gions, where the summers 

 are so short that the ants 

 have to utiHze every bit of 

 mid-day heat in order to 

 bring their young to ma- 

 turity. 



The mound is riddled with 

 chambers and galleries and 

 is not only fully exposed to 

 the sun, so that its tem- 

 perature is several degrees 

 higher than that of the sur- 

 rounding soil, but its slopes 

 are often constructed in such 

 a manner to catch the heat 

 rays perpendicularly and 

 form the most effective re- 

 gions of the heavens. This 

 orientation of the nests is 

 indeed often so conspicuous 

 and definite that they can be 

 used as compasses (see pic- 



Photo by the Author 

 larvae; of the TEXAN AGRICULTURAL ANT (PogOflO 



myrmex molefaciens) 



The brilliant white color and tensity of the skin in these tures, pages 742, 759). 

 grub-like creatures is due to the great accumulations of fat, Jn the tropics where the 

 which will be used in part at least, during pupation in buUd- sQii jg often saturated or 



mg up the body of the adult ant - 



diameters. 



Magnification about five 



ANTS THAT BUILD INCUBATORS 



Ants no doubt originally nested in the 

 earth, and the majority of species still 

 prefer this habitat. It was while living 

 in this plastic material that they learned 

 to prefer irregular galleries and cham- 

 bers and to become great opportunists, in 

 marked contrast with the social wasps 

 and bees, which have never been able to 

 depart from their habit of rearing their 

 young in combs made of a refractory sub- 

 stance like paper or of an expensive se- 

 cretion like wax. 



The ants early discovered the great ad- 

 vantages of being able to carry their 

 brood from place to place when danger 

 threatened. 



In connection with this free method of 

 dealing with the brood, they were also 

 led to add to the original subterranean 

 nest a kind of tepidarium or incubator, 

 in which the young could be placed dur- 

 ing the warmest hours of the day for the 

 purpose of hastening their development 

 (see pictures, page 759). This incu- 

 bator is the mound or dome of pebbles or 

 vegetable detritus, which surmounts the 

 subterranean nest of many of the more 

 conspicuous species of North America 

 and Eurasia, especially in mountain re- 



flooded with water during 

 the rainy season, and where 

 devices for conserving the heat are quite 

 unnecessary, many ants have learned to 

 construct paper nests on the trees. Such 

 nests superficially resemble the nests of 

 wasps. They contain no combs, how- 

 ever, but only a maze of irregular, inter- 

 communicating galleries and chambers. 

 A few tropical species belonging to three 

 different genera (CEcophylla,Myrma, and 

 Camponotus) inhabit nests consisting in 

 part at least of a fine silken web. 



REPAIRING THE NEST WITH SILK 



It was long a mystery how ants could 

 manufacture silk, but it has been recently 

 shown that the ants themselves do not 

 spin the silk, but use their larvae for this 

 purpose. The process can be actually 

 observed by making a rent in the wall of 

 the nest and then following the move- 

 ments of the ants under a magnifying 

 glass. They separate into two brigades, 

 one of which stations itself on the outside 

 of the nest and draws the edges of the 

 rent as close together as possible by pull- 

 ing with claws and mandibles, while the 

 other, inside the nest, moves the spinning 

 larvae back and forth across the gap till 

 it is filled out with a dense felt-work of 

 extremely fine silken threads (see picture, 

 page 764). 



754 



