The following is a graph of the daily high tides predicted to occur at the Neponset River outflow in Quincy, Massachusetts. The graph is relatively close to the predicted tides elsewhere in eastern Massachusetts, including the Norfolk County Mosquito Control towns of Weymouth, Milton and Braintree. The graph is important for mosquito control because the Salt Marsh Mosquito (Ochlerotatus sollicitans) breeds in accordance with the monthly tidal cycle, as well as rainfall. This mosquito species is probably the most aggressive species in our region, biting during the day as well as night.

The female Salt Marsh Mosquito lays her eggs on areas of the high marsh that are only flooded once a month. During the spring high tide each month (at new or full moon depending on the earth-moon-sun configuration) the eggs hatch in pools of water left by the spring high tide. These larvae then grow through four stages, into a pupal stage, and then emerge as adults. This whole process takes about 7-10 days. Since the tides are very predictable, the emergence of this mosquito is also very predictable.

For residents who live near salt marshes that breed this mosquito, one can use this graph to predict when larger than usual outbreaks will most likely occur. The red dates on the chart represent the date of the spring high tide. Simply add 7-10 days to this date and the mosquito outbreak is predicted. This summer, the likely dates of more severe mosquito outbreaks in Massachusetts coastal towns start around June 12-15, July 11-14, and August 8-11. Unusually large rain events can also trigger salt marsh mosquito emergences. These occurrences are, of course, unpredictable.

The Norfolk County Mosquito Control is active in trying to control these mosquitoes. We annually larvicide the known breeding marshes. Although many mosquitoes are killed, we simply cannot reach all the breeding locations and periodically new breeding sites are created by natural salt marsh dynamics. Check out our link to Open Marsh Water Management (.html / .pdf), a mosquito control and marsh restoration technique that is very effective. We began using this technique in 1999, and have completed 9 projects, six in Quincy and two in Weymouth, and one in Milton.