*76 HOW TO COLLECT 
size. When the collector remains long enough in one spot, he should 
always endeavour to obtain specimens of a species on different dates, 
in such a way as to throw as much light as possible on the duration 
of its seasonal occurrence. Similarly the attempt should be made to 
illustrate the geographical range or local distribution of a species, 
by collecting specimens in as many different localities as possible. 
Specimens of species taken in new localities, though common else¬ 
where, will always be valuable. 
Larvae and their Habits. 
The habits of Dipterous larvae are as varied as the outward 
appearance of the larvae themselves. The latter may be met with 
almost everywhere, but especially in decaying matter of all kinds, 
in water both running and stagnant, in the ground, attacking the 
roots and bulbs of plants, or mining in the stems and leaves. It is 
worth noting, especially as a means of distinction from Coleopterous 
larvae, that no Dipterous larva is possessed of true (thoracic ) legs , 
though in many species (e.g. Kristalis , Helophilus ) prolegs or trans¬ 
verse ridges having a similar function are distinctly visible. 
The following notes as to the mode of life of the larvae of some of 
the best-known families of Diptera maybe useful:—- 
The tiny pink- or scarlet-coloured grubs of the Gall-midges 
(Cecidomyidce ), as their name implies, form galls on the leaves and 
stems of plants. 
The white grubs of the Fungus-midges (Mjcetophilidue ) have black 
heads, and are to be found for the most part in fungi and boleti. 
The larvae of Bibionidce —a family that in¬ 
cludes “St. Mark’s fly” ( Bibio marci , L.) and 
other species of black flies, which in England 
are exceedingly common in meadows in spring 
and early summer, sometimes hovering in the 
air, dancing in swarms, or feeding on the heads 
of Composite—are similar in appearance, and 
may be met with in vegetable mould, or in the 
droppings of cattle. 
The greenish, somewhat leech-like larvae of the Simulidce— a 
family that includes a number of blood-sucking species—may be 
