The larval stage of the trombidioid mites Parafeiderium stuarti n. sp. (family Microtrombidiidae Thor, 1935) and Centrotrombidium blackwellae n. sp. (family Johnstonianidae Newell, 1957) are described. Both species were found parasitising Culicoides impunctatus Goetghebuer, the highland midge (Diptera: Ceratopogonidae), in Scotland. A revised diagnosis for Parafeiderium Vercammen-Grandjean & Cochrane, 1974 and a key to the world species of larval Centrotrombidium Kramer, 1896 are given.