About two thirds of Malaysia is covered in forest with believed to be 130 million years old. It is composed of a variety of types, although they are mainly dipterocarp forests. Dipterocarps can grow to about 50 m (164 ft) tall. Lowland forest occurs below 760 m (2,493 ft), and formerly East Malaysia was covered in such rainforest, which is supported by its hot wet climate. There are around 14,500 species of flowering plants and trees. Besides rainforests, there are over 1,425 km² (550 mi²) of mangroves in Malaysia, and a large amount of peat forest. Coastal land of the peninsular is fringed by mangroves, which cause sediment buildup resulting in peat bogs. These provide a base for plants that can tolerate the conditions. The peat forests of coastal Malaysia provide an important habitat for water birds and fish. The dipterocarps that occur in the peat forest obscure the ground, limiting ground vegetation. At higher altitudes, oaks, chestnuts, and rhododendrons replace dipterocarps.
There are an estimated 8,500 species of vascular plants in Peninsular Malaysia, with another 15,000 in the East. The forests of East Malaysia are estimated to be the habitat of around 2,000 tree species, and are one of the most biodiverse areas in the world, with 240 different species of trees every hectare. Further inland, heath forests are present. These forests host many members of the Rafflesia genus, the largest flowers in the world, with a maximum diameter of 1 m (3 ft). They also contain large numbers of carnivorous plants, such as pitcher plants, bladderworts, sundews, and ant-house plants.
Malaysia is a megadiverse country with a high number of species and high levels of endemism. It is estimated to contain 20% of the world's animal species. High levels of endemism are found on the diverse forests of Borneo's mountains, as species are isolated from each other by lowland forest.
There are about 210 mammal species in the country. Among these mammals are the Indochinese tiger, clouded leopard, the sun bear, the Sumatran rhinoceros, the Malayan tapir, mouse deer, barking deer, sambar deer, wild boar, bearded pig, gaurs, Asian elephants, red squirrels, lesser moon rats, Sunda otter civets as the primary predators. High levels of endemism are found on the diverse forests of Borneo's mountains, as species are isolated from each other by lowland forest. Kinabalu ferret-badgers, Kinabalu black shrews, Hose's palm civets, and Brooke's tree squirrels are all endemic to the mountains. Other small mammals include mongoose and giant rats. 11,300 orangutan's are found in East Malaysia. Other ape species include the white-handed gibbon and the siamang. Malaysia has 10 monkey species, divided between langurs and macaques. Proboscis monkeys, the world's largest monkey, are a langur species endemic to Borneo. Macaque species include the crab-eating macaque and the pig-tailed macaque. The world's largest cattle species, the seladang, is found in Malaysia. Fruit bats are also found throughout the country, with a high concentration in the Mulu Caves.
Over 620 species of birds have been recorded in Peninsular Malaysia, with many endemic to the mountains there. Bornean forests show high levels of endemism among bird species, with 38 species found nowhere else. Black-browed babblers and white-crowned shamas found only in these forests. Large numbers of hornbills (nine species), woodpeckers, and pittas, such as the mangrove pitta are also present. Other species are found isolated on mountains, such as golden-naped barbets, spot-necked bulbuls, and mountain serpent-eagles. Bulbuls, starlings, and house swifts can be found in urban areas. The fish eagle and brahminy kite are the most common birds of prey. Storm's stork and the oriental darter can be found in wetlands.
250 reptile species have been recorded in the country, with about 150 species of snakes and 80 species of lizards. Only 16 of the land snakes are venomous. Notable among these are the Malayan pit viper, king cobras, Dumeril's monitors, Malay water monitors, and estuarine crocodiles. The king cobra is the deadliest snake found, but it is rarely encountered. The reticulated python is said to grow up to 10 m (33 ft) in length. Monitor lizards, almost 2 m (7 ft) in length, are found in both halves of the country. Other snake species include the paradise tree snake and Wagler's pit viper. Estuarine crocodiles can grow up to 2.5 metres (8.2 ft) in length. Its smaller relative, the Malayan false gharial, can also be found. Flying lizards can also be found.
There are about 150 species of frog in Malaysia. Freshwater fish include the rare Asian arawana, along with marbled gobys, harlequins and tiger barbs.
Malaysia has thousands of insect species, with more being discovered every year. Butterfly species include the Rajah Brooke birdwing, while moth species include the atlas moth. The largest beetle found is the rhinoceros beetle. Other large insects include the giant stick insect, which can grow as long as a human forearm, the empress cicada, with a wingspan of 30 cm (12 in), and the 4 cm (2 in) long giant ant. Other insects include banded hornets, fire ants, giant honey bees, and weaver ants. Many scorpions can also be found.