Camponotus ants mine sand for vertebrate urine to extract nitrogen

The ability of some ant species (including Camponotus spp.) to forage on vertebrate urine to extract urea may extend their niche in competitive and strongly nitrogen-limited environments. We examined the preference of Camponotus terebrans, a sand-dwelling ant widespread in southern Australia, for baits including urine, and the duration of their foraging on those baits. We baited ants with liquid stains of urine (human and kangaroo), urea in water (2.5%. 3.5%, 7.0%, 10.0%) and sucrose in water (20% and 40%) poured directly on the ground, as well as hard baits in plots drawn on sandy soil (Kangaroo Island, South Australia). We counted individuals of this mostly nocturnal species to determine their attraction to different baits for one month. We checked plant growth on the plots after nine and 13 months. Ants collected insects and meat; they foraged for at least 29 days on stains. Ants were most numerous on 10% urea, followed by 7% urea, 3.5% urea, urine (which contains similar to 2.5% urea) and 2.5% urea, 40% sucrose and 20% sucrose; sucrose was less attractive to them than equimolar urea bait. Ants were attracted to human, kangaroo, and unidentified urines, and they collected bird guano. Baits and ant foraging did not affect plant recruitment in plots. We observed incidentally Camponotus consobrinus foraging on urine, which may be a common resource for this genus at the site. The remarkable ability of C. terebrans to extract nitrogen from dry sand over weeks explains partly its success on sandy soils. Foraging on urine may be an important strategy to address nitrogen limitation on sandy soils and exploit commensally niches in which hosts are kangaroos, wallabies and other vertebrates. The understanding of plant-vertebrate interactions must factor in the role of ants as commensal organisms. Such ants could also reduce greenhouse gas emissions from urine.