From GoToCayman.com - the Wiki for Cayman
Bugs (Mosquitoes/sand flies etc!)
The Cayman Island's used to be famous for their mosquitoes. 36 different species have been recorded on the islands, and back in 1971 a record of 600 bites per minute on one arm were recorded (I pity the researcher who volunteered for that!).
Mosquitoes tend to be a problem around sunrise and sunset. At these times it is probably best to stay indoors, or make sure that as little skin as possible is exposed if you are out and about, or use Deep Woods OFF! spray or similar. An alternative is to take a daily dose of 500mg of vitamin B1, starting two weeks before you go on holiday and continuing throughout your stay; this will stop the mosquitoes from biting you.
Where you stay on the islands and the time of year you are visiting also has a bearing on how bad the problem is. The Seven Mile Beach area isn't as bad as some parts of the interior or around Rum Point, West Bay or East End. The problem is worse during the rainy season (May to November)
Many of the open-air bars/restaurants burn Citronella candles to keep the mosquitoes away. The Cayman Islands Government's Mosquito Research & Control Unit is responsible for carrying out preventive sprayings using their crop-dusting planes and a number of vehicles. Their web site also contains details of the mosquito breeds, where they breed, insecticides used in spraying, etc. Unfortunately their home page which is meant to show their spraying schedule hasn't been updated since 2005 :-(
Sometimes called no-seeums (You don't hear em and you don't see em), but you'll know when you're being attacked as you'll feel lots of itchy bity things on your scalp, arms, legs, etc. They are tiny, easily go through window screens, and love to bite. Again tend to be bad at sunset - take the same precautions as with dealing with mosquitoes.
NOTE: The number of bugs/mosquitos increased dramatically after Hurricane Ivan and it is taking time for the situation to get back under control.
You may be used to these at home, but out in the tropics they are BIG! As one of the oldest species on the planet, they can make their home just about anywhere. Their presence doesn't necessarily indicate dirt as I've seen them on a building site for a new home.
Since Hurricane Ivan, there have been increased sightings of scorpions on Cayman. As the hurricane and rising waters wrecked their habitiats, they have moved to new homes - often those already inhabited by humans! There are three species of scorpion found on Cayman: heteronebo caymanensis – an endemic species unique to Cayman; the most common, centruroides; and isometrus maculatus. There are no records of deaths from scorpion stings in the Cayman Islands, but scorpions should always be treated with respect, as even a non–fatal sting can be very painful. They like dark nooks and crannies - so give your shoes a shake before putting them on!
Thimble Jelly Fish/Sea Lice (Sea Itch)
Sea Itch is caused by the larvae (nematocysts) of the Thimble Jelly Fish (Sea Lice) and is an intensely itchy red rash which affects exposed areas of skin. Found in Caribbean waters from March to September, it is especially bad in Cayman waters around April/May. At these times it is best to wear a full skin wet suit when in the water and cover exposed skin with suntan oil or one of the specialist oils/preparations including Lands End Oil, WipeAway Jelly Fish Sting Medicated First Aid Gel and Sawyer Products Itch Balm Plus (all of these should be available from good dive shops). SeaSafe brand suntan oils are based on natural secretions of the clown fish. In scientific studies this has shown to greatly reduce, and in many cases completely prevent jellyfish stings.
Because the larvae are so small, they often manage to work their way under swimming costumes/wet suits. When the swimmer leaves the water, their garments press against their skin, causing the stingers to fire. Remove said garments as quickly as possible when leaving the water and rinse it thoroughly - preferably in warm water and detergent. Aquatic Wetsuits make a special Sea Lice wetsuit that has dry suit seals at the wrists and neck and special hood with a "neck dam" which further prevents water from flowing in with sea lice. If using a normal wet suit another suggestion is to apply vaseline around the wrists and neck and the hairline at the back of the neck where they get trapped into your hair. After leaving the water wash all swimwear thoroughly; let the water run for a couple of minutes to make sure that the nematocysts have been washed off. Avoid rubbing as this may 'fire' and larvae attached.
If you get stung, wash/rinse thoroughlt in hot soapy water, applying as little frictions as possible and dry with heat in a dryer (or drip-dry!). Putting on an unwashed swimsuit may mean that your are just reapplying more larvae to your skin. The standard treatment consists of application of steroid creams to the skin and taking antihistamine tablets. However, these tablets can cause drowsiness, so there is an increased risk of nitrogen narcosis if diving. Hydrocortisone cream can limit the itching. Alternative remedies include calamine lotion, gently blotting with amonia spray (such as Windex - the window cleaning spray), white vinegar, rubbing alcohol or urinating on the affected areas! Take a little Benadryl. If the symptoms get bad, go to the doctor and he will give you an effective "jab" to relieve the irritation.
Cruise ship passengers
Definite nuisance if you are trying to get around George Town. On some days there can be up to ten ships disgorging over 20,000 passengers. You can check cruise-ship movements at the Cayman Islands Port Authority web site at http://www.caymanport.com/schedule.htm
Invariable look the wrong way when crossing the roads, or drive on the wrong side of the road. Ask residents daft questions like "Do you live here, or do you fly in every day?".
Clog the roads to/from George Town in the morning (7am to 9am) and afternoon (4pm to 6:30pm) rush hours. A journey that would normally take 10 minutes can take an hour at these times.