Are you growing any cole crops, such as cabbage, broccoli, kale, radish, or turnip, in your garden? If you are, it's a good idea to check them out for imported cabbageworms. As an adult, imported cabbageworms are pretty white butterflies. As a caterpillar these larvae are light green with thin yellow stripes running down their body; a series of short hairs gives it a velvety appearance. It's the caterpillar stage that damages plants by chewing holes in the leaves, sometimes seriously defoliating them.
These crops can tolerate some feeding. However young seedlings and transplants are particularly susceptible to feeding injury and should be protected. Checking plants regularly is very important so any infestations can be spotted quickly to minimize injury. If any imported cabbageworms (and cabbage loopers later in the summer) are discovered, there are several options for dealing with them, including handpicking and using the low impact insecticide Bacillus thuringiensis. For more information, see Caterpillar pests of cole crops in home gardens.