In true deserts, most of the land has no plant life, the annual rainfall ranges from 0-1.5 centimetres (0-6 inches), the daytime heat is intense and the nighttime temperatures are freezing.
Semi-deserts have 1.5-3 centimetres (6-12 inches) of rain annually on average, usually only falling in one or two months of the year.
Deserts can be hot, cold semi-arid, or coastal.
Plants may be scarce in most deserts, but the seeds of plants lie dormant for years. They sprout during the times of rain.
Plants in semi-deserts usually consist of dwarf shrubs, irregular growths of short grasses, and sparse trees along river beds.
Deserts have sand dunes, gravel, and rock.
Animals in deserts and semi-deserts need to have ways to keep cool, and to find enough food and water to survive.
Many desert and semi-desert animals are nocturnal (active at night) and keep cool in burrows underground. Some remain dormant and are active during the rainy season.
Some animals that like deserts or semi-deserts include kangaroo rats, antelopes, camels, foxes, jackals, coyotes, lizards, and snakes.
Insects live in deserts and semi-deserts. These include flies, beetles, ants, termites, locusts, and grasshoppers. Millipedes and centipedes also live in deserts, and so do arachnids, such as scorpions, and spiders.
Birds are better at adapting to deserts than mammals, because birds can fly to seek food and water. Birds can also fly in the cool thermals of air, high above the ground.
Some desert birds run instead of fly. These include sandgrouses, desert larks, ostriches, and coursers.
Photographer: Martina Nicolls
Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM