Life on asphalt

Flora and fauna of the world’s roads

Around the world, some 36 million kilometers of paved roadways carry over one billion vehicles. But some animals, plants and organisms are undaunted by the traffic and unfriendly environment.

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In the lore of the Native Americans, the coyote (canis latrans) is presented as agile, wily and adaptable. Also known as the prairie wolf because it originally populated the dry prairies of the southwestern states, the coyote's skillset has enabled the species to migrate into urban areas where they have no natural enemies and more accessible food sources. For decades they have been establishing colonies in the majority of American cities. The medium-sized canines have sprawling territories, and roads are often the most convenient way to patrol them. In Chicago, San Francisco and Ottawa, drivers regularly observe coyotes waiting for stoplights to turn green, or looking over their shoulders for approaching traffic at crossroads. In Los Angeles they even manage to cross the ten lanes of Highway 101 – unlike bobcats and mountain lions, whose habitats are often severely constrained by busy roads.

The narrow-leaved ragwort (senecio inaequidens) is an exceptionally adaptable, owering plant with eye-catching golden blossoms. Originally from southern Africa, it was imported to Europe and successfully adjusted to the seasons in the northern hemisphere. What is more, it can cope with dryness and heat, as well as with the salt used to keep roads from freezing. Every year since the mid-1970s, tires and the air ow from passing vehicles have spread its seeds a few kilometers further. The hard shoulders of paved roads might not be the most hospitable of habitats, but any species able to survive will nd a large, well-networked territory in which to ourish.

The tetramorium caespitum is one of the most common species of ants in Central Europe. It was introduced into the southern and eastern United States by ships bringing emigrants from the Old World, most likely around 1700. There the species is famous as the pavement ant because it likes to build its nests under sidewalks and engages in spectacular roadside battles with other ant colonies during the spring. Moreover, their taste for "street food" is an important factor in urban waste disposal: ecologists have calculated that the populations between New York's Broadway and West Street polish off an astonishing 60,000 hot dogs, 200,000 cookies and 600,000 potato chips a year. Scientists believe that the ants move faster on warm, dry roads than in natural environments, increasing their energy needs and therefore their appetites.

Bridges and tunnels may be miracles of engineering, but repairing damage can be a nightmare. In future, the sporosarcina pasteurii could become the guardian angel of motorists. Normally the tiny bacterium lives in high-alkaline lakes near volcanoes, where it can survive for up to 200 years without oxygen and food. However, if material scientists combine it with a nutrient solution of nitrogen, phosphorus and calcium lactate, and then blend it into concrete, the resulting mix acquires self-healing properties. As soon as faults appear and allow water to penetrate, the sporosarcina pasteurii goes into action: it consumes the nutrient solution and excretes solid limestone that quickly and reliably repairs cracks of all sizes. And because it also consumes oxygen, the bacterium helps prevent corrosion in reinforced concrete.

American cliff swallows (petrochelidon pyrrhonata) are very fond of building their nests underneath elevated roads and highways. In some colonies there can be more than 2,000 nests attached to the walls in close proximity. The birds have adapted to their modern habitats at lightning pace. They now have much shorter and more rounded wings than thirty years ago. That can be a lifesaver: whereas long, narrow wings are ideal for flying distances at speed, today American cliff swallows can maneuver much more quickly, enabling them to dodge the passing traffic. Vertical takeoffs from the road surface are also easier. While some 80 million birds a year become roadkill in the United States, the new generation of these swallows is far less likely to collide with vehicles and vice versa.

The spring agaric (agaricus bitorquis) a relative of the common button mushroom, is naturally tasty. Unfortunately, it grows in less than hygienic environments, most typically on the roadsides where people walk their dogs. This has earned it the nickname pavement mushroom, not least it can effortlessly push up thick paving stones and pierce asphalt surfaces. To achieve this, it absorbs water from the surrounding soil into its cells until they are full to capacity. The resulting osmotic pressure can reach up to 15 bar. By comparison, a car tire is inflated to around 3 bar and an airplane tire to 14 bar. Later, the 4- to 10-centimeter wide cap of a white mushroom sprouts from the volcanically ejected cone – often to the astonishment of people who happen upon it.

In the lore of the Native Americans, the coyote (canis latrans) is presented as agile, wily and adaptable. Also known as the prairie wolf because it originally populated the dry prairies of the southwestern states, the coyote's skillset has enabled the species to migrate into urban areas where they have no natural enemies and more accessible food sources. For decades they have been establishing colonies in the majority of American cities. The medium-sized canines have sprawling territories, and roads are often the most convenient way to patrol them. In Chicago, San Francisco and Ottawa, drivers regularly observe coyotes waiting for stoplights to turn green, or looking over their shoulders for approaching traffic at crossroads. In Los Angeles they even manage to cross the ten lanes of Highway 101 – unlike bobcats and mountain lions, whose habitats are often severely constrained by busy roads.


Stefanie Hardick, born in 1978, writes about science and historical topics as a freelance journalist in Berlin.

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