342 ANNUAL REPOET SMITHSONIAN INSTITUTION, 1915. 



Meliponas and the Trigonas have achieved great economy in con- 

 struction; instead of using for all purposes the hexagonal cells, 

 made with great labor and with mathematical precision, they re- 

 serve these for the larvae only, constructing simpler cells for provi- 

 sions. The nests of Meliponas built in hollow trees are sometimes 

 over a meter long. If the hollow of the tree is too large, they limit 

 it at one end or the other by making a wall, but instead of using the 

 wax for this purpose, since this is made only with great labor, they 

 utilize earth agglutinated with a liquid which they secrete. This 

 same mixture is used to reduce the size of the entrance to a simple 

 little hole, allowing the passage of only one bee at a time, and at 

 night this opening is closed. These precautions are justified by the 

 absence of a sting, which renders them defenseless. The cells of the 

 larvae, in the middle of the nest, always opposite each entrance, are 

 specially protected by lamellee of fine wax, and, as we have just 

 said, are surrounded by provision cells shaped like pots. A^Hiere 

 the Meliponas can not find hollow trees they build by the aid of the 

 mixture just mentioned — earth and the special secretion (pro- 

 polis) — a true nest, with irregular branching galleries, which has 

 some resemblance to a white ant's nest. 



A peculiar habit is found among the Xylocopas, a species related 

 to the Meliponas. These creatures, the largest of the big bees, are 

 found in the warmer portions of Africa, Asia, and America. They 

 make their nests in old trunks of trees and in dead wood which they 

 bore with their strong jaws. In the gallery made in this way, the 

 female brings together a mass of honey and pollen intended for 

 larval food. On this mass an egg is laid, and then the chamber is 

 closed by a wooden partition which becomes the bottom of the next 

 chamber. In this way she builds a column consisting of a series of 

 superposed cells. After about three weeks the larva becomes full 

 grown and transforms into a pupa in the interior of a cocoon. The 

 larva in the lowest cell, the oldest, is from that fact the first to be 

 ready to issue as an adult bee. But how can it get out? Must it 

 wait until the younger larvae has transformed, or does it eat its way 

 out through the upper cells at the risk of killing all of its brothers 

 and sisters? Here the insect shows a very special adaptation, as 

 though it appreciated the danger to which such a passage would ex- 

 pose the other larvae, and adopts another road. With its strong 

 mandibles it opens a passage at right angles to the floor, and the 

 others follow by the same road, each one eating through the partition 

 of its own cell, and thus the whole colony finds itself liberated 

 through the industry of the first one. 



Even more than the bees, the social wasps astonish us by their 

 artistically constructed nests, and it is rare to find insects with such 

 bellicose habits devoting themselves so conscientiously and peacefully 



