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Yes, they're pests, but they serve a purpose too


May 27, 2009
LAKES REGION — They say the only guarantees in life are death and taxes. Here in New Hampshire we can add black flies to the list.

Each year a sub-season of sorts hits the area as these tiny pests hatch and invade our state. Swarms of flies hover over people, livestock and wildlife in search of a feast.

Born from beneath running waters each spring, the hatches begin to appear as temperatures in their watery womb hit 40 to 50 degrees. When the larvae hatch, they cling to aquatic plants in the streams and actually do some good.

The larvae (the middle lifestage between eggs and the adult fly itself) are filtering creatures. While hanging onto their perches in the water, they feed on bacteria and other microorganisms in the streams and rivers. By removing these particles of vegetative and bacterial growth they clean the water. N.H. Large Lake Fisheries Biologist Donald Miller said that the presence of black flies indicates a healthy body of water.

"Black flies are a great indicator of good water quality," he said. "They need pure, well-oxygenated water in clean-flowing streams. They filter out a lot of suspended material that is found in our streams and ultimately utilize it as food."

Again, this is good and bad news. This larva in turn becomes food for fish and other aquatic animals in the streams. Well-fed fish are great for the sportsmen with rod and reel in hand. By the same token, large numbers of larvae also hatch into large numbers of black flies that plague the streamside fishermen, which perhaps could be the origin of the phrase "You can't win for losing."

Outdoorsmen and gardeners may think the bugs especially prevalent in 2009, but in fact it is not a particularly strong black fly season this far into the spring.

"Due to a dry spring the streams are low, and thus the black fly population will not have a banner year this year," Miller said. "That said, though, there will still be plenty to go around."

Miller enjoys the old adage that "when it's black fly season, it's time to fish for brook trout," and encourages fisherman to grab the bug spray and head out to the streams throughout the state.

Black flies are also a tasty tidbit for birds, swallows and warblers in particular. Bats enjoy a snack of black flies if there is not a tastier moth or beetle nearby, says UNH professor Dr. John Burger.

State entomologists defer to the expertise of Burger when it comes to black flies and mosquitoes. Burger has been involved in studies on these pesky insects for 34 years. He agrees with Miller that this is a typical year, but prefaces his observations by saying that the season depends on where you are in the state.

"Here in Durham the season is slowing down, but the further north you go, the temperatures have been cooler and places like Colebrook are still quite populated with black flies," Burger said. "The season tends to slowly make its way north so some areas have more flies at this time (than the Seacoast does)."

Early spring Burger calls a "pestiforous" time of year, but shares the same ecological viewpoints on the pests as Miller. They do serve a purpose in a stream's ecosystem and health that most do not realize. He does not feel this has been an unusually populous black fly season either and points out that despite what humans may think, there are only a small percentage of the flies that will actually end up biting. With large numbers hatching however, that percentage can nonetheless seem like many, even if only half of them should bite.

Mosquitoes are a different story in the insect world. There isn't a real "up side" to them unless they happen to be a part of your daily diet. Dr. Burger says that these flying insects come in many species and all do bite. Some winter over as larva, some early risers seen each spring spend a dormant winter in the adult stage, some do not hatch until snowmelt, and yet another breed hatches in late summer. Rainfall in July and August regulate how much of an impact the late summer breed will have on the state. It is this mosquito that state officials monitor for diseases such as EEE (Eastern Equine Encephalitis).

"It's hard to say what kind of impact EEE will have in N.H. this year," said Burger. "That will depend on samples from mosquito pools collected later in the summer."

While he could not recall a case of EEE in a human here in this state yet, Massachusetts did register some cases last year. People are urged to take precautions to prevent any instances of the disease.

The best advice Burger could offer on these biting insects is to remember to have the bug spray handy and to use it. People should also remain mindful of the fact that, unlike black flies who prefer running water, mosquitoes will utilize standing water in even the smallest puddle or ground depressions to lay their eggs. Residents should survey their yards for anything that could hold water and remedy the situation to avoid it becoming a mosquito "nursery." Protection with products containing DEET is the best form of defense against black flies and mosquitoes, as well as ticks, which are now beginning to show up on humans and pets. Deer flies are another species of biting pests, which will hatch on the edges of waterways. These are also beginning to make their annual appearance in the southern reaches of the state.

"The black flies will be around for a bit longer, depending on where you are in the state," Burger warned. "But then the mosquitoes are already showing up, too. How bad will they be? I'll let you know when the summer is over! You just can't predict that in advance so get out the 'bug dope' and be ready."

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