^T>o Insects and their Surroundings 



dividuals. In the case of the migrating hordes of 

 Locusts and Butterflies, however, the whole community 

 moves in concert. 



It has already been mentioned in this chapter 

 (p. 306) that the Digging-wasps hunt for caterpillars 

 or spiders which they carry to their nests, and seal 

 up in a cell with an egg, thus working to provide 

 food for their grubs in anticipation of hatching (194). 

 It has been suggested (195) that this habit has been 

 developed from that of the Ichneumon-fly who simply 

 lays her egg in or on the living insect which is to 

 form the food of her offspring. An intermediate 

 stage would be presented by an insect which captured 

 prey and then dug a hole wherein to bury it, laying her 

 egg beside it. The habit of most digging-wasps — 

 first preparing a hole and then hunting for food for 

 the grubs — marks a further development. Progress 

 in nest-making can be traced to a great extent among 

 the various genera of Wasps and Bees ; the primitive 

 unicellular nest is improved into a linear arrangement 

 of cells with a common opening, hollowed out either 

 in the earth or in twigs, as may be observed among 

 species of Crabro, Colletes, Osmia, etc. Another step 

 in advance is furnished by the branched type of nest, 

 in which the cells open off from the entrance or from 

 a main passage ; such nests are constructed by species 

 of Hoplopus, Halictus, etc. Nests made out of various 

 substances collected or secreted by the insects mark 

 the highest stage in the building-habit. The leaf- 

 cutter Bees {Megachile) nest in the earth, but within 

 the earthen cell they form a beautiful lining made 

 up of fragments of leaves, which they cut out with 

 great accuracy by means of their mandibles. Mason- 

 bees and certain slender wasps {Pelopcms) build, on the 

 surface of rocks or walls, nests composed of particles 

 of earth, sand, or lime, cemented together by the 



