Insects that live in aquatic habitats can be sensitive to pollution. Mayfly larvae are especially sensitive to toxic metals and can disappear from waters they once inhabited if the levels of pollutants are high. Compared to mayflies, caddisfly larvae are typically more tolerant of many pollutants, especially heavy metals. Caddisfly larvae will accumulate heavy metals such as Cu, As, Zn and Pb in their tissues. High concentrations of the same metals can kill Mayfly larvae. This has led to a number of proposals for ways to use insects as sentinels for the health of our environment.
A recent study by Rainbow and colleagues correlated the concentrations of the heavy metals, Cu, As, Zn and Pb, that bioaccumulate in a species of caddisfly, Hydropsyche siltalai, to the populations of mayflies. They found a positive correlation between metal concentrations in the caddisfly larvae and mayfly populations. At the highest metal bioaccumulations in the caddisfly larvae, mayfly larvae were absent from the water. At the lowest metal bioaccumulations, mayfly larvae are present.This has potential use for informing stream remediation. Mayfly larvae can disappear for a variety of reasons, such as temperature shock, pesticides or other toxic chemicals that are transient in the environment. Identifying the causes of the local mayfly extinctions is an important first step in the remediation process. Analysis of caddisfly larvae could confirm that heavy metal contamination is an important factor in the disappearance of a mayfly population. We can then direct attention on prevention and remediation to remove heavy metals from the environment.