There are more than a thousand species of sweat bees in North America, all of which provide essential services as pollinators.
A Fondness for Beetles and Bees
Of all the predatory insects that live in croplands, none are more successful—or more important in controlling pests—than the legions of beetles. To date, more than 350,000 species of these armor-winged insects have been identified in various parts of the world, making them the largest and most diverse order of living animals. (Asked what he had learned about the Creator from a lifetime spent studying His works, the Scottish biologist J.B.S. Haldane is said to have quipped, “He seems to have an inordinate fondness for beetles.”) By and large, the species found in farmland belong to the family Carabidae, or ground beetles, a group that includes some 40,000 species worldwide. Of these, an astonishing 2,500 species are known to occur in Canada and the United States: that’s 2,500 subtly different ground beetles. The most familiar of their number, the sidewalk beetle, is a European species that was accidentally imported by early settlers and that, ever since, has been fast-footing it through lawns and gardens across the continent. Most of the native carabids are variations on the same theme: small, black, shiny, and intensely busy.
In their adult form, Nuttall’s blister beetles are as showy as the flowers on which they feed.
Although the majority of carabid species cannot cope with frequent disturbance and are not found on cultivated plots, the number of species that have made the transition to farmland is impressive. For instance, by the simple expedient of setting wide-mouthed jars into the soil and fitting them with funnels instead of lids, a researcher in South Dakota was able to trap 127 kinds of ground beetles on farmers’ fields. And while many of these species were rarities, several were exceedingly abundant, with peak, late-summer populations of 4,000 to 6,000 beetles per acre, or 10,000 to 15,000 per hectare. On one extraordinary occasion (when a heavy rain a few days earlier had moistened the soil and created what must have been ideal conditions), one species of tiny carabid topped the charts at an estimated density of 5.6 million individuals per acre (13.8 million per hectare). No matter how you put it, that’s a lot of beetles. Yet for the most part, we don’t even know they’re out there because they hide from the sun by day (in the soil or under litter and leaves) and only come out to hunt in the cool, moist air of evening.
Sidewalk beetle
But under cover of darkness, what carnage! Although a few species of ground beetles feed on plants, most are voracious predators that prowl through the dark, searching for insect eggs, larvae, pupae, and soft-bodied adult forms. While some carabids are thought to be specialists, with their sensory radar tuned to specific prey, others appear to be opportunists that eagerly accept any insect food that comes within reach of their mandibles. As a result, they consume untold quantities of insects that might otherwise damage crops, including wireworms, cutworms, caterpillars, maggots, and aphids, among many others. It would not be overstating the case to say that farmers could not attain profitable yields without the unpaid—and generally unheeded—exertions of ground beetles.
The best way to safeguard the diversity and abundance of these essential “farm animals” is to conserve their habitats. Practically speaking, this means maintaining weedy field margins, grassy watercourses, irrigation ditches, roadsides, fence lines, shelterbelts, pastures, wetlands, and other semiwild refuges where the land is subjected to minimal disturbance. Such areas not only provide safe havens during insecticide application—beetles have been seen running toward field edges to flee from toxic sprays—but also serve as sheltered daytime hideaways. (Dense tangles of vegetation offer humidity and shade.) Perhaps most important, these undisturbed patches also provide essential wintering habitat, where beetles can burrow down into the ground and wait for spring’s return. The overburden of vegetation provides protection against extreme cold and may also trap an insulating layer of snow, thereby further improving the insects’ chances of survival. In one experiment, a raised, grassy berm, or “beetle bank,” was found to shelter 100 overwintering carabids in every square foot (1,100 per square meter).
Retaining strips and patches of undisturbed land is the minimal precondition for sustaining the web of life in intensively farmed regions. Although it is true that these small, untended corners can harbor weeds and insect pests, any problems are generally far outweighed by the benefits. Given that the vast majority of native species are either beneficial or neutral to farming, reserving space for them becomes a simple matter of economic and ecological good judgment. Besides pest control, there is the additional plus of free pollination services. Although crops like wheat and corn are pollinated gratis by the wind, many others—including sunflowers, canola/rapeseed, lentils, alfalfa, and peas— must be pollinated by insects, most notably, by bees. Unlike the colonial honey bee (another import from Europe), most of the thousands of species of native bees are solitary nesters. Each female lays her eggs either in holes in wood or, more often, in cells in undisturbed ground, provisioning each with a dollop of a pollen-based mixture. In producing this “bee bread,” the female trails pollen from one flower to the next, thereby ensuring that the plants set seed and produce a marketable yield. Thus, simply by conserving areas of semiwild habitat where bees and other wildlife can live, farm people can expect to profit in every sense of the word.
