ANT-NESTS. 



209 



the interior has been eaten out by the Cynipid larva, the imago of which 

 leaves the gall by a circular aperture in its side. Hundreds of recently 

 fertilized females of several different species of ants annually take up 

 their homes and start their formicaries in these hollow spheres. On ex- 

 amining several thousands of these galls in the vicinity of Austin, 

 Texas, I found a considerable percentage of them inhabited by colonies 

 of the following ants which are here enumerated in the order of in- 

 creasing frequency: Leptothorax fortinodis, Lcptothora.v obturator, 

 Colobopsis etiolata, Cremasiogaster clara, Ccunponotus dccipicns, Cain- 



FIG. 115. Colobopsis etiolata of Texas. (Original.) a. Soldier in profile; b. head 

 of same, dorsal view ; c, head from anterior end ; d, worker. 



ponotns rasilis. The species of Lcptotlwra.v and Colobopsis, which 

 never form large colonies, inhabit the galls permanently, the Crcmasto- 

 gastcr and Camponotus use them mainly during the incipient colonial 

 period. Two of the species, L. obturator and C. etiolata are especially 

 interesting on account of their methods of modifying and guarding the 

 nest entrance. The former ant is very small, and the solitary female 

 on entering the gall finds the opening made by the gall-fly inconveniently 

 large. She therefore plugs it up with wood-fillings mixed with saliva. 

 When the small workers of her first brood hatch, they perforate the 

 middle of the diaphragm with an opening just large enough to permit 

 their bodies to pass in and out (Fig. 113). Occasionally this same ant 

 nests in twigs of the hop-tree (Ptcleatrifoliata} that have been hollowed 

 out by a small carpenter bee (Ccratina nana}. In such nests the larger 

 opening at the end of the twig is occluded and then perforated in the 

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