i68 INTRODUCTION 



group that this organ and the labial palps are obviously long and narrow, while in the 

 genus Pterocheilus a peculiar feathering of the latter is also seen. Only this group 

 can therefore be placed on the adaptational level of the fossorial wasps — the stage 

 described by Loew as hemiiropy — while the social wasps, owing more particularly 

 to their omnivorous habits, do not display any obvious adaptations enabling them 

 to pilfer flowers successfully — a condition which Loew terms allotropy (cf. p. 193). 

 On the other hand, certain flowers are visited by wasps with marked predilection, 

 so that Hermann Miiller was able to establish a special group of ' wasp flowers ' 

 (see pp. 119-20), the visitors of which, however, belong to many other groups of 

 insects besides 'wasps.' 



The visits of true wasps to flowers, like those of fossorial v^asps, are made in 

 order of decreasing preference to flowers with exposed or partly concealed nectar, 

 flowers with completely concealed nectar, social flowers and wasp flowers, while bee 

 flowers and pollen flowers are most avoided. 



The ichneumons (Ichneumonidae) are only casual flower visitors, but at the 

 same time they display a certain preference for particular species, so that these may 

 be described as ichneumon flowers (cf. p. 121). Saw-flies (Tenthredinidae), like 

 ichneumons, are only occasional allotropous flower visitors. Details have already 

 been given (pp. 103-5) with regard to the peculiar part played by certain fig-insects 

 (Blastophaga, Sycophaga) in the pollination of figs. 



Among the Ruby wasps (Chrysididae) the genus Parnopes has a longish proboscis 

 adapted for visits to flowers, while species of the other genera, though not infrequently 

 met with on flowers, are of no importance as' agents of pollination. The Wood 

 wasps (Siricidae) which belong to this group have not yet been observed visiting 

 flowers. 



Ants (Formicidae), lastly, frequently occur as ravagers of flowers, for which 

 reason Loew has termed them dysiropous. 



Forms other than bees among Hymenoptera, which Hermann Muller places 

 together (' Alpenblumen,' p. 518) under the name of ' wasps,' mainly visit in the Alps 

 flowers with directly visible nectar, where they chiefly come into competition with 

 beetles and short-tongued flies. On pollen flowers only saw-flies and true wasps 

 were met with, but these appeared to be attracted by the chance of capturing flies 

 rather than by the pollen. On alpine lepidopterid flowers saw-flies occur, as well 

 as true wasps, and also occasional ichneumons, though these benefit neither them- 

 selves nor the flowers. Ants insinuate themselves into flowers not infrequently, and 

 sometimes reach the nectar. But they are, as a rule, quite useless as agents of 

 pollination, not only for these flowers, but also for others they visit. This is partly 

 because they are too small for this oSice, and partly because they go on foot, and 

 stay for a long time at any supply of nectar they may have found. Ichneumons 

 and solitary true wasps use the holes bitten by Bombus mastrucatus in bee flowers, 

 and share the stolen nectar, so that they too may be regarded as mere enemies to 

 bee flowers. Social wasps (Polistes, Vespa), on the other hand, are not found on 

 the most highly specialized bee flowers, but considered as agents of pollination 

 are practically divided between such of these as are of lower grade (Rubus 

 Idaeus and R. Saxatilis, CH) and wasp-flowers (Cotoneaster vulgaris, Lonicera 

 alpigena, Hw). 



