The changing natural world at our doorsteps | By Patterson Clark
June 22, 2010
Dog-day cicadas: Big bugs abuzz
Save for bees humming and mosquitoes whining, local insects are mostly silent until about the first day of summer, when the loudest of them all begins to sing.
Dog-day cicadas are crawling out of the ground as mature nymphs that climb up tree trunks, split open and emerge as long- winged, bug-eyed adults that will live for only a few weeks. Unlike the black-and- orange periodical cicadas, which emerge in overwhelming numbers every 13 or 17 years, the larger, greenish dog-day cicadas are with us every summer.
Males do the droning , which is generated by a pair of ribbed membranes at the base of the cicada's hollow abdomen. Muscles distort these tymbals to make pulses of sound that
resonate in the insect's abdomen. The vibrations from a single cicada can reach 100 decibels and be heard a quarter-mile away.
U.S. Navy scientists, intrigued by the cicada's piercing signal, recently analyzed the efficiency of the insect's sound propagation. "Application of the same principles has the potential to improve radiated sound levels for sonar applications," says a 2009 report.
Male cicadas would prefer to impress a female. If drawn to his call, she will signal her interest with a flip of her wings.
Females use their ovipositor organ to saw small gashes into tree twigs, where they lay eggs. Nymphs will hatch after about six
weeks, drop to the ground, burrow down to a tree root and suck its juices for two to five years before maturing.
Listen to the calls from a few of the species found in the Washington area:
Northern dusk-singing cicada (Tibicen auletes)
Morning cicada, or swamp cicada (Tibicen tibicen)
Scissor-grinder cicada (Tibicen pruinosa)
Sources: Entomology departments of the University of Michigan and the University of Florida; Journal of the Acoustical Society of America.
June 29, 2010
Wineberry's glandular hairs
In late June, the tart, seedy fruits of wineberry begin to ripen, capturing a
few small insects in the process.
The exotic, invasive raspberry was imported from Japan to improve cultivated varieties of raspberry. Birds, mammals and even box turtles continue to spread it.
As a fruit develops, it is surrounded by a protective calyx covered in hairs that exude tiny drops of sticky fluid. Some observers have suggested that the plant might derive nutrients from insects caught in the sap.
Not so, according to a 2009 study by Sina Pohl at the University of Vienna. She found that the sticky mucilage contains no digestive enzymes; surrounding tissues are unable to absorb nutrients; and protein-storage tissues are absent. Also, unlike carnivorous plants, which tend to grow in nitrogen-poor soils, wineberry grows in nurient-rich soil, so there's no need for any insect supplements.
Sources: University of Vienna; National Park Service
July 6, 2010
The hottest month is getting hotter
After the warmest spring on record, Washington area residents can hope to relax and enjoy what climate scientists are predicting to be a "normal" July. The future, however, is looking toasty.
Washington's average monthly temperatures
Earth's average surface temperature has risen by at least 1.37 degrees since the late 1800s. Climate researchers now expect a further 6.3-degree increase by the end of this century.
Washington's average July temperature
The official temperature for Washington has been measured at varying sites over the years (Reagan National Airport is the current location), so the data shown below can't be used to gauge large-scale climate change, cautions NOAA's Rachel Wilhelm, but "on average, July appears to be getting warmer in the D.C. area."
Sources: National Oceanic and Atmospheric Administration; staff reports
July 13, 2010
Green foxtail provides reward for neglect
In July, green foxtail flower heads are prominent in unmowed lawns and weedy flowerbeds.
If it's too hot to work in the yard or you simply have more pressing concerns, you can still spare a brief moment to taste the fruits of summer indolence. Collect the treat by grabbing onto a foxtail flower and giving it a pull. The flower stalk will squeak out of its sheath, exposing a sweet, succulent tip on which to chew.
Join the crowd
The grass is native to Eurasia, growing best in disturbed areas. It's popular with wildlife. Seeds are eaten by sparrows, doves, blackbirds and mallards. House mice like them, too. Stink bugs and aphids suck the sweet juices. Least skipper caterpillars, flea beetles and grasshoppers eat the leaves.
July 20, 2010
Katydids use wings to sing
As July's heat reaches its peak, katydids add their voices to summer's insect chorus.
Katydid nymphs are shedding their final skins to emerge as adults. Early this spring, they hatched from long, pointed eggs that their mothers glued to crevices in tree bark last summer.
At night, adult males cry out from the crowns of deciduous trees: "Katy did, Katy didn't!" The raspy sounds are produced when the insect raises
its leathery forewings and rubs them together.
Similar to a guitar pick stroking a tiny washboard, the hard edge of the right wing scrapes a ribbed "file" on the underside of the left wing. A special area on the right wing resonates to amplify the sound.
