Two days ago I was asked to take a look at a planting of cabbage. They wanted me to identify the worm and how to control it. Lucky this one was easy. It’s an imported cabbageworm (Pieris rapae) on cabbage. These guys are much easier to kill than some of the worms we deal with in row crops.
The imported cabbageworm occurs in temperate regions around the world, and was first observed in North America in 1860 at Quebec City, Canada. It dispersed rapidly, and by 1886 was found in the Gulf Coast and Rocky Mountain states. It is now widespread in North America although few cabbageworms reportedly survive the winter in most of Canada.
Pieris rapae is easily confused with other common cabbage white butterflies: Pontia protodice, southern cabbageworm; Pieris napi, mustard white; and Ascia monuste (Linnaeus), the southern white. Prior to introduction of the imported cabbageworm, Pieris napi (Linnaeus) was the dominant cabbage butterfly in the north, and Pontia protodice (Boisduval & LeConte) was the principal cabbage-feeding butterfly in the south. Both have been largely replaced by P. rapae, although they sometimes co-occur on cultivated crucifers or on weeds.