The Desertas Islands comprise three islands: Ilhéu Chão, Deserta Grande and Bugio.
The Ilhéu Chão is the smallest of the three islands. It presents the plateau form, with an almost constant altitude of 80 meters, reaching a maximum of 98 meters in the extreme north, where there is a Lighthouse. To the north, is an islet with 50 meters of altitude, denominated of Farilhão. It is approximately 1600 meters long and 500 meters wide.
The Great Desert has an elongated shape, and is the largest and tallest of the three islands. It develops in an extension of 11700 meters from Ponta da Castanheira in the north, to Ponta do Tabaqueiro, in the south, with a maximum width of 1900 meters. It reaches a maximum altitude of 479 meters. Along the coast are innumerable caves excavated in the rock, small beaches and some fajãs. The largest fajãs are the Fajã Grande and the Fajã da Doca, which resulted from simultaneous collapses of lands, west and east, occurred in 1894.
The Bugio is long and narrow and is shaped like a bow. It is the most rugged and jagged of the islands. It stretches along 7500 meters in length from Ponta do Cágado to the North to Ponta da Agulha to the South and reaches the maximum width of 700 meters. The maximum altitude is 388 meters.
The Deserta Grande wolf spider, is a critically endangered spider species endemic to the Deserta Grande Island of the Madeira archipelago – specifically a remote valley, the Vale de Castanheira. Adult numbers have been estimated at less than 5,000, making it one of the rarest wolf spider species. It is also believed to be one of the largest wolf spiders on earth, with a 12 cm (4.7 in) leg span for the female, somewhat smaller for the male (the Latin ingens means “huge” or “monstrous”). Coloration is grey and black with white spots on the legs. The spider hides under rocks and crevices on this volcanic island