While it is know that the color of traps in insectivorous plants can alter their prey capture rate, but the mechanism associated with trap color variations and their trapping function is not known. In this study, we used Dionaea muscipula to test whether the color of the flytraps and their fly catching ability could be related to substrate nitrogen levels.

Dionaea were grown in 8 different NaNO₃ treatments, ranging from 0.0 to 3.5 mg/l given at 75 ml per plant once every two days. After 1 month, clear color differences ranging from green to dark red in new and existing flytraps were observed. Anthocyanin concentrations of the traps were measured, followed by a prey-capture efficiency test. Fruit flies were released in an enclosure with three Dionaea plants, each with flytraps that are mainly deep red, light red and green, respectively, and their fly capture rates were recorded.

We found a significant correlation between substrate nitrate level and anthocyanin concentration (R²=0.90) indicating that anthocyanin level increased under low nitrate conditions, producing darker red flytraps that captured significantly more flies than the light red and green traps. We conclude that Dionaea growing in low N environments respond by producing more anthocyanin which reddens the flytraps that catch more flies (by making them more attractive to prey species) thereby effectively supplementing their lack of N.