Directions for Collecting and Preserving Insects Part 12

_General Directions._--The importance, even to the mere collector, of rearing insects to obtain specimens for the cabinet has been referred to from time to time in these pages. The philosophic study of entomology, however, requires much more than the mere collecting of specimens, and one of the most profitable and, at the same time, most fascinating phases of the study relates to the life-history and habits. In no branch of natural history are biologic studies more easily carried on, or the biologic facts more remarkable or interesting. The systematist by such study will be saved from the narrow and hair-splitting tendencies which study of slight difference of characters tends to, while to the economic entomologist it is most essential.

In the rearing of insects success will be attained in proportion to the extent to which the conditions of nature in the matters of temperature, moisture, food-supply, and conditions for pupation, are observed.

"In the hands of the careful breeder an insect may be secured against its numerous natural enemies and against vicissitudes of climate, and will, consequently, be more apt to mature than in a state of nature. The breeding of aquatic insects requires aquaria, and is always attended with the difficulty of furnis.h.i.+ng a proper supply of food. The transformations of many others, both aquatic and terrestrial, can be studied only by close and careful outdoor observation. But the great majority of insect larvae may be reared to the perfect state indoors, where their maneuverings may be constantly and conveniently watched. For the feeding of small species, gla.s.s jars and wide-mouthed bottles will be found useful. The mouths should be covered with gauze or old linen, fastened either by thread or rubber, and a few inches of moist earth at the bottom will furnish a retreat for those which enter it to transform and keep the atmosphere in a moist and fit condition.

_The Breeding Cage or Vivarium._--"For larger insects I use a breeding cage or vivarium which answers the purpose admirably. It is represented in figure 123, and comprises three distinct parts: First, the bottom board _a_, consisting of a square piece of inch thick walnut with a rectangular zinc pan _ff_, 4 inches deep, fastened to it above, and with two cross pieces _gg_ below, to prevent cracking or warping, facilitate lifting, and allow the air to pa.s.s underneath the cage. Second, a box _b_ with three gla.s.s sides and a gla.s.s door in front, to fit over the zinc pan. Third, a cap _c_, which fits closely on to the box, and has a top of fine wire gauze. To the center of the zinc pan is soldered a zinc tube _d_ just large enough to contain an ordinary quinine bottle. The zinc pan is filled with clean sifted earth or sand _e_, and the quinine bottle is for the reception of the food plant. The cage admits of abundant light and air, and also of the easy removal of excrement or fra.s.s which falls to the ground; while the insects in transforming enter the ground or attach themselves to the sides or the cap, according to their habits. The most convenient dimensions I find to be 12 inches square and 18 inches high: the cap and the door fit closely by means of rabbets, and the former has a depth of about 4 inches to admit of the largest coc.o.o.n being spun in it without touching the box on which it rests. The zinc pan might be made 6 or 8 inches deep, and the lower half filled with sand, so as to keep the whole moist for a greater length of time."

The sand or earth in the zinc pan at the bottom of the breeding cage should be kept constantly moistened, and in the case of hibernating pupae the constant adding of water to the top of the earth or sand causes it to become very hard and compact. To overcome this objection it was suggested in the _Entomologists' Monthly Magazine_ for June, 1876, page 17, that the base should be made with an inner perforated side, the water to be applied between it and the outer side, and I have for some years employed a similar double-sided base, which answers the purpose admirably (See Figure 124). It is substantially the same as that made for the Department by Prof. J. H. Comstock in 1879. It consists of a zinc tray _a_, of two or three inches greater diameter than the breeding cage, which surrounds the zinc pan proper containing the earth, and the tube _d_ for the reception of the food-plant. The lower portion of the inner pan _b_ is of perforated zinc. Zinc supports, _c c_, are constructed about halfway between the bottom and the top of this pan, on which the breeding cage rests. In moistening the earth in the cage, water is poured into the tray, which enters the soil slowly, through the perforations in the zinc pan. I have found this modification of very decided advantage and use it altogether in the work of the Division, and heartily recommend it.

[Ill.u.s.tration: FIG. 123.--Insect breeding-cage or vivarium.]

The base of the vivarium or breeding cage should never be made of tin, but always of zinc. If made of tin, it will soon rust out. Galvanized iron may be used in place of the zinc, and will doubtless prove equally satisfactory.

