Directions for Collecting and Preserving Insects Part 1

Directions for Collecting and Preserving Insects.

by C. V. Riley.

INTRODUCTORY.

There is a constant demand, especially from correspondents of the Museum and also of the Department of Agriculture, for information as to how to collect, preserve, and mount insects. There is also great need of some simple directions on a great many other points connected with the proper packing of insects for transmission through the mails or otherwise; labeling; methods of rearing; boxes and cabinets; text-books, etc.

Interest in the subject of entomology has, in fact, made rapid growth in the last few years, and now that nearly every State has an official entomologist connected with its State Agricultural Experiment Station, the number of persons interested in the subject may be expected to increase largely in the near future. I have hitherto made use of the Smithsonian Miscellaneous Collections, No. 261, which is a pamphlet on collecting and preserving insects prepared by Dr. A. S. Packard. This is out of print, and I have been requested by Prof. Goode to prepare for Bulletin 39, U. S. N. M., something that would cover the whole ground and give the more essential information needed for collectors and students of insect life. I have deemed it unnecessary to go too much into detail, but have studied not to omit anything essential. Customs and methods vary in different countries and with different individuals, but the recommendations contained in the following pages are based upon my own experience and that of my a.s.sistants and many acquaintances, and embrace the methods which the large majority of American entomologists have found most satisfactory.

Much of the matter is repeated bodily from the directions for collecting and preserving insects published in my Fifth Report on the Insects of Missouri (1872) and quotations not otherwise credited are from that Report. The ill.u.s.trations, also, when not otherwise credited or not originally made for this paper, are from my previous writings. Some are taken from Dr. Packard's pamphlet, already mentioned; others, with the permission of a.s.sistant Secretary Willits, from the publications of the Department of Agriculture, while a number have been especially made for the occasion, either from photographs, or from drawings by Miss L.

Sullivan or Dr. Geo. Marx or Mr. C. L. Marlatt. When enlarged, the natural size is indicated in hair-line. In the preparation of the pamphlet I have had the a.s.sistance of Mr. E. A. Schwarz, and more particularly of Mr. C. L. Marlatt, to both of whom I desire here to express my obligations.

C. V. R.

[Ill.u.s.tration: Pl. 1.--ILl.u.s.tRATION OF BIOLOGIC SERIES.]

MANUAL OF INSTRUCTIONS FOR COLLECTING AND PRESERVING INSECTS.

By C. V. RILEY, _Honorary Curator of the Department of Insects, U. S. National Museum._

CHARACTERISTICS OF INSECTS.

The term "insect" comes from the Latin _insectum_, and signifies "cut into." It expresses one of the prime characteristics of this cla.s.s of animals, namely, that of segmentation. This feature of having the body divided into rings or segments by transverse incisions is possessed by other large groups of animals, and was considered of sufficient importance by Cuvier to lead him, in his system of cla.s.sification, to group with Insects, under the general term Articulata, Worms, Crustacea, Spiders, and Myriapods. Worms differ from the other four groups in having no articulated appendages, and in having a soft body-wall or integument instead of a dense chitinous covering, and are separated as a special cla.s.s _Vermes_. The other four groups of segmented animals possess in common the feature of jointed appendages and a covering of chitinous plates, and are brought together under the term _Arthropoda_.

The division of the body into a series of segments by transverse incisions, characteristic of these animals and these only, justifies the use of Cuvier's old name, Articulates, as this segmented feature represents a definite relations.h.i.+p and a natural division--as much so as the vertebral column in Vertebrates. The Cuvierian name should be retained as a coordinate of Vertebrates, Molluscs, etc., and the terms Vermes and Arthropods may be conveniently used to designate the two natural divisions of the Articulates.

The term "insect" has been employed by authors in two different senses--one to apply to the tracheated animals or those that breathe through a system of air tubes (tracheae), comprising Spiders, Myriapods, and insects proper or Hexapods,[1] and the other in its restricted sense as applied to the Hexapods only. To avoid confusion, the latter signification only should be used, and it will be thus used in this article.

