Fluid-feeding insects like butterflies and flies are faced with the common selection pressure of having to remove and feed on fluids from porous surfaces. Insects able to acquire fluids from pores during drought conditions would have an adaptive advantage and increased fitness. We performed feeding trials using magnetic nanoparticle solutions to show that butterflies and flies have mouthparts adapted to pull liquids from pores using capillarity as the governing principle. The ability to feed from pores depends on a relationship between diameter of the mouthparts and pore size diameter; insects with mouthpart diameters larger than pores cannot successfully feed, thus there is a limiting pore size from which individuals can acquire liquids for fluid uptake. Given that natural selection independently favored mouthpart architectures that support these methods of fluid uptake, we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling fluids from porous surfaces.