"A dozen such cages will furnish room for the annual breeding of a great number of species, as several having different habits and appearance, and which there is no danger of confounding, may be simultaneously fed in the same cage. I number each of the three parts of each cage to prevent misplacement and to facilitate reference, and aside from the notes made in the notebook, it will aid the memory and expedite matters to keep a short open record of the species contained in each cage, by means of slips of paper pasted on the gla.s.s door. As fast as the different specimens complete their transformations and are taken from the cage the notes may be altered or erased, or the slips wetted and removed entirely. To prevent possible confounding of the different species which enter the ground, it is well, from time to time, to sift the earth, separate the pupae and place them in what I call 'imago cages,' used for this purpose alone and not for feeding. Here they may be arranged with references to their exact whereabouts.

[Ill.u.s.tration: FIG. 124.--Improved base for breeding-cage (original).]

"A continued supply of fresh food must be given to those insects which are feeding, and a bit of moist sponge thrust into the mouth of the bottle will prevent drowning, and furnish moisture to such as need it.

By means of a broad paste brush and spoon the fra.s.s may be daily removed from the earth, which should be kept in a fit and moist condition--neither too wet nor too dry. In the winter, when insect life is dormant, the earth may be covered with a layer of clean moss, and the cages put away in the cellar, where they will need only occasional inspection, but where the moss must nevertheless be kept damp. Cages made after the same plan, but with the sides of wire gauze instead of gla.s.s, may be used for insects which do not well bear confinement indoors, the cages to be placed on a platform on the north side of a house, where they will receive only the early morning and late evening sun."

_Detailed Instructions for Rearing._--In the rearing of insects every worker will develop a number of methods of value, and it is only by careful study and comparison of the experiences of all that the best system can be elaborated. For this reason I have, in what follows, quoted, in a more or less fragmentary way, the experiences of different entomologists.

As is remarked by Miss Murtfeldt, in an interesting paper read before the Entomological Club of the American a.s.sociation for the Advancement of Science, August 20, 1890, "there is a great individuality, or rather specificality, in insects, and not infrequently specimens of larvae are found for which the collector taxes his ingenuity in vain to provide.

Not the freshest leaves, the cleanest swept earth, or the most well-aired cages will seem to promote their development."

The greatest care and watchfulness, therefore, are necessary to insure success in the rearing of larvae. In many cases such larvae can only be successfully reared by inclosing them in netting on their food-plant out of doors. It is a frequent device of Lepidopterists also to inclose a rare female in netting placed on the food plant of the species, where the male may be attracted and may be caught and placed in the bag with the female, when copulation usually takes place successfully, or a male may be caught in the field and inclosed with such female. Mr. W. H.

Edwards, where the plant is a small one, uses for this purpose a headless keg covered at one end with gauze, which he places over the plant inclosing the female.

Mr. James Fletcher, of Ottawa, Canada, one of our most enthusiastic rearers of insects, has given some details of his methods in a recent very interesting account of "A Trip to Nepigon." One style of cage used by him in securing the eggs of large Lepidoptera "is made by cutting two flexible twigs from the willow or any other shrub and bending them into the shape of two arches, which are put one over the other at right angles and the ends pushed into the ground. Over the penthouse thus formed a piece of gauze is placed, and the cage is complete. The edges of the gauze may be kept down either with pegs or with earth placed upon them." This kind of cage is used for all the larger species which lay upon low plants. The species which oviposit on larger plants or trees are inclosed in a gauze bag tied over the branch. This is applicable to insects like _Papilio_, _Limenitis_, _Grapta_, etc. Care must be taken, however, that the leaves of the plant inside the net are in a natural position, for some species are very particular about where they lay their eggs, some ovipositing on the top of the leaves, others near the tip, and many others on the under surface. "When a bag made beforehand is used, the points must be rounded, and in tying the piece of gauze over the branch care must be taken to pull out all creases and folds, or the insect will be sure to get into them and either die or be killed by spiders from the outside of the bag. It is better to put more than one female in the same cage. I have frequently noticed that one specimen alone is apt to crawl about and settle on the top of the cage, and not go near the food plant. When there are two or three they disturb each other and are frequently moving and falling on the food plant, when they will stop for a moment and lay an egg. A stubborn female of _Coleus eurytheme_ was only induced to lay by having a male placed in the cage with her, and by his impatient fluttering and efforts to escape she was frequently knocked down from the top, and every time she fell upon the clover plant beneath, she laid an egg before crawling to the top again."

