INSECT-POLLINATION OR ENTOMOPHILY 87 
Insect=PoIlination or Entomophily is found in a 
majority of flowers, and adaptation to it has apparently been 
very important in the evolution of most of the higher groups. 
The evolution of the insects apparently went hand-in-hand 
with that of the flowers and it is best to deal with both to- 
gether. The highest types of flower on the whole are suited 
to the highest types of insect, but lower types of both exist 
in profusion. Hermann Muller has divided flowers into a 
number of classes according to their degrees of specialisa- 
tion in this respect. Anemophilous flowers are grouped 
together in a class W, while entomophilous flowers are 
mainly placed in seven other classes, Po, A, AB, B, B', F, 
H, considered below. 
The insects which visit flowers belong to various groups, of which 
the most important are : 
(1) Heiniptera (bugs, &c.) : no special adaptations to floral diet; few 
flower-visiting species. 
(2) Coleoptera (beetles) : many flower-visiting species. The beetles 
are as a rule only able to lick freely-exposed honey, their tongues being 
very short ; a few have tongues 3 to 6 mm. long. The commonest flower- 
visiting genus in Britain is the small bronze-black Meligethes. 
(3) Diptera (flies) : very numerous flower-visiting species. The 
mouth-parts are often highly modified for feeding on honey and pollen. 
For our purpose we may divide the flies into long-tongued and short- 
tongued. The former include the Syrphidae (drone- or hover-flies) and 
a few others, the latter all the remaining forms. The former confine 
themselves to a floral diet and are clever in finding concealed honey ; 
their tongues vary in length from 4 to 12 mm. Many flowers are 
specially adapted to, and visited by, them. The most common genera 
in Britain are Eristalis, Platychirus, Syrphus, Rhingia, &c. The short- 
tongued flies are much less highly adapted to floral diet ; many feed 
also on carrion, &c. (some flowers, e.g. Arum, Rafflesia, Stapelia, &c., 
avail themselves of this habit by a carrion-like smell) ; their tongues are 
short (less than 4 mm.) and they are rarely skilful in finding concealed 
honey. The commonest flower-visiting genera in Britain are Lucilia 
(small blue-bottle), Anthomyia, Scatophaga (dung-fly), &c. 
(4) Hymenoptera (ants, sawflies, ichneumons, bees, wasps, &c.) : 
mostly flower-visiting species. They are all short-tongued except the 
bees, which are the most important group of insects in relation to the 
evolution of flowers. They collect both pollen and honey ; the former 
is usually carried in the brushes of hairs on the hind-legs, into which 
it is brushed by the hairs on the tarsi. We may divide bees, for our 
purposes, into short- and long-tongued, according as the tongue is 
shorter or longer than 6 mm. To the former group belong such small 
bees as Halictus, Andrena, &c. ; to the latter chiefly the hive-bee (Apis) 
and the humble-bee (Bombus). There are a great number of flowers 
adapted to pollination by bees, especially the long-tongued forms. 