[1] From the Greek [Greek: exapous], having 6 feet.

We see, then, that insects share, in common with many other animals, the jointed or articulated structure. Wherein, then, do they differ?

_Briefly, in having the body divided into thirteen joints and a subjoint_, including the head as a joint, and in the adult having six true, jointed legs, and usually, though not always, wings. The five cla.s.ses of Articulates differ from each other in the number of legs they possess in the adult form, as follows: Hexapoda, 6 legs; Arachnida, 8 legs; Crustacea, 10-14 legs; Myriapoda, more than 14 legs; Vermes, none.

This system holds for the adult form only, because some mites (Arachnida) when young have only 6 legs, and many true insects in the larva state either have no legs at all, or have additional abdominal legs which are not jointed, but membranous, and are lost in the perfect or adult state. These are called false or prolegs.

It will serve to make these instructions clear if I at once explain that the life of an insect is marked by four distinct states, viz., the egg, the larva, the pupa, and the imago, and that the last three words will constantly recur. We have no English equivalent for the words larva and pupa, for while some authors have written them with the terminal _e_, so as to get the English plural, yet "larves" and "pupes" so shock the ear that the terms have not been (and deserve not to be) generally adopted.

We have seen that an insect in the final state has six true legs. Yet even here many species depart from the rule, as there are many in which the perfect insect, especially in the female s.e.x, is apodous or without legs, just as there are also other cases where they are without wings.

Sometimes the legs seem to be reduced in number by the partial or total atrophy of one or the other pair, but in all these exceptional cases there is no difficulty in realizing that we have to deal with a true insect, because of the other characters pertaining to the cla.s.s, some of which it will be well to allude to.

Insects are further characterized by having usually three distinct divisions of the body, viz.: head, thorax, and abdomen, and by undergoing certain metamorphoses or transformations. Now, while a number of other animals outside of the insect world go through similar transformations, those in the Crustacea being equally remarkable, yet, from the ease with which they are observed and the completeness of the transformations in most insects, the metamorphoses of this cla.s.s have, from time immemorial, excited the greatest curiosity.

SCOPE AND IMPORTANCE OF ENTOMOLOGY.

But few words are necessary to indicate the importance of entomology, especially to the farming community; for while insects play a most important part in the economy of nature and furnish us some valuable products and otherwise do us a great deal of indirect good, yet they are chiefly known by the annoyances they cause and by the great injury they do to our crops and domestic animals. Hence some knowledge of insects and how to study them becomes important, almost necessary, to every farmer.

The scope of the science may best be indicated by a statement of the number of species existing, as compared with other animals. The omnipresence of insects is known and felt by all; yet few have any accurate idea of the actual numbers existing, so that some figures will not prove uninteresting in this connection. Taking the lists of described species, and the estimates of specialists in the different orders, it is safe to say that about thirty thousand species have already been described from North America, while the number of species already described or to be described in the Biologia Centrali-Americana, i. e., for Central America, foot up just about the same number, Lord Walsingham having estimated them at 30,114 in his address as president of the London Entomological Society two years ago, neither the Orthoptera nor the Neuroptera being included in this estimate. By way of contrast the number of mammals, birds, and reptiles to be described from the same region, is interesting. It foots up 1,937, as follows:

Mammals, 180; birds, 1,600; reptiles, 157.

If we endeavor to get some estimate of the number of insects that occur in the whole world, the most satisfactory estimates will be found in the address just alluded to, and in that of Dr. David Sharp before the same society. Linnaeus knew nearly 3,000 species, of which more than 2,000 were European and over 800 exotic. The estimate of Dr. John Day, in 1853, of the number of species on the globe, was 250,000. Dr. Sharp's estimate thirty years later was between 500,000 and 1,000,000. Sharp's and Walsingham's estimates in 1889 reached nearly 2,000,000, and the average number of insects annually described since the publication of the Zoological Record, deducting 8 per cent for synonyms, is 6,500 species. I think the estimate of 2,000,000 species in the world is extremely low, and if we take into consideration the fact that species have been best worked up in the more temperate portions of the globe, and that in the more tropical portions a vast number of species still remain to be characterized and named, and if we take further into consideration the fact that many portions of the globe are yet unexplored, entomologically, that even in the best worked up regions by far the larger portion of the Micro-Hymenoptera and Micro-Diptera remain absolutely undescribed in our collections, and have been but very partially collected, it will be safe to estimate that not one-fifth of the species extant have yet been characterized or enumerated. In this view of the case the species in our collections, whether described or undescribed, do not represent perhaps more than one-fifth of the whole.