Some insects, even with all care in making their surroundings as natural as possible, will persistently refuse to lay. Mr. Fletcher has successfully obtained eggs from some of these by a method which he says one of his correspondents styles "Egg-laying extraordinary." It consists simply in "gently pressing the abdomen of a female which has died without laying eggs, until one and sometimes two perfect eggs are pa.s.sed from the ovipositor." Mr. Fletcher has secured a number of eggs from rare species in this way, and successfully reared the larvae. The following directions for obtaining the eggs and rearing the larvae of Lepidoptera, given in this paper by Mr. Fletcher, are excellent, and I quote them entire:

"There are one or two points which should be remembered when obtaining eggs and rearing larvae. In the first place, the females should not be left exposed to the direct rays of the sun; but it will be found sometimes that if a b.u.t.terfly is sluggish, putting her in the sun for a short time will revive her and make her lay eggs. Confined females, whether over branches or potted plants, should always be in the open air. If females do not lay in two or three days they must be fed. This is easily done. Take them from the cage and hold near them a piece of sponge (or, Mr. Edwards suggests, evaporated apple), saturated with a weak solution of sugar and water. As soon as it is placed near them they will generally move their antennae towards it, and, uncoiling their tongues, suck up the liquid. If they take no notice of it the tongue can be gently uncoiled with the tip of a pin, when they will nearly always begin to feed. It is better to feed them away from the plant they are wanted to lay upon, for if any of the sirup be spilled over the flowerpot or plant it is almost sure to attract ants. I kept one female _Colias interior_ in this way for ten days before eggs were laid. When eggs are laid they should, as a rule, be collected at short intervals.

They are subject to the attacks of various enemies--spiders, ants, crickets, and minute hymenopterous parasites. They may be kept easily in small boxes, but do better if not kept in too hot or dry a place. When the young caterpillars hatch they must be removed with great care to the food plant; a fine paint brush is the most convenient instrument. With small larvae or those which it is desired to examine often, gla.s.s tubes or jelly gla.s.ses with a tight-fitting tin cover are best. These must be tightly closed and in a cool place. Light is not at all necessary, and the sun should never be allowed to s.h.i.+ne directly upon them. If moisture gathers inside the gla.s.ses the top should be removed for a short time. Larvae may also be placed upon growing plants. These can be planted in flowerpots and the young caterpillars kept from wandering either by a cage of wire netting or, by what I have found very satisfactory, gla.s.s lamp chimneys. These can be placed over the plant, with the bottom pushed into the earth, and then should have a loose wad of cotton batting in the top. This has the double effect of preventing too great evaporation of moisture and keeping its occupants within bounds. Some larvae wander very much and climb with the greatest ease over gla.s.s, spinning a silken path for themselves as they go. When caterpillars are bred in the study it must not be forgotten that the air inside a house is much drier than it is out of doors amongst the trees and low herbage, where caterpillars live naturally. The amateur will require some experience in keeping the air at a right degree of moisture when breeding upon growing plants. In close tin boxes or jars, where the leaves must be changed every day, there is not so much trouble. An important thing to remember with larvae in jars is to thoroughly wash out the jars with cold water every day. If, however, a caterpillar has spun a web on the side and is hung up to moult, it must not be disturbed. In changing the food it is better not to remove the caterpillars from the old food, but having placed a new supply in the jar, cut off the piece of leaf upon which they are and drop it into the jar. If they are not near the moult a little puff of breath will generally dislodge them.

Some caterpillars, as _Papilio turnus_, which spins a platform to which it retires after feeding, can best be fed upon a living tree out of doors, but must be covered with a gauze bag to keep off enemies. A piece of paper should be kept _attached_ to each breeding jar or cage, upon which regular notes must be taken _at the time_, giving the dates of every noticeable feature, particularly the dates of the moults and the changes which take place in the form and color at that time."

