This is the time of year when caterpillars make their appearance in some of your flowers and vegetable plants, especially cabbage types that include cabbage, broccoli and cauliflower. Many blooming annuals and perennials also come down with a bad case of caterpillars during the late summer months, too. It is important to rid your gardens of these pests as they will eat and grow ten thousand times their weight in less than 20 days!
During the early stages, they hide from light and eat mainly at night making it difficult to realize what is happening to your plants. Later in life as they quickly grow, they are totally different in their habits. Now they boldly eat during the day while you can see them. Treatments of Bt, or DiPel, (aka; Bacillus thuringiensis) is an organic insecticide which effectively helps to eliminate caterpillars and any other worms that may be present. Bt is usually applied as a dust but may be mixed in water and sprayed onto the plants. After the water evaporates, the dust remains.
Some caterpillars have fine hairs with sharp barbs that can actually be harmful to humans. Normally a skin rash is the most common problem but fatalities have been reported in Brazil.