joint with the second segment, rather than meeting it flush. They have a unique venation on the hindwing: the costa of the hindwing is thickened out to the humeral angle and the humeral vein is short. Riodinidae is currently treated as a distinct family within the superfamily Papilionoidea, but in the past they were held to be the subfamily Riodininae of the Lycaenidae. Earlier, they were considered to be part of the now defunct family Erycinidae, whose species are divided between this family and the subfamily Libytheinae. Today, most systematists prefer to accept an independent family even if there are counter arguments. Based on morphological studies Ackery et al. in the manual of zoology (Kristensen 1998, cf. literature) placed Riodininae within the Lycaenidae. Kristensen et al. accepted the updating of the manual in 2007 raising the classification to family rank at least on a provisional basis.