Farming and Birds
If the introduction of intensive agriculture constituted a revolution in the ecology of the Great Plains, prairie farming itself has since undergone radical change. A lot has happened since the horse-and-buggy days. The original patchwork of small, diversified homesteads, with a family on every farm, has gradually been transformed into a sparsely populated landscape of large-scale, specialized operations. Where once there were fields of oats for the draft horses and pastures for the family cow, there are now entire sections devoted exclusively to the production of cash crops. Bigger machinery has called for bigger fields, with clean straightaways and right-angle turns; it’s hard to steer something as big as a bus around the land’s natural contours. Squeezed between high costs for fuel and other necessities and ruinously low prices for what they grow, farmers increasingly rely on government income-support programs. Because their entitlements are typically based on acreage under cultivation, they have been pushed to work every square inch of land and to view natural areas as “idle” and “unproductive.”
No one knows, in any detail, how these successive changes in the agricultural landscape have affected populations of beneficial insects on prairie farms (though a sharp decline in many species of native pollinators is cause for alarm). Fortunately, however, researchers have been more successful in tracking the fortunes of farmland birds. The greater prairie chicken, for example, was originally a bird of the tall-grass prairie and the neighboring prairie-and-oak savannas. As agriculture spread, this handsome brown-and-buff-barred grouse expanded its range widely, advancing west to the foothills of the Rockies, south to the Gulf of Mexico, and north to the Aspen Parklands. When agriculture was in its frontier phase, this whole broad sweep of country catered to the chickens’ needs, combining grasslands for cover with grain fields for foraging. Soon there were more prairie chickens on the Great Plains than there had ever been before. For example, the Omaha Republican reported that, on September 6, 1865, two hunting parties led by Captains Kennedy and Hoagland bagged a total of 708 prairie chickens (together with 6 quail, 10 snipe, 14 hawks, 16 ducks, and 2 rabbits). Such one-day totals were not uncommon.
Horned lark
Kildeer on nest
Although protective laws were quickly invoked, enforcement was lax and the population of prairie chickens inevitably began to pay the price. Yet even after the slaughter ended, sometime around World War i, prairie-chicken numbers did not rebound. By then, the look of the country had shifted from a semi-natural landscape, with small patches of cultivation—perfect prairie chicken habitat—to an intensively farmed ecosystem with small remnants of grassland. The result h
as been the slow and painful disappearance of the species from four Canadian provinces and eight American states, along with the fragmentation and contraction of the birds’ remaining range. Several key populations continue to diminish.
The point here is not just the plight of the greater prairie chicken, as compelling as that is. It is the ongoing narrative of cause and effect, as farming evolves from one stage to the next. Every modification of agricultural practices produces ecological consequences, destroying habitat for some species and, with luck, creating it for others. Thus, the very changes that spelled doom for prairie chickens were to the advantage of other birds, which flocked in to take advantage of novel habitats, including shelterbelts, road allowances, and field margins. Today, several decades further into the story, these strip habitats in their turn have begun to disappear, as farmers strive to push production to the limits. Since the 1930s, it is estimated that between 30 and 80 percent of the field margins in the central United States have been brought under the plow, and the same trend can be seen across the Great Plains in general.
The consequences of these changes are not difficult to foresee. A study conducted in the farm country of north-central Iowa found that the region was home to a fabulous diversity of breeding birds, with close to one hundred species in total. Of these, almost half nested in woody fencerows and windbreaks, a quarter in wetlands and sloughs, and another half dozen or so in hay fields. Removing any of these elements from the landscape removes its resident birds. By the time only the crops and weedy strip habitats are left, only eighteen species remain. And without the weedy margins, there are just three survivors: the vesper sparrow, the horned lark, and the killdeer. (Because these species are adapted to nest on bare or sparsely vegetated prairie and to breed early in the season, often before field work begins, they can succeed right out in the crops where few other breeding birds venture.)
Abandoned farmsteads not only provide daytime roosts for great horned owls, they also provide shelter for rodents, foxes, and bats, among many others.
The more the agricultural landscape is simplified, the fewer species of birds it can support. It’s not exactly rocket science. Among the common farmland birds that are now declining in parts of the Great Plains are such stalwarts as American crows, European starlings, house sparrows, mourning doves, common grackles, and American goldfinches.
At the same time, happily, some recent trends in agriculture appear to be more positive for our feathered friends. One is the widespread adoption of no-till and minimum-till farming methods. Rather than cultivate the land—leaving the soil bare and exposed—the gospel of no-till asserts that the ground must always be covered by vegetation. To this end, stubble and other crop residues are left in place after harvest for direct seeding the following spring, and herbicide spraying, instead of tillage, is used to control weeds. Designed primarily to prevent soil erosion, this technique has also turned out to provide nesting cover for certain species of ground-nesting birds, including meadowlarks, pheasants, and grasshopper sparrows. (To return to Iowa again as an example, no-till cornfields in that state have been found to provide nesting sites for a dozen species of birds—up from the expected three—and the nests are packed in at many times the usual density. In this respect, no-till achieves the same benefits as organic farming.)
There is always the worry, however, that these lively no-till fields may ultimately function as ecological traps, first attracting birds in large numbers and then subjecting them to seeding, spraying, and other nest-wrecking disturbances. Just because a species is present doesn’t mean that it is managing to reproduce. What’s more, if the new soil-holding techniques enable producers to cultivate steep slopes and rough country that could not be farmed in the past, then no-till may be responsible for a net loss of quality habitat.
Fortunately, these ambiguities do not cloud the promise of another tactic: the removal of marginal farmlands from crop production. This process began in earnest during the Dirty Thirties, when many of the dustiest lands in the Dust Bowl were brought under public management as National Grasslands in the United States and as pfra (Prairie Farm Rehabilitation Administration) community pastures in Canada. Thereafter, progress was sporadic, with periods of reversal, a continuing loss of native grassland, and a gradual extension of the acreage under cultivation. In 1985, however, the cause of biodiversity received an unintended boost when the United States introduced the Conservation Reserve Program (crp). By contracting with farmers to put marginal farmlands into permanent cover (usually either introduced or native grasses) for a specified term, government officials hoped to protect the soil from erosion and simultaneously put some cash into the pockets of farmers who had been hit by the collapse of world markets. As good luck would have it, the program also ended up offering a helping hand to another group of hard-pressed prairie residents. Grassland birds that for decades had been losing ground—fading away year by year—found refuge in the 30-plus million acres (over 12 million hectares) that were protected from cultivation. Alas, the government giveth and the government taketh away, and these gains are not secure.
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> FLIGHT OF THE BUMBLEBEES
Bumblebees are the teddy bears of the insect world, fat, fuzzy, cute-as-bugs, and surprisingly docile. Although they are equipped with stingers, they seem reluctant to use them unless their nests are seriously threatened. Of all the native species of North American bees, the fifty-odd species of bumblebees are the only ones that are social rather than solitary.
Instead of operating as single mothers that provision young on their own, bumblebee queens are assisted by a busy, buzzy work force of helpers. The story begins in the spring when the queen (the only member of the colony to overwinter) emerges from her tiny underground cell and sets out to find a suitable site for her nest. Once she has found what she is looking for—typically a clump of fine vegetation on the ground, in a building, or down a rodent hole—she fashions the nesting material into a ball, within which she deposits both a little wax pot of honey and a lump of pollen-and-honey mixture. The queen feeds from the honey pot and lays her eggs (all female) on the pollen lump, before covering them with wax and incubating them. After about five days, the larvae hatch, feed on the pollen, and begin the month-long transition into adult workers. By the time the first batch is ready for action, the queen has laid a second brood, which the workers then help to rear. And so it goes, for the rest of the summer. Toward the end of the season, when the colony reaches its peak, the queen produces a brood of male and female larvae that, royally provisioned by the workers, grow up to be breeding males and virgin queens. After this sexual generation leaves the nest to mate, the entire colony dies off, except for the young queens, which tuck themselves underground to wait for spring.
Sometimes, however, this simple story line takes a strange twist, and the reproductive bees that fly out from the nest are aliens. In addition to social bumblebees, there are also parasitic forms that require workers to tend their larvae but that cannot produce their own helpers. Instead, a parasitic bumblebee queen enters an active colony, ousts the reigning monarch, and coopts the worker bees, which henceforth help to tend the larvae and pupae of the invading species.
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> FAT OF THE LAND
Until the early 1940s, lesser snow geese made a leisurely passage up the Missouri Valley in spring from wintering grounds on the Gulf Coast to nesting sites in the Arctic, pausing to feed in shallows and marshes along their route. On the return trip in fall, however, most of the population made the journey more-or-less nonstop and were seldom seen along the river. All that began to change in the 1950s, when flurries of snow geese began showing up along the Missouri in both spring and fall, in ever-increasing numbers.
This change appears to have been precipitated not by natural causes but by a shift in farming techniques. Until the 1950s, most of the corn grown on the Great Plains had been harvested by hand, a method that was laborious but thorough. The newfangled mechanical pickers and combines,
by contrast, were quick-and-dirty machines that left large areas of the countryside strewn with top-quality goose feed. Thus, the table was set for snow geese (and other waterfowl), which shifted out of the wetlands to gorge on the spilled corn. Thanks to this superabundance, more snow geese survived and went on to produce large broods of equally well-nourished youngsters.
As irrigation allowed corn production to expand, the geese expanded, too, eventually shifting their principal spring migration westward toward central Nebraska. Each spring, not just flurries but blizzards of snow geese spill into the wetlands of the Rainwater Basin and Platte River Valley, where they build up stores of fat and protein before continuing on their journey. Recent research suggests, however, that the geese are not faring as well as they used to, perhaps because of a shortage of food; the efficiency of the corn harvest has been greatly improved. Concern has also been voiced about the shift from corn to soybeans—poor provender for geese—and the introduction of genetically modified varieties. Since genetically modified soybeans are immune to herbicides, they can be sprayed for millet and other weeds, thereby removing an important alternate source of food not only for migrating geese but also for other seed-eating birds and rodents.
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LONG-RANGE
FORECAST
For a long time it has come back to us in wishes, this great prairie and these beautiful canyons.
Prairie Page 25
