TROPICAL NATURE IN COLOMBIA 



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free spine on the pectoral fins which enables them to cling tightly to the 

 rocks ; the caddis fly larvae are all fastened firmly by threads ; the water 

 bugs are greatly flattened so that when they cling to a rock their bodies 

 offer little resistance to the water. On the surface of the brooks enor- 

 mous hairy spiders with ridiculously small bodies hunt for a living. 



The tree frogs in the mountains were hard pushed to find a place to 

 breed, for there was no standing water on the ground. They either car- 

 ried their eggs on their backs or laid them in the bases of bromeliads. 

 Many of the aquatic animals which are characteristic in other parts of 

 the world are lacking in the mountain streams. There were no snails, 

 pill bugs, or amphipods. The fauna was a specialized one — limited 

 mostly by its ability to avoid being swept away. 



In the slow rivers of the lowlands the most characteristic animals 

 were the shrimps and prawns which often possessed greatly elongated 

 claws. Curious little shrimps belonging to the family Atyidse were quite 

 common. These crustaceans have the first two pairs of legs modified into 

 little brush-like forceps with which they scrape the microorganisms from 

 the soft bottom or from aquatic plants. Many land and freshwater crabs 

 lived along the shores of the rivers. Among these Cardiosoma guahumi 

 was most conspicuous on account of its blue color and large size. This 

 big crab digs holes in the mud beneath the trees near the mouths of 

 rivers. It comes out at night seeking food and climbs the trees to eat the 

 leaves. It was a great sight to watch hundreds of these crustaceans on 

 the mud flats, sitting motionless in the glare of the jack-light. 



Along all the streams below 2,500 feet there were many lizards of the 

 genus Basiliscus. These animals have a very long slender tail and small 

 front legs. When disturbed they stand nearly upright and run swiftly 

 over the surface of the water, using only the hind legs and the tail, like 

 the ancient dinosaurs. In the trees along the rivers we encountered 

 many iguanas. These big lizards sit in the trees and if disturbed often 



A Land Crab, Cardiosoma guahaumi. 



