WHEELER— THE PARASITIC ACULEATA. 5 



larger than in the females. It can hardly be claimed, however, 

 that the parasitic bee is psychically less endowed than its host, be- 

 cause the finding and entering of the latter's nest presupposes in- 

 stinctive activities of a high order. 



Our knowledge of the habits of parasitic bees is rather meager 

 when compared with our knowledge of the species as taxonomic 

 units. They occur in all parts of the world, but even the hosts of 

 many of the genera, especially of the nonholarctic forms, have not 

 yet been ascertained. Within recent years, however, Verhoefif 

 (1892), Hoppner (1904), and Graenicher (1905) have made some 

 careful observations on the behavior of a few European and North 

 American species. Verhoeff studied the activities of the Stclis 

 minuta larva in the nests of Osjuia Icncomelcrna which are in hollow 

 blackberry stems. The Osmia makes a row of cells in the cavity, 

 separating them with partitions of chewed up leaves, provisions each 

 cell with a ball of honey-soaked pollen, the socalled " bee-bread," 

 and lays an egg on it before closing the cell and starting another. 

 Graenicher summarizes Verhoeff's observations in the following 

 words : 



" I. Stclis minuta deposits its egg earlier than the host-bee, and in the 

 lower region of the bee-bread. 2. The larva of the parasite hatches a little 

 earlier than that of the host-bee, whose egg is situated on top of the bee- 

 bread. 3. Botli larvae, wliich at the beginning are of about the same size, 

 partake of the bee-bread, the host-larva on top, the parasite below. 4. The 

 latter gradually' increases in size, and consequently advances towards the 

 host-larva on top. 5. Finally the parasite, which in the meanwhile has become 

 twice as large as the host-larva, comes in contact with the latter, kills it and 

 eats it. Verhoeff informs us that there was a mutual exchange of hostilities 

 between the two larvae, each trying to grab the other with its mandibles, but 

 that finally the parasite succeeded in burying its mandibles in the head of the 

 host-larva. The latter was eaten up within i or 2 days." 



Hoppner's observations on the larva of Stelis ornatula in the 

 cells of Osmia parvida and lencomelccna agree essentially with Ver- 

 hoefif's, except that he saw no struggle between the parasitic and 

 host larva. The former bored its way upwards through the bee- 

 bread, sought out the Osmia larva as soon as possible and plunged 

 its mandibles into the body of the latter without meeting with any 

 resistance. Like Verhoefif he found the parasitic to be larger than 

 the host larva. 



