Читать книгу Directions for Collecting and Preserving Insects - Charles V. Riley - Страница 11

Table of Contents

The Sweeping Net.—A multitude of insects of all orders feed or rest on grasses and other low plants. Upon close inspection of these plants a careful observer will be able to secure, without any instruments, not only many mature insects, but also many larvæ in connection with their food-plants. This is laborious and slow work, only necessary on special occasions. The beating net, which is constructed on the same general plan as the butterfly net, is valuable here as a time saver. By holding the handle of the net firmly in one hand and quickly sweeping over the plants first from right to left, and then, after quickly turning the net again, sweeping from left to right, most insects coming within reach of the sweep will fall into the bag and may be easily taken out and put into the collecting-vials. From this mode of operation it is evident that the sweeping net must be stronger in all its parts than the butterfly net, but otherwise it may be made on the same plan.

Fig. 47.—The Deyrolle Sweeping Net. a, net entire; b, frame; c and d, attachment of frame and handle (original).

The ring should be rigid, made of brass or iron, either of one piece or of two pieces, and fastened to the handle or stick in the same way as the butterfly net. The bag need not be as long as in the butterfly net, about 18 inches being sufficient, but it should be of stout cotton or linen and the bottom should preferably be sewed in as a round piece, so as to avoid corners. Care needs to be bestowed on the fastening of the bag on the ring, for by the use of the net the part of the bag sewed around the ring is soon chafed through. To prevent this a strip of leather is sewed over the cotton along the rim, but since even this must be frequently renewed some other devices are used to give greater durability to the net. In the pattern of a beating-net originally sold by Deyrolle in Paris, the metal ring was flattened, with the narrow edge pointing upwards and the broad side pierced with holes at suitable intervals and grooved on the outer surface between the holes. The bag is sewed on to the inner side of the ring by stout twine, which passes from one hole to the next and is thus prevented from coming in contact with obstructive objects, and only the bottom of the bag wears and will need to be occasionally mended or renewed.

Fig. 48.—Beating net, opened and attached to handle,

with frame of same folded.

(After Kiesenwetter.)

Another method of preventing the tearing of the upper rim of the bag is described and illustrated in Kiesenwetter's useful volume “Der Naturaliensammler” from which I shall frequently have occasion to quote. In this net the main ring is of rounded iron wire on which a number of brass rings are slipped. These must be but little larger than the diameter of the wire. These little brass rings should not be more than 30 mm. or at most 40 mm., distant from each other, and to them the upper rim of the bag is sewed with very strong twine and is thus protected from wear and tear. The handle or stick of the net should be firmly and solidly attached to the ring and should be stout and not liable to break. I prefer a rather short stick, say not longer than two feet.

I figure herewith the ring of a very convenient net for sweeping or beating purposes. It has the advantage of being for sale on the market, and in fact is an ordinary fishing dip net of small size. It is hinged in three places, as shown in the figure, and folds into very small compass. When unfolded and brought together, it screws into a ferrule which may be attached to a cane or a special handle.

Fig. 49.—Folding ring

for beating net (original).

The beating net can be successfully used at almost every season of the year. Even on warm days in winter time many specimens can be swept from the dead grass. So long as the dew is on the plants or in rainy weather no beating should be attempted, as the more delicate species are more or less spoiled by the moisture. After one or two minutes' sweeping the contents should be examined. Those insects which are quick to take wing or which are good runners should first receive attention; the less active can then be examined more at leisure. The desiderata are then disposed of, the rest thrown away, and the beating renewed.

The beating net is an important instrument for collecting all insects excepting mature Lepidoptera, which are apt to get rubbed. Many larvæ, especially of Lepidoptera, are caught by beating and are mostly in good condition, but it is usually difficult to ascertain the food plant.

Fig. 50.—The Water Net.

(After Packard.)

