The Gypsy Moth Caterpillar Infestation: Some Answers: No, they won’t kill the trees, some denuded trees may even releaf this year. Yes, they are cyclical—about every 10 to 15 years—but this one is strange, out of sequence, and heavy. No, there’s not much you can do about it now. Yes, they are likely to return next year, so be prepared. Here’s one useful guide.