In other words, to say that there are 10,000,000 species of insects in the world, would be, in my judgment, a moderate estimate.

CLa.s.sIFICATION OF HEXAPODS.

Seven orders of insects were originally recognized by Linnaeus, namely, Neuroptera, Diptera, Hemiptera, Lepidoptera, Coleoptera, Hymenoptera, and Aptera. This cla.s.sification was based on the organs of flight only, and while in the main resulting in natural divisions which still furnish the basis of more modern cla.s.sifications, was faulty in several particulars. For instance, the Aptera, which included all wingless insects, was soon found to be a very unnatural a.s.semblage and its components were distributed among the other orders. The establishment of the order Orthoptera by Olivier to include a large and well-defined group of insects a.s.sociated with the Hemiptera by Linnaeus, restored the original seven orders, and this cla.s.sification has, in the main, been followed by entomologists up to the present time.

[Ill.u.s.tration: FIG. 1.--Pyramid showing the nature of the mouth, and relative rank of the Orders, and the affinities of the Suborders of Insects.]

All insects are, in a broad way, referable to one or the other of these seven primary orders by the structure of the wings and the character of the mouth-parts in the imago, and by the nature of their transformations.

Some of these orders are connected by aberrant and osculant families or groups, which have by other authors been variously ranked as independent orders, but which, following Westwood substantially, I have considered, for convenience, as suborders. (_See_ Fifth Report, Insects of Missouri, etc., 1872.)

In the article just cited, I made use of the accompanying diagram in the form of a pyramid (Fig. 1), which gives a graphic representation of the distinguis.h.i.+ng characters and the relative rank as usually accepted, of the orders and suborders.

Full discussion of the different cla.s.sifications is unnecessary in this connection. Authors have differed in the past and will differ in the future as to what const.i.tutes a natural system, and it would require many pages to give even a brief survey of the various schemes that have been proposed. As I have elsewhere said, "We must remember that cla.s.sifications are but a means to an end--appliances to facilitate our thought and study--and that, to use Spencer's words, 'we cannot, by any logical dichotomies, actually express relations which in nature graduate into each other insensibly.'"

The most philosophical, perhaps, of the more modern systems of cla.s.sification is that of Friedrich Brauer, who has carefully studied the subject, and has given us an arrangement consisting of sixteen orders. This has many merits and has been adopted, with slight modifications, by Packard in his "Entomology for Beginners," and by Hyatt and Arms in their recent and valuable text-book "Insecta."

Comstock, in his "Introduction to Entomology" strongly recommends Brauer's cla.s.sification, but for reasons of simplicity and convenience adheres to a modification of the old cla.s.sification of Westwood.

For purposes of comparison the cla.s.sification by Hyatt and Arms, which is substantially that of Brauer, may be introduced.

In linear arrangement it is as follows:

I. Thysanura (_Spring-tails_, etc.).

II. Ephemeroptera (_Ephemeridae_; May-flies). (=_Plectoptera_ Pack.) III. Odonata (_Libellulidae_; Dragon-flies).

IV. Plecoptera (_Perlidae_; Stone-flies).

V. Platyptera (_Termites_, _Mallophaga_, etc.).

VI. Dermaptera (_Forficulidae_; Earwigs).

VII. Orthoptera (Locusts, Gra.s.shoppers, etc.).

VIII. Thysanoptera (_Thripidae_; Fringe-wings).