“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 glass 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 pupæ 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.
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 frass 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 glass, 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 Association for the Advancement of Science, August 20, 1890, “there is a great individuality, or rather specificality, in insects, and not infrequently specimens of larvæ 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 larvæ. In many cases such larvæ 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 passed from the ovipositor.” Mr. Fletcher has secured a number of eggs from rare species in this way, and successfully reared the larvæ. The following directions for obtaining the eggs and rearing the larvæ 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 larvæ. 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 butterfly 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 antennæ 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 larvæ or those which it is desired to examine often, glass tubes or jelly glasses 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 shine directly upon them. If moisture gathers inside the glasses the top should be removed for a short time. Larvæ 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, glass 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 larvæ wander very much and climb with the greatest ease over glass, 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 larvæ 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 (Cynipidæ), 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 pupæ or larvæ 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 Microlarvæ and pupæ. 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.