MILLBROOK STP

Eastern Dobsonflies emerge as Millbrook cleanup signal

Eastern Dobsonflies (Nigronia serricornis) are appearing in Millbrook for the first time in recent observations — a remarkable sign of recovery in a stream that has endured serious chemical stress. Their larvae spend three years underwater as nymphs, among the most pollution-sensitive creatures in any freshwater system, filtering through sediment and silt only in clean, well-oxygenated conditions. Last quarter, the Millbrook sewage treatment plant discharged chlorine at nearly 900 times its legal limit — a violation of staggering proportions. That these insects are now maturing and emerging suggests the stream's recovery may be outpacing the violation's damage, though the margin is worth watching closely through the coming seasons.