1921] Wheeler: Some Social Beetles 101 



all other species of the genus Xylehorus, is remarkably small. 

 There are usually not more than three males in the largest 

 colonies, or groups of brood-chambers. It would appear from 

 observations made by Swiner and Eichhoff in Germany, and 

 the numerous colonies I have examined in this country that there 

 is, on an average, about one male to twenty females. The males 

 have no wings, therefore probably do not leave the brood-cham- 

 bers, but remain with the over-wintering colony until all have 

 emerged in the spring. They are then left to be smothered in 

 overabundant ambrosial food, or to the tender mercies of preda- 

 tory insect enemies which had previously been prevented from 

 entering the brood-chambers by one or more female sentinels 

 at the entrance. A few females may emerge from time to time 

 during the summer to start new colonies, but from the excessively 

 crowded condition of the brood-chambers during the fall and 

 winter months, it would appear that the older adults of the 

 broods excavate branching chambers in which new broods are 

 developed, and that in these old and new chambers they pass 

 the winter." 



The third group of social beetles comprise the large 

 Lamellicorns of the family Passalidze, abundant in the tropics 

 of both hemispheres but represented in the United States by 

 only a single species, Passalns cornutus Fabr., which ranges as 

 far north as Massachusetts and Illinois. None of our Coleop- 

 terists seem to have taken the trouble to study the habits of this 

 common and conspicuous insect, so that it was left to Ohaus 

 (1899-1900, 1909) to discover the social behavior in certain 

 Brazilian species. He found that they live in rotten logs in 

 colonies, each consisting of an adult male and female with their 

 larvae. The beetles excavate spacious galleries, comminuting 

 the wood and probably treating the particles with some digestive 

 enzyme, so that they can be eaten by the larvae, which slowly 

 follow along the galleries just behind their tunneling parents. 

 Owing to the structure of their mouthparts the larvse are quite 

 unable to break down the wood, and when removed from their 

 parents soon die. The beetles not only guard their greenish eggs 

 and diligently provide food for their larvse, but also protect the 

 pupae and feed the imaginal young till their chitinous integument 

 is completely hardened. In a former paper (Wheeler and Bailey, 



