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No-see-ums (like...biting flies) in Springtime Feeding Frenzy
Julie Tillman never felt a thing.
She didn't see anything, either.
But shortly after the Davis, CA resident returned home from a two-hour outing in Sycamore Park, she noticed her ankles red, bruised and welted.
The culprits: no-see-ums. The tiny valley black gnats ferociously feed on blood -- and they fed on hers.
"This time of year the adults are emerging and go into a major feeding frenzy," said entomologist and insect identification specialist Lynn Kimsey, director of the Bohart Museum of Entomology and chair of the UC Davis Department of Entomology.
The no-see-ums (Leptoconops torrens), so nicknamed because of their near invisibility, are common in parts of California's Central Valley, particularly in areas with alkaline clay soils, Kimsey said.
The adults are black and tiny, about 1/16-inch long, and are small enough to pass through window screens.
"The adults breed when the weather warms up in the spring, usually in early or mid-May, and they remain a pest for several weeks," Kimsey said. "When the soil begins to dry and cracks develop, the adults emerge."
Only the females bite. Like female mosquitoes, they need a blood meal to complete their reproductive cycle. No-see-ums bite humans, animals and birds.
Kimsey said they have short mouthparts and the females feed by injecting saliva into the skin, which pools the blood just beneath the surface.
"The bite is generally painless, but usually results in a small flat red spot that, within 12 hours, becomes excruciatingly itchy," Kimsey said. A single bite can welt into a one- or two-inch diameter spot, which lasts about two weeks.
"If you scratch it, it will double the length of time and can lead to infected sores," Kimsey said. "It feels so good to scratch, but don't do it. Our fingernails are incredibly dirty."
Tillman, an insect biochemist by training and also a freelance Web designer, estimated she received 200 bites on each ankle on May 2. As of May 15, she continues to have welts. Husband Steve Seybold, a USDA Forest Service entomologist based at the Pacific Southwest Research Station in Davis, says her ankles "look like hamburger."
Tillman, who at the time wore short socks, tennis shoes, knee-length pants and a short-sleeved shirt, estimated she sat in the grassy area for two hours. The ferocious no-see-ums bit only her ankles.
"I've had no-see-um bites before -- several at a time -- but nothing like this," Tillman said.
Tillman, who is expecting a baby in October, telephoned Kimsey about the biting attack. Kimsey assured her that valley black gnats don't transmit diseases.
"There's not much you can do when the black gnats feed," Kimsey said, "except to stay away from them. Don't sit long in places where they are likely to occur or where you've heard they're a problem. Move quickly through the area."
Since the gnats usually fly less than 350 feet from their breeding area, they won't follow you, said Kimsey, who also was bitten by gnats this spring.
"However, the bites are sufficiently annoying to keep people indoors in some areas of California. They're small enough to crawl under loose clothing without being noticed. Standard mosquito repellents do not appear to be completely effective with these gnats."
Senior museum scientist Steve Heydon of the Bohart Museum says he fields calls about biting flies every spring.
"I suspect it might be no-see-ums if I get calls from around salt marshes and in the mountains. I used to do a lot of canoeing on the East Coast and you could always tell when the water turned brackish because the no-see-ums would begin to bite us -- sometimes unmercifully. Some East Coast beaches are unusable because of these flies."
The valley black gnat is one of two species of the biting gnats of the family Ceratopogonidae (Diptera) occurring in California, according to Leslie M. Smith and Homer Lowe, authors of the booklet, "The Black Gnats of California." The other is the Bodega black gnat.
"Unfed gnats are voracious and fearless; they cannot be frightened away from the host," they write. The mouth parts "seem to saw for about 1-1/2 minutes, then the abdomen quickly fills with blood, becoming considerable distended. The host feels no sensation during the first 30 to 60 seconds of the bite; after that a slight tingling is noticeable."
Kimsey said the complete life cycle of the valley black gnat takes two years from egg to adult. Larvae can diapause (a kind of hibernation) for three years or longer, depending on environmental conditions.
On Mother's Day, the Seybold-Tillman family picnicked in the UC Davis Arboretum but they wore long pants and socks, tucking their pants into the socks.
Thankfully, no-see-ums didn't find them.
U of California