Pollinators: Pieris

A flock of cabbage butterflies

(Pieris rapae)

If you see a pretty white butterfly, more likely than not you are seeing an invasive species that was accidentally introduced to this country and to many other parts of the world more than a century ago.

The cabbage white butterfly is noticeable, pretty and soft, it visits gardens, meadows, you name it. Perhaps the only places beyond its reach are higher elevations. It starts flying early in the season and produces several generations throughout the summer and fall. No wonder it is seen so often.

Cabbage butterfly

(Pieris rapae)

The name refers to the plant its caterpillar feeds on, cabbage. It also eats other members of the mustard family, such as cauliflower and kale and it is regarded as a serious pest. It also feeds on a number of wild, non cultivated mustards, including the invasive garlic mustard.

The cabbage butterfly is related to a group of native butterflies, the so called whites, yellows and sulphurs or family Pieridae. Their colors, as the names indicate are either whites or yellows. The caterpillars of most of them also feed on plants of the mustard family. A total of 58 species lived in North America before the arrival of this newcomer. Nowadays, the cabbage white is seen as often as all of them combined. One wonders if the growing numbers of this invader are having an impact on the populations of native Pieridae butterflies.

Orange sulphur butterfly

(Colias)

In summary, it has the qualities of so called weedy species, with high rates of reproduction, very adaptable to different food sources and a variety of habitats.

Virginia white butterfly

Pieris virginiensis

The cabbage butterfly reminds me of several insect species that were brought to this country intentionally or accidentally and proceeded to become incredibly widespread in a relatively short time. Now, some of them are more abundant than any of their native relatives. Here are a few examples: the Asian ladybug, the Chinese mantis, the giant resin bee, the European paper wasp, the drone fly, and the brown marmorated stink bug.

David Quammen, a distinguished journalist who has written extensively on conservation and ecology, has coined the term “Planet of Weeds,” meaning that the ecological changes caused by humans are having a severe impact on the flora and fauna of the entire planet. We had transported unprecedented numbers of species of plants, animals and bacteria beyond their natural distributions with the consequence that many of them have become established in their new surroundings. Not only do they become established but spread out from the original place of introduction, thus deserving the name of invasive species. They impact the local flora and fauna, bringing up the extinction of many species. In this way we are causing a mass extinction, comparable to some of the most serious mass extinctions of the past.

Specialist species are more vulnerable to extinction. The ones that have the best chance for survival are the weedy ones, the adaptable generalists. We are creating an impoverished world, gradually losing precious biological diversity, biodiversity for short. It may take millions of years for this biodiversity to raise back to the present levels. The human species may never see that.