Most Diptera frequent flowers and may be collected with a sweeping net without much difficulty. The best season is from April to June, and the bloom of the Willow, Alder, Plum, Cherry, Dogwood, Blackberry, etc., will ordinarily yield a bountiful supply of specimens and species. Parasitic and saprophytic forms may also readily be obtained by breeding, the former as in the case of the parasitic Hymenoptera, and the latter from decaying vegetable matter and fungi. The Diptera require the most delicate treatment, and the greatest care must be exercised both in collecting and handling. A light sweep net is the best implement for collecting and the contents of the net should frequently be emptied into bottles provided with blotting paper to absorb the excess of moisture. Very small Diptera should not be killed when they can not be immediately pinned, and hairy flies should never be taken from the net with the hand, but should be handled with fine forceps. A pair of special collecting shears has been used by Lord Walsingham very successfully. It is represented in the accompanying figure, and consists of a pair of screen-covered disks, between which the fly is caught. The insect is at once pinned through the screen and may be removed and transferred to a box containing a sponge soaked in chloroform. The use of this implement is especially advisable in the case of the Bee-flies (_Bombiliidae_) and other hairy forms which are liable to be rubbed when collected in the ordinary net. The Gall-making Diptera (_Cecidomyidae_) are of little value unless accompanied with their galls, and the aim should always be to collect the galls and rear the insects rather than the keeping of specimens taken in the course of general collecting with a sweep net. The rearing of Cecidomyidae is, however, a delicate task, and requires considerable experience. Some knowledge of the habits of the species is very essential to success. From immature galls no rearings need be expected. A good plan is to examine the galls from time to time and collect them when it is found that the larvae are beginning to abandon them. In the case of species like the common Cone Gall-gnat of the Willow, the larvae of which do not leave the gall to undergo transformation in the earth, it is advisable not to gather the galls until the transformation to the pupa state takes place, which, in this species, occurs in early spring. The various leaf-mining and seed inhabiting species can be treated as in the case of the Microlepidoptera. [Illustration: FIG. 81.--A Syrphus-fly.] COLLECTING ORTHOPTERA. [Illustration: FIG. 82.--A blind Cricket (_Hadenalcus_) from Mammoth Cave. (From Packard.)]