Insects in Great Britain . 
229 
[ 6 . Flowers specially adapted to Diptera (D) ; Veratrum 
album , Saxifraga umbrosa 1 .] 
7. Flowers specially adapted to Bees (H); most Labiatae, 
Echium , Gentiana. 
8. Flowers specially adapted to Lepidoptera (F) ; Silene 
acaulis , Gymnadenia . 
Similarly the insects visiting the flowers are divided into 
classes according to their degrees of specialization for flower- 
visiting. The chief groups are : — 
1. Neuroptera, Orthoptera, Hemiptera, Thysanoptera. 
2. Coleoptera. 
3. Long-tongued Diptera (Syrphidae, Conopidae, Bomby- 
lidae, Empis). 
4. Short-tongued Diptera (all others). 
5. Long-tongued Bees (Apis, Bombus, &c.). 
6. Short-tongued Bees (Prosopis, Andrena, &c.). 
7. Other Hymenoptera. 
8. Lepidoptera. 
Arranging these in order of specialization to floral diet, we 
should have first groups 8 and 5, then 6 and 3, and lastly 
7, 4, 2, and 1. 
Tables are given showing the numbers of species of insects 
of each kind that visit the different floral groups, and it is at 
once seen that the bulk of the visitors to the higher types of 
flowers are insects of high degree of specialization, e. g. in the 
Alps, to 100 flowers of class H, the visitors were : — Lepi- 
doptera, 39a per cent. ; long-tongued bees, 48-8 percent.;' and 
all other insects together, 12*1 per cent. On the other hand, 
of the visitors to flowers of class A, the Lepidoptera and 
bees form only 14-2 per cent. 
Loew(292$) observed the visitors to exotic plants in the 
Berlin Botanic Garden, and the results thus obtained were in 
accord with Muller s theory, and gave it great support. Since 
that time many observations have been made in various parts 
1 Class 6 is not usually considered a separate class. 
