A research group has revealed a new system that allows them to control the behavior of the nematode worm Caenorhabditis elegans, using two different animal opsins, a type of light-sensitive protein. The first opsin was expressed in the worms’ sensory cells responsible for triggering avoidance behavior, making the worms move. This opsin was found to be approximately 7,000 times more sensitive to white light than the commonly used optogenetic protein channelrhodopsin-2. Likewise, a UV-sensitive opsin was expressed in the worms’ motor neurons, causing the worms to stop when exposed to UV light and start moving again when exposed to green light. Both opsins tested can be switched on and off repeatedly without breaking down, making them robust tools for future research, including the field of drug discovery.