Mercury is a toxic metal that can accumulate in aquatic organisms. Sources of mercury include mine drainage, manufacturing, and power plant emissions. People want to know if fish from a lake or stream are safe to eat. The answer requires sampling aquatic organisms to determine the mercury levels. Collecting and testing insects can be significantly less expensive and more efficient than testing the fish themselves. This can allow sampling to be expanded to more locations. Water striders are relatively easy to locate, collect and test for mercury. Levels of mercury in water striders can tightly correlate (> 0.8) with mercury levels in fish.* This makes water striders a useful sentinel for quantifying mercury contamination.
*Timothy D. Jardine, Tom A. Al, Kerry T.B. MacQuarrie, Charles D. Ritchie, Paul A. Arp, Antu Maprani, Richard A. Cunjak. 2005. Water striders: mercury sentinels in small freshwater ecosystems. Environmental Pollution. 134: 165-171. http://dx.doi.org/10.1016/j.envpol.2004.07.006.