With eardrums on their front legs, females listen to the mating serenade, and each softly answers "tick" to the male of her choice.
Most katydids will never use their wings for flight, but if disturbed they will weakly flutter to the ground. They then start a long climb up to the top of the nearest tree, where they will remain until they are killed, either by a predator or by the first heavy frost.
Listen to a katydid call.
July 27, 2010
The brown rat
D.C.'s second-most-successful mammal
Summer provides an abundance of food and vegetation that supports a seasonally swelling population of brown rats.
"Spring and summer are the peak breeding seasons," says D.C. Department of Health spokeswoman Dena Iverson. "Winter acts as a natural exterminator: When it's cold, rats become stressed and breeding is reduced."
Unless they're held in captivity, rats live only about a year, so they reproduce early and often.
A rat born in May could already be raising a litter of her own by July. It's possible that she was impregnated again only 10 hours after giving birth and could be expecting another 10 pups before August.
District residents can help curb the rat population by securing garbage, taking uneaten pet food back indoors, clearing the yard of weeds and junk, and restricting rat access to buildings by plugging up any hole larger than the circumference of a quarter. Rats love seeds, so your bird feeder may be attracting more than just doves, sparrows and cardinals.
For help with rodent control, dial the Citywide Call Center at 311.
An omnivorous rodent
In addition to dining on human refuse, rats will eat birds, mice, amphibians, small reptiles, fish, eggs, carrion, pet feces, insects, mollusks, worms, leaves, roots, tubers, wood, bark, stems, seeds, nuts, grains, fruits, nectar, flowers, sap and fungi. If poisoned, rats will swallow clay, which absorbs toxins.
Map by Mary Kate Cannistra/The Washington Post
August 3, 2010
Poison ivy's toxic mnemonics
While most people who work and play outdoors recognize poison ivy, they often use a variety of colorful rhymes to to help others remember what the plant looks like.
"Leaves of three, let it be"
Waxy green compound leaves have three leaflets. Brushing up against them can cause the release of a lacquer-like substance called urushiol, which can create an allergic reaction on human skin: redness, itching, blisters.
"Berries of white, run in fright"
As summer unfolds, the round, green fruits of poison ivy slowly enlarge. By autumn, they will turn ripe and white -- and be just as noxious to people as the rest of the plant.
"Hairy rope, dont' be a dope"
Poison ivy exhibits several growing habits: It thrives as a ground cover from woodlands to beach dunes; it can grow into a robust bush; when it climbs trees, the woody vine, covered with wiry reddish-brown hairs, swells in diameter and sprouts arching, tree-like branches. Burning a poison ivy vine is a bad idea: Urushiol is carried in the smoke. If inhaled, it can create a life-threatening reaction in the lungs.
Global warming, poison ivy swarming
Scientists grew identical sets of poison ivy plants in atmospheres with various concentrations of carbon dioxide, based on levels from the mid-20th century, the present day and a projected future. Two-inch rhizome segments were sprouted and cultivated for 250 days before leaves were harvested and measured.
August 10, 2010
More birds, more flights, more strikes
Aircraft collisions with birds reach a yearly peak in August.
A summer's worth of breeding has swollen bird populations, with many of them gathering in flocks that increase hazards for pilots.
"There are at least twice as many birds in the population as in June," says Richard Dolbeer, a science adviser to the USDA Wildlife Services Program. "Recently fledged birds are inexperienced flyers and foragers . . . and are more likely to be struck by aircraft than the more experienced adults."
In the past 20 years, populations of large birds such as pelicans, eagles and geese have been steadily increasing, which has led to many more reported collisions with an ever-expanding fleet of airliners. Since 1990, 24 people have died in 10 such strikes in North America.
Airliners have become more vulnerable to the effects of colliding with birds. The more engines an airliner has, the less likely it is to be brought down by striking a flock. In the past two decades, two-engine aircraft have all but replaced three- and four-engine jets.
In January 2009, a US Airways flight departing New York's La Guardia Airport narrowly averted disaster when the Airbus 320's two engines failed after thrusting through a flock of Canada geese. Pilot C.B. "Sully" Sullenberger managed to land in the Hudson River; all aboard were rescued before the jet sank.
In the past 20 years, more than 1,200 Canada geese have been been hit by civil aircraft.
The abundance of nonmigratory giant Canada geese (a nine-pound jumbo subspecies) has mushroomed fourfold since 1990. Unlike their smaller migratory cousins, these geese generally stay put year-round, creating constant jeopardy for air traffic.
The USDA's Airport Wildlife Hazards Program assists with several methods for reducing goose hazards:
- Egg addling involves coating goose eggs with corn oil, which prevents respiration, halting embryo development.
