Pitcher plants possess extrafloral nectaries that secrete nectar containing sugars, amino acids, and water to attract nectivorous prey such as ants. Other factors have been hypothesized to attract prey: the intricate red patterning (anthocyanin pigment) on the pitcher walls, and the fragrance of decomposing prey inside. To test the effects of nectar, anthocyanin density, and detritus fragrance on the pitcher plant's ability to catch prey, we conducted a field experiment using Sarracenia purpurea (northern pitcher plants) in a Massachusetts bog in summer 2009. Fifty pitchers with an incremental range of red patterning density were chosen and analyzed for prey capture. We also analyzed nectar quantities in the fifty plants using filter paper wicks and a standard colorimetric method.
To augment our results we conducted a series of prey capture experiments in the same bog using 80 pitcher mimics (pseudopitchers): 50 ml centrifuge tubes, their outsides painted with varying densities of red patterning to mimic the anthocyanin pigment on a pitcher. Half of the pseudopitchers were treated with a sugar solution to mimic the presence of nectar. Half of the pseudopitchers were filled with strained liquid from live pitchers to test the impact of the fragrance of decomposing prey.
For all prey orders analyzed (ants, flies, and springtails) the rate of capture by psuedopitchers and real pitchers did not differ. The proportion of visible red area in live pitchers and psuedopitchers did not affect prey capture rates. Presence of a sugar solution increased ant capture rates in psuedopitchers. (p<0.005). Psuedopitchers with decomposing capture fragrance tended to capture fewer ants than control psuedopitchers. (p=0.06). No other prey orders were affected by fluid composition. Our preliminary results illustrate that nectar is an important determinate for the capture of ants- the primary prey of Sarracenia purpurea- but ants may actually be repelled by the fragrance of prey decomposing inside the pitchers.