The Gall-flies, Cynipidæ, are the easiest of the families to collect, because of their abundance and because of the ease with which they may be reared. Their galls occur in enormous variety on oaks of various species and also upon brambles and certain common weeds. These should be collected when mature and be kept in glass jars. The Gall-flies and inquilinous and parasitic species may thus be easily obtained, the former appearing at particular seasons and the latter emerging from the galls at all seasons of the year, and sometimes continuing to escape for a period exceeding two years.
Fig. 61.—An Ichneumon (Ophion).
One of the most interesting families in this order is the Formicidæ, which comprises the true ants. In the case of these insects isolated specimens should not ordinarily be collected, and it is especially desirable to collect the species from colonies so that the three forms (males, females, and workers) may be obtained together. This holds also in the case of the social wasps and bees, but the different sexes of the latter may be collected in a season's collecting about flowers, the females and workers in early spring and the males in the fall.
The Uroceridæ or woodborers are to be found only about trees in which the larvæ breed. They may frequently be taken about tree trunks, or burrowing with their long gimlet-like ovipositors into the trunks of trees to oviposit. Breeding is also a satisfactory method of obtaining these insects.
Some special methods of collecting Hymenoptera may be briefly outlined. In the case of the social bees, particularly bumble-bees, and also the smaller wasps and yellow-jackets, a very satisfactory method of collecting consists in first stupefying the insects in the nest by introducing a small amount of chloroform, benzine, or bisulphide of carbon. This should preferably be done in the late evening, after all the insects have come in for the night. The nest may then be opened and examined without any danger of being stung, and the different forms may thus easily be obtained, together with any rare parasitic or inquilinous insects. In the case of the nests of Bombi this is the best method of obtaining the inquilinous Apathus species.
Fig. 62.—The Little Red Ant (Monomorium pharaonis).
a, female; b, worker enlarged.
On account of the danger of being stung, and also on account of the extremely quick flight of these insects, the removing of Hymenoptera from the net is not always an easy task, and in many cases rare specimens escape. One method of avoiding the danger of being stung is to have the collecting net constructed with an opening at the bottom which, during the sweeping, is tied with a string. When a sufficient quantity of insects is obtained they are, by a few quick motions, driven to the bottom of the net, and the net is then seized just above the insects with the hand, the folds of cloth preventing the insects from getting to the hand, so that there is little danger of being stung. The lower end is then carefully untied and inserted into a wide-mouthed bottle, and the contents of the net shaken out into the bottle. After the catch is stupefied the vial may be turned out and the undesirable material discarded. A second method consists in the use of an ordinary sweeping-net of light material. A quantity of Hymenoptera are collected from flowers and driven to the bottom of the net, and secured as in the preceding method. The portion of the net containing the insects is then, by means of a pair of forceps, thrust bodily into a large collecting bottle. After a few minutes the insects are stupefied and may be readily examined.