The necessity of outdoor work is further felt in the determination of the facts in the life-history of some insects which have an alternation of generations, as some Gall-flies (_Cynipidae_), and most Aphides. To successfully study these insects constant outdoor observation is necessary, or the species must be inclosed in screens of wire or netting outdoors on their food-plant. Many insects which breed on the ground or on low herbage may be very successfully watched and controlled by covering the soil containing them or the plant on which they feed with a wire screen or netting. The use of wire screens is also advisable in the case of wintering pupae or larvae out of doors. Many species can be more easily carried through the winter by placing them outdoors under such screens during the winter, which insures their being subjected to the natural conditions of climate, and then transferring them to the breeding cage again early in the spring. This is advisable in the case of Microlarvae and pupae. Species which bore in the stems of plants may be easily cared for and leaf-mining and leaf-webbing forms can be secured under screens or covers out of doors for the winter in sheltered situations. Many species which, if kept in a warm room can not be reared, will, if subjected to freezing weather under slight protection in the open air, emerge successfully the following spring.

The greatest care is necessary in the breeding of Tenthredinidae, as most of them transform under ground and are single brooded, the larvae remaining in the ground from midsummer until the following spring.

Nothing but constant care in maintaining uniform moisture and temperature of the soil will insure the success of such breeding. Some species bore into rotten wood or the stems of plants to undergo their transformations, as for instance the Dogwood Saw-fly (_Harpiphorus varia.n.u.s_). This species, unless supplied with soft or rotten wood in which to bore, will wander ceaselessly round the cage, and in most cases eventually perish.

Where a small room can be devoted to the purpose, an excellent wholesale method of obtaining wood-boring insects (_Coleoptera_, _Lepidoptera_, etc.) is to collect large quant.i.ties of dead or dying wood of all sorts or any that indicates the presence of the early states of insects, and store it in such apartment. The following spring and summer the escaping insects will be attracted to the windows and may be easily secured. The objection to this method is that, in many cases, it will be impossible to determine the food habit of the insect secured, owing to the variety of material brought together.

_The Root Cage._--For the study of insects which affect the roots of plants a root cage has been devised by Prof. J. H. Comstock which is of sufficient importance to warrant full description. It consists of a zinc frame (Fig. 125_a_) holding two plates of gla.s.s in a vertical position and only a short distance apart, the s.p.a.ce between the plates being filled with soil in which seeds are planted or small plants set. Outside of each gla.s.s is a piece of zinc or sheet iron (_b_) which slips into grooves and which can be easily removed. When these zincs are in place the soil is kept dark.

The idea of the cages is, that the s.p.a.ce between the gla.s.ses being very narrow, a large part of the roots will ramify close to the surface of the gla.s.s, so that by removing the zinc slides the roots may be easily seen, and any root-inhabiting insects which it maybe desirable to breed may thus be studied in their natural conditions without disturbing them.

Prof. Comstock has used this cage very successfully in studying the habits of wire-worms, and its availability for many of the underground insects, such as the Cicadas, root-lice, larvae, etc., is apparent. These frames may be made of various sizes, to accommodate particular insects.

It will be of advantage in many cases, in order to secure the natural conditions as nearly as possible, to sink the cage in the soil, and for this purpose Prof. Comstock has had constructed a pit lined with brick for the reception of his cages, and employs a small portable crane to lift them out of the ground when it is desirable to examine them.

_Other Apparatus._--Much of the breeding of insects can be done with the simplest apparatus, and for the rearing of Microlepidoptera, Gall-insects, and the keeping of coc.o.o.ns and chrysalides of small species, nothing is more convenient than a medium sized test-tube, the end of which may be plugged with cotton. I have recently successfully carried over the winter the larva of _Sphecius speciosus_, which had been removed early in the fall from its earthen pod or coc.o.o.n, the larva transforming to a perfect pupa in the spring. In this case the test tube was plugged with cotton and inserted in a wooden mailing tube to exclude the light. Smaller jars with gla.s.s covers or with a covering of gauze may be employed for most insects, with the advantage of occupying comparatively little s.p.a.ce and of isolating the species under study.

[Ill.u.s.tration: FIG. 125.--Root cage: _a_, frame with slide removed; _b_, movable slide; _c_, top view (original).]

Long gla.s.s tubes, open at both ends, are useful in many other ways, especially in the rearing and study of the smaller hypogean insects or those which bore and live in the stems of plants. An infested stem cut open on one side and placed in such a tube will generally carry any insect that has ceased feeding, or any species like the wood-boring bees which feed upon stored food, successfully through their transformations; while root-lice may be kept for a lengthy period upon the roots in such tube, providing a portion of the root extends outside of the tube and is kept in moistened ground or water. In all such cases these tubes, with their contents, should be kept in the dark, either in a drawer or else covered with some dark material which can be wound around or slipped over them, and the ends must be closed with cotton or cork.

