To prevent use Safe Sea (safesea.net), you can buy it on the interent, not sure if you can get it on the island. We brought it last year in April, used it the first two days, but didn't run into any. Did meet one lady that had it where her wet suit ended around her neck. Seems the affected areas are where they get trapped by clothing. Check with your guides as well, some will carry a spray bottle of ammonia just in case.