Bugs, Bites & Other Wildlife Concerns -- The biggest menaces on all three islands are mosquitoes (none are disease vectors) and no-see-ums, which appear mainly in the early evening. Window screens aren't always sufficient, so carry insect repellent.
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I don't find them any worse than at home. If it rains, there's more. If it's dry, there's less. Dengue fever has been reported on the island and is caused by Aedes aegypti, a domestic, day-biting mosquito.
Avoid walking/sitting on the beach or the area near where the sand meets the vegetation at dusk/dawn as those are the times sand flees/no-see-ums are most active. Just got back from 3 weeks. Stayed in the Simpson Bay area but was all over the island.
You won't need bug spray for certain activities in the Caribbean. You are unlikely to need it on the ship at all. If you go to a beach or on an ocean boat tour such as snorkeling, scuba, sailing between 10am and 3pm, you will not need it.
I would avoid anything in Marigot, Sandy Ground, Nettle Bay, Dutch and French Quarters, Lower and Upper Prince Quarter, Cole Bay, Mary's Fancy, etc. These are locals areas and not much there for tourists. I am not sure there ARE AirBnBs in those areas but there could be.
The area is one of the richest waters for shark spotting in the world. With a little luck, you can meet dozens of nurse sharks or perhaps the elegant Caribbean reef shark during a dive, but that's not it; you can also come across ground and tiger sharks.
More recently, a 2005 study showed there was no evidence it influenced the attraction of mosquitoes to human skin-derived chemicals from volunteers taking vitamin B supplements. There is simply no evidence taking vitamin B will offer any significant protection from mosquito bites.