Posted 8/25/15 (Tue)
By John D. Taylor
You’ll see them flittering, white or pale yellow wings flashing, on a warm afternoon, along roadsides or floating across your backyard by the dozens. Later, they appear as a pair of wings and yellow goo, squashed into the grill of your car.
They are butterflies -- specifically white and yellow-colored cabbage, clouded sulphur, checkered white or alfalfa butterflies -- according to information from North Dakota State University (NDSU) and Divide County Extension Agent Keith Brown.
Brown said these butterflies belong to a group of 14 species collectively known as the whites and sulphurs.
The alfalfa butterfly is a North American native. Before the introduction of alfalfa this butterfly fed on native legumes. Now, however, abundant alfalfa and clover fields provide habitat.
The white-winged cabbage butterfly – males have one dark wing spot, females two – is not native to North America. A European species, it entered Canada during the 19th century and spread across the continent, displacing some native species in the process.
The North Dakota Agricultural College Experiment Station talked about cabbage butterflies being a problem as early as 1891, and recommended 180 degree water or a 1:4 mix of pyrethrum and flour to dust plants.
From a distance, clouded sulphur and alfalfa butterflies look quite like cabbage butterflies. However the clouded sulphur and alfalfa butterflies are often the variety seen along roadsides, around blooming alfalfa and clover patches.
“The reason you see so many butterflies in roadside ditches,” Brown said, “is because the alfalfa is blooming and they are attracted to blooming plants.”
White and sulphur butterflies are quite attracted to members of the brassica plant family, which includes vegetables like cabbage, broccoli, cauliflower, Brussels sprouts, canola and mustard greens, as well as a number of wild plants and escapees from cultivation.
Butterflies lay eggs that grow into larvae – caterpillars – the young of these insects. The larvae, deemed “eating machines” by NDSU entomologists, feed on both crops and wild prairie plants.
Cabbage butterfly larvae, for example, get their name from their fondness for cabbage. The larvae are found on the underside of cabbage leaves, Brown said, and in high concentrations, can chew holes through the leaves, which can stunt plant growth.
However, only the larvae cause damage and in most cases this is minor, mostly affecting home gardeners.
“No one calls about this being a problem,” he said. “The main concern is eggs, and worms. Watch garden plots.”
Commercially-raised crops like canola, are seldom damaged by these butterflies because by the time butterfly populations peak – late summer – canola plants are usually mature, ready for harvest, he said.
Adult butterflies sip nectar and eat pollen from plant flowers and can actually help pollinate plants, so they are more benefit than problem, especially when honeybees and other pollinators are absent.
Cabbage and alfalfa butterflies are the most common species locally, Brown said.
Some of the 14 species of white and sulphur butterflies spend the winter here, he explained, some are blown in from other locales on favorable wind currents.
Butterflies typically create several generations of offspring over the summer months, so their numbers compound, leading to high end-of-summer numbers.
“Butterfly populations build all summer to reach a point where some years they are everywhere, like this year,” Brown said, “some years there are not so many.”
As part of the life cycle of butterflies, when the caterpillar matures enough, it will morph into a chrysalis (or pupa), a case-like structure surrounding the larva where the caterpillar undergoes physical changes to grow wings and legs.
When the adult butterfly emerges from this casing, it flies away to reproduce, beginning the cycle again.