Three species of the genus Eriosoma have been found to have host alternation between Ulmus and Ribes, viz. E. (Schizoneura) ulmi (L.), E. (S.) grossulariae (Schüle) and E. (S.) anncharlotteae Danielsson. The different morphs of the first two species are described and morphometric tables are given to show the variation of certain characters. Keys are given to apterous and alate viviparae of the three species. The hostplant preferences of the different species have been investigated and the more important papers on the biology and morphology of this species complex are reviewed.