The Eastern green mamba is a highly venomous snake native to the coastal regions of southern East Africa. It is a large snake, with a slightly compressed and very slender body with a medium to long tapering tail. The head is narrow, elongate, and coffin-shaped, with a distinct canthus that is slightly distinct from the neck. When threatened or otherwise aroused in some way, Eastern green mambas are capable of flattening their neck area, though no real hood is formed. The eyes are medium in size and the pupils are round. The dorsal scales are oblique, smooth and narrow. Adult Eastern green mambas have bright green upperparts and a pale yellow-green belly. Juveniles are blue-green, becoming brighter green in successive sheddings of the skin. The border of the pupil may have a narrow bright ochre to the golden yellow edge, and the posterior border of the iris may become bright green. The inside of the mouth may be white or bluish-white.
Eastern green mambas are native to more coastal regions of southern Africa and East Africa. Their range extends from Kenya south through Tanzania, Malawi, eastern Zimbabwe, and eastern Zambia. They can also be found in Zanzibar and northern Mozambique. An isolated and genetically distinct population is found in South Africa from the extreme northeastern part of Eastern Cape along the KwaZulu-Natal coastline and into southern Mozambique. Eastern green mambas inhabit tropical rainforests in coastal lowlands and it is suggested that they can also be found in coastal bush, dune and montane forest. These snakes are rarely found in open terrain and prefer relatively dense well-shaded vegetation. In addition to wild forest habitats, they are also commonly found in thickets and farm trees (such as citrus, mango, coconut, and cashew). In coastal east Africa, they are known to enter houses and may even shelter in thatched roof dwellings.
Eastern green mambas are solitary reptiles that are active during the day. They are primarily arboreal (living in trees), only rarely descending to the ground. Eastern green mambas are elusive snakes; due to their coloration, they are usually well camouflaged in trees or bushes. They are not commonly found on the ground unless motivated by thirst, prey, or the need to bask in the sun (thermoregulation). They are adept climbers and extremely agile snakes. They sleep at night in a tree coiled up in leafy clumps rather than seeking a tree hollow (although sometimes found in them). Eastern green mambas are relatively sedentary and can remain in the same location for days at a time, apparently moving most commonly to find food or mates. On average, individuals of this species move only about 5.4 meters (18 ft) per day. Eastern green mambas are shy creatures and tend to avoid confrontation with humans or other predators when possible, by relying on camouflage or fleeing. They are fast snakes, capable of moving 11 kilometers (7 mi) per hour. They are reluctant to strike but may do so repeatedly in quick succession if provoked or cornered, often leading to severe envenomation.
Eastern green mambas are carnivorous reptiles. They prey primarily on birds and their eggs as well as small mammals including bats. It is believed that these snakes eat arboreal lizards as well.
Eastern green mambas start breeding during the rainy season, between April and June. Gravid (pregnant) females tend to be sedentary, but males actively search out and court prospective mates. Males may fight each other over potential mating opportunities, or possibly to establish a dominance hierarchy. Typically, a male initiates a fight by moving on top of the other’s body and tongue-flicking, after which the two snakes twine together and push in an attempt to pin each other's head to the ground. Male-male combat can last for several hours. Males locate females by following a scent trail. The male courts the female by aligning his body along the female’s while rapidly tongue-flicking. Courtship and mating take place in the trees, after which the female lays anywhere between 4-17 eggs, which occurs in the summer months of October and November. The eggs are usually laid in a hollow tree, among decaying vegetation, or leaf litter. The incubation period is 10-12 weeks. When the young emerge from the eggs, they are approximately 30-40 cm (12-16 in) in length. Hatchlings tend to grow 50-80 centimeters (20-31 in) in length in the first year of life. As the hatchlings age, their growth rates decrease but they never completely stop growing.
Although populations of the Eastern green mamba are stable overall, these snakes still face some threats which include habitat destruction and deforestation. In South Africa, their habitat is fragmented and being transformed into coastal housing developments.