194 INTRODUCTION 
The following belong to the group :— 
1. Hymenoptera. Long-tongued digging-wasps (Fossores, e.g. Bembex, Ammo- 
phila) and ruby-wasps (Chalcididae, e.g. Parnopes), the solitary true wasps 
(Eumenidae, e.g. Eumenes, Odynerus, and others), short-tongued bees (Apidae, 
e.g. Andrena, Colletes, Dasypoda, Halictus, Panurgus, Prosopis, and Sphecodes, 
to which also may be added Camptopoeum, Dufourea, Halictoides, Melitta, Macropis, 
Nomia, and Panurginus). 
2. Diptera. Conopidae, Syrphidae, and Bombyliidae. 
3. Lepidoptera. All except the hawk-moths (Sphingidae), which belong to the 
next group. 
4. Coleoptera. Only a few exotic beetles such as Nemognatha. 
III. Eutropous Insects. Completely adapted flower visitors of the greatest 
value for pollination. They possess habits and structural modifications which further 
in high degree their own ends in plundering flowers, while at the same time they 
unconsciously effect cross-pollination in the most effective manner. They conduct 
their visits to flowers with the greatest constancy and regularity of movements. 
Corresponding to them in the plant world is an extraordinary variety of flower 
adaptations that can only be explained with reference to the regularly occurring 
cross-pollination effected by their visits. 
To this group belong :— 
1. Hymenoptera. Long-tongued bees (Apidae—Anthidium, Anthophora=Poda- 
lirius, Apis, Bombus, Ceratina, Chalicodoma=Megachile, Chelostoma = Eriades in 
part, Coelioxys, Crocisa, Diphysis=Trachusa, Eucera, Megachile, Melecta, Meli- 
turga, Nomada, Osmia, Psithyrus, Saropoda = Podalirius in part, Systropha, 
Tetralonia=Eucera (Macrocera), Trypetes=Eriades in part, Xylocopa, and also 
Rophites). 
2. Lepidoptera. Hawk-moths (Sphingidae). 
IV. Dystropous Insects. ower visitors not adapted to pollination. They 
are either—as some beetles (Chrysomelidae, many Lamellicornia, Curculionidae, and 
others), and also earwigs (Forficula)—wholesale flower devastators which devour 
floral structures, or else their habits are detrimental to pollination, as in the case of 
creeping flower guests (ants, aphides, thrips). It consequently follows that flowers 
possess protective arrangements repelling their visits but no adaptations facilitating 
them. There have in particular been developed in flowers a series of structures 
serving to prevent the entry of these unbidden guests, which are mostly nectar- 
thieves. 
Ants, which are described as dystropous by Loew, are not regarded as such 
by Verhoeff (‘BI. u. Ins. auf Norderney,’ p. 169), but Loew (‘ Bliitenbiol. Floristik,’ 
p- 387, note) calls attention to the fact that Hermann Miller in his ‘Alpenblumen’ 
also described ants as either valueless or harmful (+) for flowers, and of forty-three 
ant-visits he observed thirty-four were dystropous. 
Loew describes as Pseudodystropy the case in which, ‘even in completely 
eutropous forms, adaptations may be secondarily acquired which render their owner 
a devastator of flowers under special circumstances.’ A very well-known example is 
afforded by Bombus mastrucatus, which in the Alps gets at the nectar of many 
