Madagascar's largest snake is the ground boa, Acrantophis madagascariensis.  It's found in the east and north, often in the proximity of water in forested regions.  Browns and reds help it blend with the environment there remarkably well. 

The specimen at right is about five feet (1.5 m).  It was found cryptically lying exactly as shown in the forest leaf letter during mid-afternoon, distended with a large food bulge that felt like a fruit bat.  Easy to see, right?

Now try to find another ground boa in the below image, taken in the snake's natural habitat at the base of Montagne des Francais near Diego-Suarez.