Erikssonia edgei, commonly known as the Waterberg copper, tilodi copper or Edge's acraea copper, is an obligate myrmecophylous lycaenid butterfly, which is native to Limpopo, South Africa. The critically endangered butterfly occurs in high-altitude grasslands on sandy substrates, and has only been obtained from the type and one subsequent locality. The population at the type locality, a farm in the Waterberg, went extinct about 12 years after its 1980 discovery. It was afforded species status in 2010, when no extant populations were known. The status of two populations, discovered in 2013 at a private nature reserve to the southeast, remains indeterminate. Description and biology The forewing length is 12.3-16.8 mm for males and 16.1–19.1 mm for females. It was found to be closely related to the Aloeides rough coppers (cf. A. dentatis and A. thyra) and like them, is associated with ground-nesting ants. The larvae feed on two species of Gnidia, both poisonous, and shelter by day in the nests of Lepisiota ants, wherein the pupae also develop. Adults are on wing from November to April. They fly slowly and weakly in the vicinity of their host plants, and dive into the grass when disturbed. The males are territorial during the warmer hours of the day, but the females not. They like basking in the sun, and often feed on nectar, but not during the hours devoted to territorial behaviour or egg-laying. In cool cloudy weather they may be found resting on the sand between grass tufts. Egg-laying A female that is ready to oviposit will investigate the surfaces of plants with her antennae. When she encounters the food plant she uses her antennae to search for traces of the trail pheromones of the host ant. Upon encountering this, she will walk down until she reaches the ground at the base of the plant. There she will oviposit the yellowish ochre eggs by curving her abdomen down to the ground surface. The eggs darken to greyish brown, and their appearance has been likened to a truffle. Their micro-structure is considered quite unique among lycaenid eggs. Ants carry the eggs into the nest where the larvae hatch in about 18 days, and congregate with the ant brood. Instars The different larval instars are fairly uniform in appearance. They have pinkish grey bodies with a maroon line down the dorsum, flanked by bluish green and regular reddish brown markings on the sides.