- Harassment with pyrotechnic devices and other methods. The technique may drive the birds a few miles away, but they tend to return.
- Habitat alteration converts areas surrounding the airport into less- desirable goose territory. Access to water is blocked; grass that is unattractive to geese is planted and mowed to discourage both grazing and nesting.
- Depredation: Geese are shot or rounded up and gassed with carbon dioxide. If a poultry processing plant is available, the carcasses may be donated to a food bank; if not, they're either studied by scientists or buried.
Sources: Michael J. Begier, national coordinator, Airport Wildlife Hazards Program; FAA; USDA
August 17, 2010
Queen Anne's lace
A common weedy flower in sunny, mid-summer ditches.
August 24, 2010
White oak acorns are dropping
August 31, 2010
Goldenrod and ragweed
The back-to-school weeds
In late summer, school-bus-colored flowers appear.
The bright yellow blooms of goldenrod are hard to miss. Their vivid display corresponds with a return to the classroom and with an uptick in allergy symptoms that are commonly blamed on the flower's pollen.
But pollen from goldenrod is rarely carried by breezes. It's sticky and clings to insects, which transport it from flower to flower.
A real culprit for outdoor allergies this time of year is ragweed, which releases an airborne pollen that is a notoriously powerful allergen. Ragweed's green and inconspicuous flowers are much less noticeable than those of goldenrod, which blooms at the same time.
Grains of goldenrod pollen, left, and ragweed pollen, right, are both about 20 microns (or 4/5,000 inch) in diameter and have a similar geometry, but they employ very different strategies for dispersal.
Sources: University of Missouri, Boston Medical and Surgical Journal
September 7, 2010
Homebody house sparrows
By September, house sparrows have ceased breeding and are congregating in small flocks, feeding and roosting together.
Bands of juvenile birds began forming months ago after leaving the nest. They spent a few days with their father, then became independent enough to find grain, weed seeds and invertebrates on their own.
The adults, which choose one mate for the season, soon went back to breeding, raising as many as four clutches before the end of summer. Each clutch holds about five eggs.
Though juveniles may stray short distances, house sparrows are nonmigratory, stay in human-modified areas (such as cities and farms) and stick close to where they were born. Males may even choose nesting sites in the autumn, use the site for a winter roost and convert it to a nest in the spring.
The birds have been in North America since the 1850s, when 50 breeding pairs were introduced from Europe. By 1943, 150 million house sparrows had colonized the country, coast to coast.
The American landscape of the late 1800s encouraged the spread of the house sparrow. The country was dotted with small farms that supplied the cereal grains and livestock fly larvae on which the birds thrive.
Since the 1950s, pesticides have reduced insect numbers, livestock is less spread out, and grain harvest and storage is more efficient, all contibuting to an overall decline in the house sparrow population, which is falling at a rate of about 2.6 percent every year.*
Sources: Cornell Laboratory of Ornithology; "Biology of the Ubiquitous House Sparrow: from Genes to Populations," by Ted. R. Anderson.
September 14, 2010
The mean season
During the summer, waters in the Atlantic Ocean accumulate heat, which fuels a flurry of hurricanes at season's end. Most hurricanes reaching the Washington region do so after being downgraded to tropical storms. Notable exceptions were Isabel (2003), Floyd(1999) and Gloria (1985).
Source: NOAA | Map by M.K. Cannistra/The Washington Post
September 21, 2010
Yellow jacket delirium
As the nest's social structure dissolves with the onset of autumn, unemployed yellow jacket workers behave erratically, increasing people's risk of stings.
The subterranean colony began last spring with a queen emerging from hibernation. In an abandoned rodent burrow, she built a small paper nest of about 40 cells, each hosting an egg. After a week the eggs hatched, and for 12 days the larvae were fed masticated meat and insects by their queen. After 12 days of pupating, mature workers emerged and assumed all labor so that the queen could focus only on laying eggs.
Over the summer the nest grew to as many as 5,000 workers.
Workers and larvae developed a special relationship. As workers fed chewed-up insects -- many of which are agricultural pests -- into the mouths of larvae, the larvae reciprocated with drops of sweet liquid from their salivary glands, an addictive incentive for the workers to return with more food.
As summer winds down, the queen has stopped producing workers and deposits only queen and drone eggs. When they emerge, the two sexes mate, the drones die and the fertile queens eventually seek an overwintering spot in leaf litter or under the bark of a rotting log.
Meanwhile, thousands of aggressive yellow jacket workers are out of a job and wandering aimlessly, their sweet tooth targeted at oozing fruit and sugary soda cans.
Sources: University of Florida Institute of Food and Agricultural Sciences, University of Michigan Museum of Zoology, Journal of Family Practice, Houston Audubon Society