The king ragworm (Nereis virens) is a polychaete worm that lives in burrows at the low water mark on intertidal beaches. Here, Kim Last and colleagues kept these worm in specially designed ‘burrows’ made from plastic tubing, at the bottom of marine aquaria (yellow arrows in main image). The tanks were given simulated tides by pumping seawater in an out on a 12.4h cycle to mimic natural conditions. Each burrow was fitted with an infrared detector so that when the worm was active and emerged from it’s tube, the beam interruption was recorded. The graph shows beam interruptions over time. These animals were tidally rhythmic but were more active when ‘high water’ coincided with darkness (the tanks were on a natural light and dark cycle too). These methods enabled Last and team to study the worm’s behaviour in controlled conditions.