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Friday, May 6, 2016

The Most Invasive Butterfly: Cabbage White Butterfly (Pieris rapae)

A flock of cabbage butterflies
(Pieris rapae)
© Beatriz Moisset
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)
© Beatriz Moisset
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)
© Beatriz Moisset
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
© Beatriz Moisset
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.

Drone fly (Eristalis tenax)
One of many introduced, widespread species
© Beatriz Moisset

6 comments:

  1. I find it so odd that the scientific name of a butterfly can be the same as the scientific name of a plant! But thanks for writing about this, I didn't realize one of these guys was non-native.

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    1. The name was chosen intentionally in this case; rapae is derived from rapa, the specific name of the host plant of this butterfly. The same thing happens with the oleander aphid, called Aphis nerii, in reference to the genus name of its favorite host, the oleander plant, Nerium. This is very common. On the other hand, sometimes plants and animals have the same name, just by accident. At Bugguide.net we have been collecting examples of this. You can see them here: Plants v. Animals (ICBN v. ICZN), http://bugguide.net/node/view/443579. Curiously, one example is this very butterfly. Pieris is also a plant in the family Ericaceae. Perhaps you were referring to it. See Wikipedia article: https://en.wikipedia.org/wiki/Pieris_%28plant%29

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    2. Ellen - There are quite a few botanical-zoological genus name homonyms, in fact, and they are permissible under the codes of nomenclature.
      As for the cabbage white I have the impression from watching them a bit that, at least here in Missouri, they prefer to lay eggs on mustards of Eurasian origin, while native whites (checkered whites, and especially orange-tips) utilize mostly native mustards. Still checkered whites have declined in numbers in recent decades, and this may be related to the abundant presence of Pieris rapae. I wonder though, because the introduced butterfly was already quite abundant when I was a child, and it was one of the first butterflies I ever learned, but checkered whites were still quite abundant then, even after multiple decades of coexistence.

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  2. Beatriz, is it unusual in the butterfly world (here in North America) to have an alien invasive? Are there others?

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  3. I know two introduced skippers, Asbolis capucinus (Monk Skipper) (from Cuba) and Thymelicus lineola (European Skipper) (from Europe), and one hairstreak, Electrostrymon angelia (Fulvous Hairstreak) (possibly introduced from the West Indies). There may be more. As for Lepidoptera in general there may be more than 200 introduced species.

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