The Water Net.—The numerous insects or insect larvæ which live in the water can not be conveniently collected without the use of a net, except where they live in small shallow streams or creeks with gravelly or stony bottoms. A suitable water net can readily be made by using the frame of the beating net and attaching to it a rather short bag of some coarse material, e.g., “grass cloth,” coarse millinet. The mode of operation with this net is very simple: if some insect is seen swimming in the water, the net is carefully brought beneath the specimen, which is thus lifted out of the water. Most water insects are, however, not seen swimming about freely, but hide amid the various plants, mosses, etc., or in the mud at the base of the plants, and they can best be captured by dragging the net through these plants. When taken from the water the net is more or less filled with mud and parts of plants, and the water must be allowed to run out and the contents of the net spread out on a cloth or on a flat stone, if such be at hand. The insects are at first not readily seen, but after a short while they begin to emerge from the mud and crawl about, and can readily be taken up with a forceps.

Fig. 51.—Small Water

Dip Net (original).

Water Dip Net.—The small water sieve, shown in the accompanying illustration (Fig. 51), and somewhat resembling in appearance a jockey cap, is frequently of service in collecting the larvæ of aquatic insects, especially where it is necessary to scrape submerged stones or timbers. In use it is fastened on the end of a cane or stick, and can be easily made by any tinsmith.

The Umbrella.—The umbrella, as already stated, is one of the most useful instruments of the collector, since it enables him to obtain all those numerous insects which live on the branches of trees, on shrubs, and on other large plants. A common stout cotton umbrella is sufficiently large, but is liable to get out of joint, and moreover the specimens hide themselves under the ribs. It is well, therefore, to have the inside of such umbrella lined along the ribs with muslin, or some other material, preferably of a light color. An umbrella specially constructed for entomological purposes is offered for sale by E. Deyrolle, in Paris. It resembles a stoutly built common umbrella, but has the inside lined with white linen and the handle has a joint near the middle, so that the umbrella can be more conveniently held and more readily packed away. The opened and inverted umbrella is held with the left hand under the branch which the collector intends to relieve of its entomological inhabitants, while the right hand, armed with a heavy stick, is free to properly jar the branch. Care must be taken in the jarring, lest the insects are knocked beyond the circumference of the umbrella. The larger the umbrella the greater are the chances of making rich captures, but the more difficult it becomes to manipulate, especially where the woods are dense or where there are many vines, etc. In the absence of an umbrella the butterfly net or the beating net can be used.

Fig. 52.—The Umbrella and its mode of use. (After Kiesenwetter.)

A drawback to collecting with the umbrella is that many insects take wing and escape before being secured. This can hardly be avoided, and experienced collectors, in southern countries more particularly, have found it advisable to discard the umbrella and to use in its stead a very large butterfly net, 2 feet or more in diameter.

The Beating Cloth.—A very simple substitute for the umbrella, and one which can always be carried without inconvenience, may here be described. It consists of a piece of common unbleached cotton cloth (1 yard square), to each corner of which a loop of stout twine is sewed. Upon reaching the woods, two straight sticks, each about 5 feet in length and not too heavy, but also not so small as to be liable to break or to bend too easily, are cut from a convenient bush. The sticks are placed crosswise over the cloth and fastened to the loops at the four ends. This is easily and quickly done by making sliding loops of the simple loops. The cloth is thus kept spread out between the sticks, and forms a very good substitute for an umbrella. In beating, the sticks are held at their intersecting points. When not in use one of the loops is detached from the stick and the instrument can be rolled up and carried under one arm without seriously interfering with other operations of the collector. When laid on the ground, with the sticks on the underside, this simple instrument may be advantageously used as a cloth on which to sift or examine fungi, moss, pieces of bark, etc., and since the cloth is always tightly expanded, it offers a smooth and level surface, where examination of various objects can be made with ease and accuracy.

Fig. 53.—The umbrella beating and sweeping net (original).

The Umbrella Net.—A very convenient form of net for both sweeping and for use in place of an umbrella for beating has been devised by Dr. George Marx. (See Fig. 53) It is constructed from an old umbrella, as follows: To the handle of the umbrella are attached two steel rods working on hinges at the apex of the umbrella, as do the ordinary umbrella ribs, and attached to the sliding piece of the umbrella in the same manner, as shown at a. These rods should be about 2½ feet long. When the sliding piece is pushed up and caught behind the spring clip, as shown at b, a circular loop is formed giving the framework for the net. The latter, which should be comparatively shallow, is made of stout muslin and sewed to the frame, as in the ordinary sweeping net. The enlarged drawings c and d illustrate clearly the manner of constructing the frame. The advantage of this net is its convenience in carrying and its general usefulness, taking the place of both the umbrella and the sweeping net. When not in use the frame is allowed to assume the position shown at A, and the net may be wrapped about the frame and the whole inserted in an ordinary umbrella cover.

