^6 HOW TO COLLECl^ 



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. 



Larv^ 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 

 larvjie, that no Dij)terous larva is possessed of true [thoracic) legs, 

 though in many species (e.g. Eristalis, Heloj)hilus) 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 may be 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 {Mycetophilidm) have black 

 heads, and are to be found for the most part in fungi and boleti. 



The larvae of Bibioyiidai — 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 Compositae — are similar in appearance, and 

 WITH HEAD OF 3 ' miij bo mct with in vegetable mould, or in the 



droppings of cattle. 

 The greenish, somewhat leech-like larvae of the Simulidoi — a 

 family that includes a number of blood-sucking species — may be 



