The US Virgin Islands are full of amazingly beautiful sandy beaches. And those beaches are often infested with small biting and blood sucking insects sometimes called No See Ums, Sand Flies, as well as many other names.  They are almost invisible but their bites can swell up and look like mosquito bites.  They can also carry/transmit diseases. They are also not fast, if you are moving quickly into the water, you'll likely not get bit, but its when you walk back through the sand, sit on a towel, or have stand sticking to you or your shoes that they can hitch