The Turks and Caicos Islands are formed by two undersea pillars. The first, and largest, forms the Caicos Islands and the Caicos Banks, a huge shoal of 30-50 ft (9-15 m) depth that extends for miles south of Providenciales. The second, smaller pillar forms the Turks Islands, of Grand Turk and Salt Cay.
The islands themselves are of coral origin and are generally low-lying. This results in the rock being similar to limestone. It is white-coloured, and very soft. You'll see the bushes next to unpaved roads coated in the fine white dust caused the stone wearing away from vehicle travel. This same stone also results in the islands having some of the best beaches in the world, with soft, delightful sand, perfect for collecting in suitcases.
On the land, the Turks and Caicos receive little rainfall. There are a lot of mangrove swamps and salty bogs that are important for birds and young sea animals. On a few of the smaller islands or cays, rock iguanas can be found. On the larger islands, most places are rocky with indifferent dusty soil. Despite this, a wide variety of short plants quickly cover any unattended area, turning it into a dense 10' high jungle. The primary plants are Lignum Vitae, a tree that produces wood so hard and dense it sinks in water. The largest trees commonly found are "pod trees", which are, unbelievably, a legume like beans or peas.
It's usually hot and dry (except in the ocean!), with little rain. Because of the islands size and location, there aren't small drizzly rains often as on some wetter islands in the Eastern Caribbean. This location also means the islands are not often hit by hurricanes.
There are no poisonous insects in the Turks and Caicos, although there can be scary 12" (30 cm) centipedes hiding under stones in the remote areas of the islands. The only snakes found are tiny "toy" boa constrictors that are usually about 15" long, but you are unlikely to see any of these.
There are no endemic tropical diseases, and you don't require any vacinations to visit.