The rearer of insects will frequently experience difficulty in carrying his pupae through the winter, and, even though ordinary precautions are taken, the mortality will frequently amount to 50 per cent of the specimens. Mr. H. Bakhaus, of Leipzig, thus describes a device which is substantially the base of the vivarium shown on page 114.

"The base consists of a round plate of strong zinc, with two vertical rims, an inch high, placed one within the other, an inch apart, and soldered to the basal plate so that the outer one is water-tight. The inner rim must be perforated with small holes as close to the bottom as possible. The s.p.a.ce inside the inner rim must be filled with fine sand, on which the pupae should be laid. The s.p.a.ce between the two rims is then filled with water, which, finding its way through the holes in the inner rim to the sand, causes the necessary moisture. Over the whole is put a bell-shaped cover of wire gauze, which must fit tightly over the outer rim. In this receptacle the pupae remain untouched, and receive fresh moisture, as above indicated, if required by the drying of the sand."

The hardy pupae of most Noctuids and Bombycids, as well as those of many Rophalocera, may be handled with little danger, but other species, if handled at all, or if the coc.o.o.ns which they make for themselves are broken, can seldom be reared. Constant precautions also must be exercised in the care of the soil and the breeding cages. One of the great drawbacks is the presence of mites and thread worms (Entozoons), etc., which affect dying or dead pupae and larvae in the soil. They also affect living specimens and are capable of doing very considerable damage. To free the soil of them it is necessary at times to allow the earth to become dry enough to be sifted, and then after removing the pupae submit it to heat sufficient to destroy any undesired life there may be in it.

_The Insectary._--Up to the present time the work of rearing insects has been largely confined to the breeding cage and breeding jar, already described, which have been kept in the rooms of the investigator. The advantages of having a special building for this purpose are at once apparent and need not be insisted upon. One of the best establishments of this kind is that of the Cornell University Experiment Station, which was fully described in Bulletin No. 3, of that station, November, 1888.

The Kansas Experiment Station has a similar building, and one has recently been built for the use of the Entomological Division of the United States Department of Agriculture. The insect-breeding house, or insectary, should comprise a building having workrooms, or laboratories, for microscopic and general work in the study and preparation of specimens, and also a conservatory for the rearing of specimens and the growth of plants, and, where applied entomology is concerned, special rooms for the preparation and the test of insecticides. The building proper should also have a bas.e.m.e.nt storage room for hibernating insects.

The laboratory should be fitted with all the apparatus used in the study of insects, including microscopes and accessories and a dark-room for photographic purposes.

DIRECTIONS FOR TRANSMITTING INSECTS.

It is very desirable in transmitting insects from the field of exploration, or from one entomologist to another, for information, exchange, or other purpose, that they be properly secured and packed.

Pinned and mounted specimens should be firmly fixed in a cigar box, or a special box for mailing, and this should be carefully but not too tightly wrapped with cotton or other loose packing material to a depth of perhaps an inch, and the whole then inclosed in stiff wrapping paper.

It is preferable, however, to inclose the box containing the specimens in a larger box, filling the intervening s.p.a.ce, not too firmly, with cotton or other packing material. Where specimens are to be sent to a considerable distance it is advisable also to line the box in which they are placed with cotton, which serves to catch and hold any specimens which may become loose in transit. In the case of alcoholic specimens each vial should be wrapped separately in cotton and placed in a strong wooden or tin box. Special mailing boxes for alcoholic specimens have been devised, and a very convenient form is herewith figured. It is an ordinary tube of wood, with a metal screw top, and the interior lined with rough cork. These tubes are made in various sizes to accommodate vials of different dimensions.

[Ill.u.s.tration: FIG. 126.--Wooden-tube mailing-box: _a_, tube; _b_, cover (original.)]

In mailing living specimens the essential thing is a strong box, preferably tin, made as nearly air-tight as possible. I have found it very convenient on long trips to carry with me a number of tin boxes in the flat (Fig. 127), combined in convenient packages, ready to be bent and improvised in the field. For this purpose get any tinsmith to make out of good tin a number of pieces cut of the requisite dimensions both for the bottoms and the covers, carefully cutting the corners to permit the proper bending of the sides. These improvised boxes will prove useful for keeping living larvae with their food-plants, especially if tied up in stout brown paper to prevent any exit from the unsoldered angles. They will also answer admirably for mailing or otherwise sending specimens to their ultimate destination. In the case of larvae a quant.i.ty of the food-plant should always be inclosed in the box.

