Answer: Based on your description, it's impossible to tell if the caterpillars are causing a problem or not. Normally, caterpillars damage a plant by eating the foliage. If this is happenening, you might try to hand pick them or you might use Bt (Bacillus thuringiensis) according to the label instructions. If you use the Bt, keep in mind that the caterpillars eat a leaf with Bt on it, stop feeding, and then die several days later.
Your imptiens might be wilting for a number of reasons, but the most common is lack of water. They
grow best in rich, moist soil in filtered or partial shade. The brighter the location the more water they need. If they are grown in pots or under trees in competition with tree roots, they need extra water. As the summer weather heats up, they also need more water. Since they have succulent stems, they will wilt when thirsty, but in my experience they may also wilt late in the afternoon on very hot days but perk up again as soon as it cools off for the night. If your impatiens are wilted in the morning, or if the soil around them is dry it is time to water!
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