A cheaper method to get rid of them is to inject them with lemon juice. You need a small bore syringe (which, depending on where you live, may be available for a nominal fee without a prescription from your local pharmacy...although when I bought mine they also gave me a pamphlet...about the dangers of sharing needles I felt like saying"No, really, it's for my saltwater tank!" "Really, sir, it's none of our business".) You need only a small amount, but have to move quick, or they withdraw. 100% success, plus you can actually use the lemon juice for other things...