In an earlier study, laboratory-reared ticks were dropped into the center of a petri dish container with a ring-shaped piece of filter paper treated with a naturally derived repellent, as shown here. Naturally, ticks will either try to escape the space or climb up the walls to seek hosts. However, to do either, the ticks in the study had to traverse the filter paper. The longer it took the tick to venture onto the repellent-laden filter paper, the greater the repellent effect that the plant compound had on the tick. (Photo by Colin Wong, Ph.D.)