Answer: Without seeing them, it's hard to say what they are. It sounds as though either they hatched from the undersides of your plant's leaves, or somehow they spread the word quickly about your Sweet Broom. You can try to remove them by hand, or a common control for caterpillars is Bt (Bacillus thuringiensis). It is available at most garden centers. Bt is in an insecticidal bacterium that you apply when caterpillars are small. When used as recommended, it is not harmful to pets, people or the environment. Bt contains spores of a lethal bacteria that germinate in the gut of a caterpillar after ingestion and causes them to stop feeding-and eventually kills them. If you leave the caterpillars alone, they will turn into butterflies or moths. If you decide to leave them alone, let's hope you have some lovely butterflies or moths in the coming weeks to make up for the loss of the leaves on your plant.
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