Knowledge of the biology of signal flies is inadequate and scattered, with that for the genus Rivellia being better than other genera, but yet still insufficiently documented. This paper draws together the collective information on the biology of Rivellia, especially since many species attack root nodules of legume crops around the world. The growing economic importance associated with this biology hinges on increased demands for legume crops, especially soy, which is not only used in human food supply, but also as stock feed that indirectly benefits the human food chain. At least 22 species of Rivellia are associated with root nodules of legumes, including 32 different plant species interactions and many more varieties among these. Of these, seven species impact on the soybean Glycine max (L.) Merrill trade, which amounts to a global production of nearly 350 million tonnes per annum, accounting for 56% of worldwide oilseed production with a market value of in excess of USD48 billion. So significant is the pest association of one species, R. quadrifasciata (Macquart, 1835), that it is known as the Soybean Nodule Fly (SNF). Indications from species analysis in the USA are that Rivellia species associated with root nodules of legume crops have shifted from a primary indigenous meadow legume to the mono-cultured crop species.