Local and long-distance labour migrants were an important element in commercial groundnut farming along the Gambia river during the mid-nineteenth century, well before colonial partition. Seasonal and periodic circulation of migrant farmers had prior equivalents in the movements of traders across the Western Sudan, especially those associated with slaving. Traders were important in the development of groundnut cultivation and the initiation of migrant farming, when they realized the groundnut trade could be a valuable replacement for the abolished slave trade. In the pre-colonial era migrant farmers payed ‘custom’ to local rule for the land they farmed. This arrangement eventually gave way to a system of shared labour-time with individual host farmers in return for land. This change was accelerated by the abolition and decline in domestic slavery, which provided a new pattern for the Strange Farmer system. Thus the mobility of population in the Western Sudan, together with the evolution of the Strange Farmer system, provided vital marginal inputs of labour in an area of low population densities and facilitated the development of groundnut farming during the era of legitimate trade.