Anomalies in hydropsychid capture nets from polluted streams

Members of the genus Hydropsyche, net‐spinning caddisfly larvae, exhibit anomalies in the structure of their capture nets when collected from stream localities receiving heavy metal and toxic chemical wastes. The number of nets showing anomalies was positively correlated with the number of anomalies per net suggesting a graded response to the toxic wastes. Frequency of anomalies in a hydropsychid population increased the closer the nets were collected to a pollution source. Anomaly frequency was negatively correlated to total macroinvertebrate community structure as measured by the Shannon function. It is suggested that net anomaly frequeney by hydropsychids may be a useful tool in ecological monitoring.