The acidic fluid present in the traps of Nepenthes pitcher plants has a primary function of digesting prey, but also plays a role in the capture of insects. Bazile et al. collect fluid in the field from pitchers of four Nepenthes species and determine retention capacity and time-to-kill for different species of ants and flies under controlled conditions. They find that both the pH and viscoelasticity properties of the fluid influence a plant’s diet and its carnivorous status. Thus the plants may select the prey that they retain by manipulating the secretion of H+ ions and polysaccharides in their pitcher fluid, which has implications for potential adaptive radiation of this genus with regard to the nutrient sequestration strategies of different species in various habitats.