30 HYMENOPTERA chap. 



Fabre has made us acquainted with some points in the history of 

 another species of the same genus, viz. Stelis nasuta, that show a 

 decided departure from the habits of ^S. minuta. The first-named 

 Insect aceomphshes the very difficult taslv of breaking open the cells 

 of the mason-bee, Chalicodoma muraria, after they have been sealed 

 up, and then, being an Insect of much smaller size than the Chali- 

 codoma, places several eggs in one cell of that bee. Friese informs 

 us that parasitic bees and their hosts, in a great number of cases, 

 not only have in the perfect state the tongue similarly formed, 



but also frequent the same species 

 of flower ; thus CoUetes daviesanus 

 and its parasite Upeolus variegatus 

 both specially affect the flowers of 

 Tanacetum vulgare. Some of the 

 parasitic bees have a great resem- 

 blance to their hosts ; Stelis signata, 

 for instance, is said to be so like 

 Anthidium strigatum that for many 

 Yui.^5.^N'omadasex-fa£ciaia 9- years it was Considered to be a 

 -^'''*^"^- species of the genus Anthidium. 



In other cases not the least resemblance exists between the 

 parasites and hosts. Thus the species of Nomada that live at 

 the expense of species of the genus Andrena have no resemblance 

 thereto. Friese further tells us that the Andrena and Nomada 

 are on the most friendly terms. Andrena, as is well known, 

 forms populous colonies in banks, paths, etc., and in these colonies 

 the destroying Nomada flies about unmolested ; indeed, according 

 to Friese, it is treated as a welcome guest. He says he has often 

 seen, and in several localities, Nomada lathhuriana and Andrena 

 ovina flying peacefully together. The NomaAa would enter a 

 burrow, and if it found the Andrena therein, would come out and 

 try another burrow ; if when a marauding Nomada was in a 

 burrow, and the rightful owner, returning laden with pollen, 

 found on entering its home that an uninvited guest was therein, 

 the Andrena would go out in order to permit the exit of the 

 Nomada, and then would again enter and add the pollen to the 

 store. Strange as this may seem at flrst sight, it is really not 

 so, for, as we have before had occasion to observe, there is not the 

 slightest reason for believing that host Insects have any idea 

 whatever that the parasites or inquilines are injurious to their 



