Iolaus silarus, the straight-line sapphire, is a butterfly of the family Lycaenidae. The species was first described by Hamilton Herbert Druce in 1885. It is found in Mozambique, Zimbabwe, Botswana, Namibia, Malawi, Zambia, southern Zaire, Tanzania, south-western Kenya and South Africa. In South Africa it is found in wooded savannah in northern KwaZulu-Natal and in savannah from Eswatini to Mpumalanga, Limpopo and North West. It is also present in Afromontane forest on the Wolkberg and the northern Drakensberg.