Prey capture in the Venus flytrap: collection or selection?

Charles Darwin first proposed that the Venus flytrap (Dionaea muscipula Ellis) functions optimally by capturing and digesting large prey, the small prey escaping through openings at the trap margins. This hypothesis, although intuitively sound in the context of trap mechanics or plant allocation theory, has not been tested adequately with populations of plants growing in the field. Here, with traps collected in the endemic habitat over 9 months, we show that prey capture in the Venus flytrap is opportunistic rather than selective. While there was no effect of trap size on prey capture success, there was a significant but weak positive relationship between trap length and prey length. Prey sizes were well below the theoretical maximum holding capacities of traps and relatively small insects were represented across the range of trap sizes. Our results show that prey capture was not biased toward large invertebrates. Instead, we suggest that nonselective prey capture across the observed range of trap sizes is the best-fit explanation of trap function in the context of relatively limited ability to change allocation in response to sudden increases in resource availability.