[Ill.u.s.tration: FIG. 127.--Tin mailing-box in the flat: _a_, box; _b_, cover (original).]

In transmitting insects for information the greatest care should be taken to relieve the person of whom information is sought of as much unnecessary work as possible. It is easy for any beginner to collect more in a single day than an experienced entomologist can well mount, study, and determine in a week, and as those who have the means and information to give determinations or otherwise to a.s.sist beginners are generally very much occupied, and their time is valuable, they are justified in ignoring miscellaneous collectings where the sender has made no effort to either properly mount or otherwise study and care for his specimens.

[Ill.u.s.tration: FIG. 128.--Tin mailing-box, bent into shape for use (original.)]

Living specimens, especially larvae, should be packed in tin, with a supply of their appropriate food. The tighter the box the fresher will the food as well as the specimens keep. Insects do not easily suffocate, and it is worse than useless, in the majority of cases, to punch air-holes in such boxes. Dead specimens, when not pinned, may be sent in a variety of ways. Small ones may be dropped into a quill and inclosed in a letter, or a small vial fitted into a piece of bored wood. Those which do not spoil by wetting may be sent in alcohol, provided the bottle is absolutely filled, or, what is better, in sawdust moistened with alcohol, or between layers of cotton saturated with alcohol.

The postal regulations permit the sending by mail of "dried insects * * * when properly put up, so as not to injure the persons of those handling the mails, nor soil the mail bags or their contents." Specimens in alcohol may also be sent by mail, provided that the containing vial be strong enough to resist the shock of handling in the mail, and that it be inclosed in a wooden or papier-mache tube not less than three-sixteenths of an inch thick in the thinnest part, lined with cork or other soft material, and with a screw top so adjusted as to prevent the leakage of the contents in case of breakage. Entomological specimens are of the fourth cla.s.s of mail matter, the postage on which is 1 cent an ounce or fraction thereof, the limit of weight for a single package being 4 pounds, and the limit as to bulk 18 inches in any direction.

Saleable matter is also non-mailable at fourth-cla.s.s rates; so that the safer method, with small packages, is to send under letter postage. It is far better, however, for long journeys, and especially for transatlantic s.h.i.+pment, to send by express.

NOTES AND MEMORANDA.

In the foregoing pages are given some of the more useful directions for those wis.h.i.+ng to commence to collect and study insects. Experience will soon teach many other important facts not mentioned here, and the best closing advice I can give the novice is, to get acquainted, if possible, with some one who has already had large experience. He will be very apt to find such a person pleasant and instructive company whether in the field or in the closet. One important habit, however, I wish to strongly inculcate and emphasize: The collector should never be without his memorandum or note book. More profitless work can scarcely be imagined than collecting natural-history specimens without some specific aim or object. Every observation made should be carefully recorded, and the date of capture, locality, and food-plant should always be attached to the specimens when these are mounted. More extended notes may be made in a field memorandum book carried in the pocket or in larger record books at home. For field memoranda I advise the use of a stylographic pen, as pencil is apt to rub and efface in time by the motions of the body. The larger record book is especially necessary for biologic notes. Notes on adolescent states which it is intended to rear to the imago can not be too carefully made or in too much detail. The relative size, details of ornamentation and structure, dates of moulting or transformation from one state to another--indeed, everything that pertains to the biography of the species--should be noted down, and little or nothing trusted to mere memory where exact data are so essential. Many insects, particularly dragon-flies, have brilliant coloring when fresh from the pupa, which is largely lost afterward. The time of laying and hatching of eggs, the number from a single female, the character of the eggs, general habits, records of parasites and their mode of attack--all should be entered as observed. A great many species have the most curious life histories, which can not be ascertained except by continued and persevering observation, not only in the vivarium or insectary but in the field. It is almost impossible to follow, under artificial conditions, the full life cycle of many species like the Aphididae, or the Gall-flies, etc., which involve alternation of generations, dimorphism, heteromorphism, migration from one plant to another, and various other curious departures from the normal mode of development, without careful field study and experiment. These studies are possible only to those who are able to frequent the same localities throughout the whole year, and can hardly be carried on by the traveling naturalist or collector.