168 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 hemztropy—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 wasps, 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 zchneumons (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 zchneumon 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 dystropous. 
Forms other than bees among Hymenoptera, which Hermann Miiller 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 office, 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). 
