Friday, January 19, 2001
Observations on Carlisle ecology and mosquitoes: January, 2001
Nancy and I have lived in Carlisle since 1969. We built a house on land we bought in 1965 near the Spencer Brook marsh at the corner of South Street and West Street. We have been watching the changing ecology of that part of Carlisle since 1965 both out of interest and because we were perforce part of it. We think that what we have observed is relevant to the question of mosquito control and, apparently, not well known. We would like to put our observations on record.
About the time that we bought the land, opposition to widespread insecticide spraying was growing on the basis of concerns about human and wildlife health. Predictably, the first and most notable change as spraying was reduced was an explosion of the insect population. However within a few years the population of small birds grew rapidly and there was a noticeable reduction in insects. The small bird expansion was followed by the appearance of larger birds and mammal predators. For about fifteen or twenty years there seemed to be a series of entrances of animals, each higher on the food chain than the previous wave.
This regular series of waves became less orderly as the higher predators became more established. The ups and downs of different species' populations seemed to be affected by disease and other factors which were not obvious. However we are still undergoing this process as evidenced by the more frequent sightings of bears and eagles.
Through all of this, mosquitoes remained a terrible pest. They swarmed all over our screens, infiltrated the house constantly and made outdoor activity impossible except during bright, sunny periods. The problem was most apparent in the spring and was ameliorated as birds, especially swallows got to work. The big consumers of mosquitoes were dragonflies, however. Dragonflies knock the mosquito population down enormously as soon as they arrive.
All this changed mysteriously about three or four years ago. We began to notice that there were fewer mosquitoes during the day and night. In the past two or three years it has often been possible to walk outside after dark without protection. This was unheard of before then. Even in the summer of 2000 the mosquitoes did not represent much of a problem. Previously, such wet conditions created a mosquito hell. Although we are mostly referencing the Spencer Brook area, we have anecdotal confirmation of similar observations by people in other parts of town. We personally have noticed a relative dearth of mosquitoes at Great Brook Farm and other conservation lands.
We are not ecologists and we have no explanation for this sudden reduction in the mosquito population. It doesn't seem to be correlated with the dragonfly population which qualitatively appears to have remained about the same for the past ten years or so. And it is possible that the trend will reverse. However, it seems clear that the present relief from mosquito problems is the result of about thirty years of ecological evolution after the ending of widespread spraying. If we begin spraying again, we may very likely set the ecology back to where it was thirty years ago. Not only would this eliminate much of the ecological richness which we now enjoy, but it might return the mosquitoes to their former glory. Then the only way to bring them to the present level would be a truly massive spraying program.
© 2001 The Carlisle Mosquito