Midge Sampling and Testing 2020

Under the direction of SPWA Board member Tom Bell, SPWA and local residents are sampling the sediment of Straits Pond this summer for midge larvae to address the seasonal bombardment of midges, a problem that had been mitigated for eight years until 2019. These samples will help determine where the midges are laying their eggs so we can develop plans for improved control. Pairs of samplers are using GPS geo-located sampling site locations as depicted on the map below. Thanks to everyone who has helped with this project. We are looking forward to reviewing these data and developing a better understanding on how to solve the midge infestation on Straits Pond.

Midge infestations around the Pond have been reported for over 100 years.  The Straits Pond Watershed Association played an instrumental role around the turn of the Century to advocate for improved control of the tides through an automated tide gate installed in 2010.  At that time it was thought that increasing the flow of sea water into the Pond would suppress midge populations. For eight years the midge problem was abated as the Pond transitioned from brackish to saline.  It was thought the problem was solved.  In 2018, the automated control of the tide gates failed and the midges returned in force in the spring and summer of 2019 – and again in 2020.  The greatest concentration of midges was around the Pond, but large numbers of midges have been seen as far away as 1,000 ft from the Pond and at an elevation of 100 ft above sea level.   It is not clear that the tide gate failure and the new infestations of midges are related.

The Straits Pond Midge Larva Count was initiated to identify the sites where midges breed and their young (larva) grow to adults to start the next cycle.  We have collected just over 60 samples and are 40% of the way to full coverage of the Pond.  Five two-person teams have made one or more sampling expeditions and others have volunteered to help.  We are already seeing larval concentrations on the west end of the Pond with no sign of larvae on the east end.  There are still about 80 samples to collect and other concentrations may be discovered.

Midge larvae are about ¼” long and very thin. 
Adult midges like shady spots during the day but are attracted to lights at night.
The bottom of the Pond is covered with fine mud the consistency of pudding.  We wash away the pudding then count the midge larvae which are too big to pass through the screen.
After washing, what remains are some plant material, juvenile clams and snails and in some samples, a few midge larvae.

When the midge nurseries are mapped, the next step is to determine which environmental conditions are favorable and unfavorable for their life cycle.  This may lead to a strategy to control their population.  Though adult midges are a nuisance to residents, midge larvae are an important food source for a number of other species around the Pond.  Midge larvae are scavengers who feed on decaying vegetation and serve as an important part of the Pond ecology by breaking down dead plant material and releasing their nutrients for the living.  The ideal solution would be natural control by their predators.  As the Pond becomes even cleaner, more of those predators may thrive and reduce the midge population to a more tolerable level.

Dr Sara Das was among those helping this summer. Dr. Das is a glacialogist at Woods Hole Oceanographic Institute and is doing field work in Greenland and Antarctica. She is navigating to sample sites and record data.
 Samantha Woods is an environmetal scientist and Director of the North and South River Watershed Association. Here she’s taking sample cores from the bottom of Straits Pond. Note the mud sticking out of her core sampler.
We fabricated core sample tools out of PVC pipe that were designed in Vietnam, where they were used to sample shrimp ponds.

Once a core is brought up to surface we extrude the top two inches into a sample bag.

This illustrates the midge life cycle.  We are sampling the mud to count them during their larval stage.
For more information about this ongoing research project, or to join the efforts to collect data or otherwise contribute to the efforts to address the midge infestation on and around Straits Pond, contact Tom Bell: stratamodel@gmail.com