Since I filed my last column, I’ve crossed the Atlantic and spent 10 days in Kent, England (coincidentally the point of origin of many of the Vineyard’s first European settlers). As always, I found being in a new place exhilarating, and cultivating an acquaintance with the local wildlife took up a good portion of my time.
Lots of what I saw, of course, was unfamiliar. On a different continent, separated from North America for millions of years as the Atlantic gradually widened, Europe features the results of different strands of evolution. And in its fundamental ecology, the area I was visiting differed dramatically from the Vineyard (the bedrock, for example, was mostly chalk, with profound implications for soil chemistry, drainage, and land use history).
While I reveled in being on the “steep part of the learning curve,” figuring out new species at a lively clip, I was also taken aback by how much was familiar, either the same species I know from the Vineyard, or relatives so close as to be hard to distinguish.
For example, the first fly I identified in Kent was Syritta pipiens, a hoverfly about a quarter-inch long and sporting enlarged, bike-racer thighs on its hind legs. Syritta was also the last fly I had noted as we bolted out the door for our outbound ferry: This species, introduced accidentally into the U.S. well over 100 years ago, is now numerous in our region.
In short order, Syritta was joined in the garden at the house we stayed in by the familiar honeybee and another hoverfly, Eristalis tenax. On pasture land, many of the grasses and weedy plants were familiar to my North American eyes. Starlings, rock pigeons, and house sparrows, abundant exotic species on our side of the pond, were likewise numerous in Kent. Buddleia, or butterfly-bush, familiar from gardens on the Vineyard, grew widely on the landscape. This plant, originally from China, is as exotic in England as it is on the Vineyard!
Some of these species were deliberately transported to North America, by humans with varying motivations and often a naïve or old-fashioned understanding of ecology. The house sparrow, for example, was a deliberate import, invited over because of its close association with livestock and stables. House sparrows nest happily under the eaves of barns and outbuildings, and hairs from a horse’s tail rank among their preferred nest-building materials.
From the human perspective, house sparrows are voracious consumers of flies, especially of fly larvae growing in animal dung. They are effective fly-suppression systems, and this useful characteristic led to the importation of these sparrows. Regrettably, it also turned out that house sparrows, which prefer to nest in cavities such as hollow trees, compete very aggressively against native species, like bluebirds, that prefer the same nesting sites.
Many other exotic plants and animals made it here on their own, often in surprisingly short order after Europeans began emigrating to what is now the United States. As seeds, eggs, larvae, or even adults, a wide range of plants and insects hitch-hiked on ships headed for the New World, tucked away in animal forage, plant material, building supplies, or perhaps just in luggage or random goods being transported. Species that found the conditions they needed here simply set up shop.
Some of these accidental or incidental introductions have proven almost as destructive as the house sparrow and the starling. But many more, perhaps the vast majority of introduced species, have had limited ecological impacts in their new home. In many cases, the new arrivals simply blend in as just one more species among a multitude of others, native and introduced alike. Those hoverflies I mentioned seem to fall into this category; they’re common enough, but no more common than some native relatives.
In other cases, an introduced species associates mostly with other introduced species that are of little use to native North American wildlife, limiting the potential for conflict. For instance, the introduced European skipper butterfly (Thymelicus lineola; in England the common name is Essex Skipper) can be astonishingly abundant in meadows and pastures in the northeastern United States.
But its caterpillars feed on similarly exotic grasses, imported by Europeans as part of their pasture mix and of little use at all to our native butterflies, which are not evolved to feed on them. European skippers, it seems, can get as abundant as they want without harming native species, because they occupy a niche that no natives want to occupy.
In short, as the human economy has globalized, so has the entire ecosystem. Effects of this change range from catastrophic to benign to, arguably, positive. But for good or ill, the global movement of humans has also created a distinctive new global ecology.