Sixteen years ago, a schoolteacher from New Jersey collected a caterpillar in a Costa Rican rainforest. When a parasitoid emerged several days later, it became the first data point of a long-term volunteer–mediated study on tritrophic interactions across the Americas. The teacher was an Earthwatch Institute scientist and the project an ongoing ecological investigation of caterpillars, host plants, and the wasps and flies (parasitoids) that kill them (Fig. 1). Over the course of 16 years, 1,200 volunteers have contributed to the project, including adult and youth citizen scientists from Earthwatch, teachers, and a number of other volunteers who have offered their time for months or years.