The study was done during the spring, summer and fall of 1998 and 1999. Samples were taken at random from legume crops and spontaneous plants adjacent to them in the province of León (Spain). Observations were made on the following crops: Medicago sativa, Phaseolus vulgaris, Pisum sativum, Cicer arietinum, Trifolium repens, Vicia fava, Trifolium pratense, Vicia ervilia, Lathyrus cicera, Lathyrus sativus, Trigonella foenum-graecum, Lupinus albus, Lupinus angustifolius and Lens esculenta. Twenty three families of spontaneous plants were observed. The aphid species and their population densities on the spontaneous plants and crop plants were recorded, as was the presence of members of the families Coccinellidae, Syrphidae and Chrysopidae. The plant families Brassicaceae, Asteraceae and Chenopodiaceae had the greatest numbers of these natural enemies of aphids the manipulation of spontaneous plants in agrosystems is a potential means of increasing populations of natural enemies of aphid pests in legume crops.