Purple martins and mosquitoes
By By Robert A. Hedeen, Naturalist
In 1962 Rachel Carson published the book Silent Spring that alerted the public to the dangers of the widespread, indiscriminate use of persistent pesticides. As a result of her monumental work, a renewed interest in the biological control of insects and other animals of medical and economic importance was sparked. Biological control is the use of one organism to control another.
Mosquito control before the publication of Silent Spring was based primarily on the use of long-lasting broad-spectrum insecticides (such as DDT, Mehoxychlor, Chlordane) and by the manipulation of the landscape by draining and filling of mosquito breeding areas. About the only biological control method employed by mosquito abatement agencies was the planting of mosquito larvae-eating fish in permanent impoundments of water.
Then the purple martin was introduced to an anxious public as the magic bullet for relief from the pestiferous and sometimes dangerous mosquitoes. No longer did we have to rely on toxic and dangerous chemicals to do the job. Martins were touted as the answer to the problem as they were said to eat 40,000 or more adult mosquitoes each day. No scientific study was offered to substantiate this figure.
Purple martins are delightful birds. In the South, the mocking bird is probably the favorite bird, and in the North the cardinal or robin would probably win first prize in a popularity contest. But, on a nationwide basis, the purple martin is the most celebrated of our feathered-friends
Purple martins, the largest of the swallows, have been cherished and encouraged for hundreds of years. Recognizing their value in abating insect populations and believing their presence brought good luck, Indians attracted these birds to their villages by hanging out large, dried gourds to be used as nesting sites. The early white settlers continued this practice, and their descendents went on to make many architectural improvements in martin houses, though in rural areas today, one frequently sees gourd martin houses hanging from a crossbar in the yard of a dwelling.
The range of the purple martin is extensive, almost universal. Indeed, it occurs from coast to coast and border to border. It is a migratory species, spending the winter in parts of South America. In the spring, scouts cross the Gulf of Mexico and seek out nesting facilities in North America. The scouts remain in the area awaiting the arrival of the main flocks to show where nesting sites are located. Once a group of martins nests in a specific location one year, the homing instinct is activated, and they will undoubtedly return to the same area the next year.
The fear of pesticides generated by Silent Spring and the fact martins feed almost entirely on flying insects prompted some entrepreneurs to go into the business of manufacturing purple martin houses. Somehow, the figure of martins devouring 40,000 mosquitoes a day was invented, and all the homeowner had to do was to purchase and erect a martin house on his property, and the pesky blood-suckers would be eliminated.
The small town of Griggsville, in west-central Illinois, proudly proclaimed itself to be The Purple Martin Capital of the World. It was not mentioned that one of the principal businesses in Griggsville was the manufacturing of aluminum martin houses and telescoping poles upon which the houses could be mounted in ones backyard.
But, the basic question is do martins destroy sufficient numbers of mosquitoes to reduce their population numbers to a tolerable level? Numerous studies have proven that the answer is emphatically no!
As far back as 1918, Dr. F.E.L. Beal, a distinguished ornithologist, made an extensive study of the food habits of the purple martin. Beal examined the stomach contents of thousands of martins from widely scattered areas and found that all types of flies (mosquitoes are only one of the hundreds of types of different flies making up this order of insects) made up only 15 percent of the martins daily intake of food. Bees, wasps, butterflies, moths, bugs, beetles, dragon flies and a host of other insect forms made up the other 85 percent. The inflated figure of 40,000 mosquitoes a day is proven to be a myth, conjured up by the manufacturers and retailers of purple martin houses. Certainly, a martin will take in a mosquito if it runs into one, but the numbers of the blood-sucking gnats devoured is insignificant. Additional research on the 40,000 question has confirmed Beals data and conclusions.
Be that as it may, we should encourage purple martins whenever and however possible. They are beautiful birds and thrill us with their wonderful aerobatic maneuvers as they zigzag across the environment filling their bellies with flying insects, both useful and destructive.
Dr. Beal stated that in his studies of the purple martin and its feeding habits, he encountered only one person who was not fond of this desirable bird. That individual was a recent German immigrant farmer who complained that the martins ate all of his peas. As Beal had neither observed nor heard of martins feeding on peas, he questioned the man further and determined he meant bees. Apparently, the man was at odds with the martins for devouring the honeybees he maintained on his farm
Encourage and enjoy the purple martin, but dont forget to use repellent.
Dr. Robert Hedeen is a former resident of eastern Maryland, with degrees in zoology and botany. He is a former professor of biological science. He has had 30 scientific papers published, has written numerous magazine articles, and is the author of two books on marine biology of Maryland.