Fig. 54.—The sieve. a, wire netting (original).

The Sieve.—This useful aid to good collecting has not been generally employed by American entomologists. It facilitates the finding of small insects living under old leaves, in moss, in decayed trees, in fungi, in ants' nests, or in the ground. Any ordinary sieve about a foot in diameter and with meshes of about one-fifth of an inch will answer, though for durability and convenience of carriage one made of two wire or brass rings and muslin (Fig. 54), as follows, is the best. The ends of the wire netting should be bent around the ring so as not to project. A piece of common muslin about 1 foot wide and long enough to go around the circumference of one of the rings is then sewed together so as to form a kind of cylinder or bag without bottom, and the upper and lower rims of this bag are then sewed on around the two rings. The whole instrument thus forms a bag, the top of which is kept open by the simple wire ring, and the bottom is closed by the second ring covered with the wire netting. After choosing a suitable locality a white cloth is spread as evenly as possible on the ground; the collector then takes the sieve, places therein two or three handfuls of the material to be sifted, returns to his cloth, and, holding with his right hand the lower ring and with the left hand the upper ring, shakes the sieve over the cloth. The larger particles and specimens are retained in the sieve while the smaller fall through the meshes on to the cloth. Care must be taken that the siftings form an even and thin layer on the surface of the cloth, so as to be easily examined from time to time. If the locality is favorable many insects will be seen at the first glance crawling or running about, and these can easily be picked up by means of a moistened brush, or with the forceps. Many other insects, however, either feign death or, at any rate, do not move until after the lapse of several minutes, and the proper investigation of a single sifting often requires much time, and patience will be more fully rewarded here than in any other mode of collecting.

The size of the wire meshes given above is best adapted for sifting the fragments of old decayed trees, which furnish the most frequent material for the use of the sieve, but for sifting ants' nests, soil, etc., a sieve with smaller meshes is desirable.

The sieve is indispensable to the Coleopterist, the Arachnologist, and to the specialist in the smaller Hemiptera and Hymenoptera, but it is also useful for most other orders, many interesting species existing which can be secured in numbers only by this mode of collecting. Many Tineidæ and even Noctuidæ hide under old leaves, but the specimens are usually rubbed and rendered useless in the process of sifting. Many larvæ and pupæ can, however, thus be obtained.

If the locality chosen for sifting prove to be a good one, it pays to put the sifted material in a small sack and to carry it home where it can be investigated at leisure, and with a greater thoroughness than is usually possible outdoors. This sack can be easily arranged to be attached to or drawn over the lower ring of the sieve, so that the sifting can be done directly into the sack.

As a rule it may be said that very dry places are least productive, while more or less moist places are apt to furnish a rich harvest. Old wet leaves lying immediately along the edges of swamps, or wet moss, harbor many interesting insects, but such wet material is sifted with difficulty.

The sieve can be used with great advantage at all seasons of the year, but more especially late in fall or early in spring, when so many species are still hibernating.

The Chisel.—For securing the many insects living or hiding under bark of dying or dead trees an instrument of some sort is indispensable, as, in most cases, the bark so firmly adheres to the wood that it cannot be torn off with the hand. A stout pocket-knife will do good service, but far better is a common chisel of medium size and with a short handle. This chisel is also useful as an instrument for digging in the ground or for investigating the interior of partly decayed logs.

The Trowel.—Aside from the fact that many insects enter the ground for the purpose of hibernation in various stages, there is a rich subterranean life to be found during the summer. There are many burrowing Coleoptera; many, if not most, ants construct subterranean nests; the number of other fossorial Hymenoptera is very large, and there are also various burrowing Orthoptera and many Lepidopterous larvæ which hide in the ground during the day. Some instrument for digging in the ground is therefore of great importance, and while, as stated above, the chisel will answer this purpose if nothing else be at hand, yet there are other instruments which perform the work much quicker and more thoroughly. The most available instrument is a rather small steel trowel, such as can be had at the hardware stores in a great variety of patterns, and which can be carried on excursions without much inconvenience. One with a long and narrow blade, made very stout, I have found very useful, though somewhat awkward to carry.