Another splendid method of securing larvæ where mere searching would be tedious and unproductive, lies in the use of the sweep net described on [page 102]. This implement comes into service in waste places that are covered with rank vegetation, in clover and hayfields, and in all spots covered with low herbs.
Walking among the vegetation, the net is swept right and left before you, and the contents examined at frequent intervals. It is advisable to work the different species of herbs separately as far as possible, otherwise there may be some difficulty in the determination of the food plants of the mixed larvæ that the net will contain. If, however, this plan is impracticable, you may save time by turning out all the 'sweepings' into one large box, leaving the sorting to be done at home in leisure hours.
Collecting Pupæ
We have seen that ova and larvæ may be obtained in greater or less abundance at all times of the year, so variable are the seasons of the different butterflies and moths. The same remark applies equally well to pupæ; but so many of the Lepidoptera spend the winter months in the chrysalis state that this period may be regarded as the harvest time of the pupa hunter.
A large number of caterpillars undergo their change to the quiescent state during the months of August and September, and, of course, remain in this state until the warm days of the following spring or summer. And as insects even in the pupal stage have a number of enemies and dangers to contend with, it is advisable to start your search for them as soon as possible after they have changed.
If you set your mind on searching for particular species, you should endeavour to ascertain the usual time at which such species pupate; make any necessary allowances for the forwardness or backwardness of the season, and then allow a week or two for the change to be completed, for insects should never be disturbed at times when their metamorphoses are in progress.
For general pupa hunting the best season is undoubtedly from the end of August to the end of October, but there is no reason why the work should not be carried on throughout the winter. If, however, you continue your work so late, you must not expect
nearly as much success as time advances. You must remember that entomologists are not the only pupa hunters. Many hungry birds are always on the look-out for insects, and seem to enjoy them equally well in all their stages. Those that hybernate on or under the ground are liable to fall a prey to moles and beetles. In addition to these dangers, all pupæ are subject to the effects of extreme cold, dampness, or floods.
As regards the choice of a day, very little need be said. Any day that is sufficiently genial for yourself will do for your work, except that periods of hard frost render the ground too hard for digging—the most profitable part of the pupa hunter's task.
The apparatus required is extremely simple: A satchel or large pockets full of small metal or chip boxes, a small garden trowel, and a strong chisel.