Windswept_ The Story of Wind and Weather - Marq de Villiers [111]
There is more to life in the lower atmosphere than birds. Much, much more life, a riotous carnival crowd of life . . . The air in the first thousand yards or so off the ground is filled with a dense crowd of wind-blown pollens and fungal spores, as well as myriad insects and the birds that devour them; at some estimates, the air above grasslands in temperate zones can carry almost a million insects, or at least organisms of one kind or another, per square mile at any one time.1
The earliest creatures to learn to use the wind were the plants. Spores and fungi, which are ancient even by plant standards, depend on the winds for their movements and their propagation. All orchids, which are really just host colonies to fungi, still use wind to propagate; in some species a single flower can produce four million seeds, capable of surviving wind-borne trips of up to 1,800 miles. Other stay-at-home blooms, including some orchids, collect their nutrients from afar: I've already remarked on a species of orchid growing in the rain forest canopy of the Amazon that depends on African dust for a large share of its nutrients. And allergenic plants such as dandelion, ragweed, and goldenrod cause outbursts of sniffling in the spring, as their pollen is carried on the winds.
Many large plants use the winds to disperse seeds. Canada's national tree, the maple, spreads its seeds on little winged husks, which will carry long distances in a small breeze. Conifers spread their pollen in the winds. Whole plants, too, use the winds. The tumble-weeds of arid areas are entirely wind-dependent for their travel; one of our coaches at school used to make us chase tumbleweeds across the dusty plains in the Orange Free State, the better to get us fit for the hockey season (well, it beat doing laps).
Winds can bring alien invasions as well as benefits—see those soy-eating fungi invading Arkansas from South America. In Cape Town, one of the windiest places on the planet, agronomists imported the Port Jackson willow from Australia in a vain attempt to anchor the sands of the so-called Cape Flats, which were threatening to blow away and turn Cape Town proper into an island. It spread rapidly in the winds, and is now a threat to native species; my sister is one of thousands of Capetonians who turn out in organized "hacks" to root out this and other aliens. As Jan DeBlieu points out, Hurricane Andrew in 1993 knocked down so many native trees in Florida it helped the spread of four alien imports: melaleuca, Australian pine, Brazilian pepper, and marlberry2
Insects, too, have worked out dozens of ways of using the winds. Some of them do it by simply getting aloft and being blown along. In 2004, locusts invaded Egypt again, just as they did in biblical times, using the prevailing winds to do so. Many otherwise wingless insects do the same. At sea, certain microorganisms are thrown into the air by wave action, and are carried enormous distances on the winds in aerosols.
Other insects have learned to use wind in more indirect ways. That spiders can employ wind to cross fairly long distances between trees, dangling themselves on the end of a long rope of silk, is commonplace, and can be seen in pretty well any backyard. But entomologists have also identified some species of spiders that can build simple sails from their silk to lift themselves into the air. To some degree they can control their flight by lengthening or shortening the threads they produce.3
II
One autumn morning, after yet another gale had