2i6 THE BIOLOGY OF INSECTS 



Like the wasps the great majority of bees provide for their 

 young by storing food — honey and pollen — in the nests 

 wherein they lay their eggs, the nests being made in tunnels 

 excavated in the soil, by species of Andrena, CoUetes, and 

 Megachile for example, or in the twigs of plants as by the 

 well-known Osmiae, or in dry wood as by the " carpenter '* 

 bees (Xylocopa), or in remarkably firm structures of stone- 

 fragments and cement as by the '* mason " bees (Chalico- 

 doma). Among all these the nest- chamber is sealed up 

 with the egg a- d the store of food, and the mother bee never 

 sees her offspring. The habits of Osmia tridentata, as 

 described by J. H. Fabre (1891), afford an example of what 

 may be regarded as family relationship. The female of 

 this species lays eggs in a series of chambers along a hollow 

 bramble-stem, each chamber with a provision of food for 

 the grub after hatching, and the grub when fully grown spins 

 a cocoon and pupates. When a young bee emerges from 

 the pupal coat, it bites its way through the cocoon, and then 

 through the partition closing the chamber in which it has 

 been reared. Should the young insect be in the last- 

 formed chamber next the opening of the hollow twig, it 

 comes out at once into the open and begins its active aerial 

 life. If, however, it finds the way to liberty blocked by the 

 cocoon of a younger sister it waits for her emergence or tries 

 to press a way between her cocoon and the wall of the 

 chamber ; it is stated that a young Osmia never injures 

 other members of the family in attempts to escape from its 

 nest. Although the last-laid egg is nearest to the outlet 

 and the first-laid in the nest farthest from it, the young do 

 not necessarily complete their development in the regular 

 order that might be expected ; the older offspring may have 

 to wait comparatively long for the emergence of their younger 

 sisters, or these latter may complete their transformations 

 more rapidly than those hatched from the earlier laid eggs 

 and so get out of the way in good time. 



It is of interest to note that the perfect insects among 

 the Hymenoptera commonly take food of the same kind as 

 they provide for their larvae. Bees as well as bee-grubs 



