198 THE SNAKES OF SOUTH AFRICA. 
single snake. Mambas are very sociable, several males and 
females being frequently found inhabiting the same hollow in the 
trunk of a tree, a crevice among boulders, or a hole in a bank. 
Mr. Jones tells me he has found as many as half a dozen pairs 
inhabiting the same hole. He says they have no objection to 
residing beside the true Cobras, as he has often found Black 
Mambas and Cobras (Nava migricollis) sharing the same retreat. 
How AND WHy THEY CHANGE CoLouUR—A THEORY. 
The female Mamba lays its eggs in the dense bush, where the 
young, when hatched, will have fewer natural enemies than if in 
more open localities. The young take to the trees, and would, 
most likely, haunt the woodlands until nearly adult, when the 
struggle for existence becoming keener, they or many of them, 
would wander further afield for food, which had hitherto been 
chiefly birds, their young and eggs, chameleons and other tree 
lizards. On leaving the dim, moist, and shady forest, and 
venturing out into the open country, the strong actinic rays of 
light from the sun would very soon cause the vivid green pigment 
of the skin to assume an olive tint, which would subsequently 
darken and become the characteristic colour of the Black Mamba. 
In Mamba infested forests in Zululand where Black Mambas 
abound, there are many open bare spaces upon which Black 
Mambas bask in the hot sun. This habit of lying exposed to the 
strong rays of sunlight might have been a contributing cause to 
the determination of their colour. 
Green, especially the more vivid shades, is rapidly acted upon 
by strong white light. The fresh skin of a Green Mamba, if placed 
in a strong light, will rapidly change to blue or olive, then to 
olive-black. If dried in a dark place, rolled up and packed away, 
it will retain its green colour. 
There are males and females amongst the green and black 
varieties of Mambas. Eggs have been found in both varieties. 
The question of colouration in snakes is a very puzzling one. 
We find Mole Snakes (Pseudaspis cana) of several colours. Some 
are uniform shiny black, others are reddish-brown, brownish- 
black, or brown mottled and waved with black, and sometimes 
spotted and lined with white. 
The Boomslang or Tree Snake (Dispholidus typus) also differs 
