Unfortunately for the well-being of collections, dried insects are liable to the attacks of various museum pests, the most troublesome of which are themselves insects, but altogether out of their proper place and rÔle in the general collection. Unless constant precautions are taken, the collector will discover after a few months that instead of the rare specimens with the preparations of which he has taken no little pains there remains only a series of fragmentary specimens, which a few years' neglect will reduce to little more than a mass of dust or powder. The price, then, of a good collection is eternal vigilance. Most insects, when exposed for any length of time to strong light, fade or lose color, and the only way to prevent such achromatism is to exclude the light.

Insect pests affecting collections include PsocidÆ, Mites, TineidÆ, Coleoptera of the families PtinidÆ and DermestidÆ, these last being the most injurious.

The PsocidÆ—degraded wingless insects already referred to in the classification (p. 24)—will find their way into the tightest boxes, but ordinarily do little if any damage, except in the case of delicate insects, such as Ephemerids, Microlepidoptera, and Microdiptera. The common forms found in collections are Atropos divinatorius and Clothilla pulsatoria. Mites or Acari are rarely troublesome in collections, though Dr.H.A.Hagen reports having found a species (probably of Tyroglyphus) with imported insects, and considers them as liable to become dangerous enemies. Tineid larvÆ are rarely found in collections, and only affect the larger moths. They are not easily discovered, since they make no dust, as do most other pests. Some persons have been considerably annoyed by one of the common clothes moths, Tineola biselliella (Fig.121). Dr.Hagen found that it attacked freshly collected or newly spread insects, where the spreading-boards were left uncovered, but Mr.F.M.Webster has found it injurious to the general collections at Columbus, Ohio.

Of beetles, the PtinidÆ are sometimes found in collections but are not common. Two species are known to attack entomological specimens, namely, Ptinus fur, which is quite rare, in this country, but much more abundant in Europe, and Tribolium ferrugineum, a cosmopolitan species which, however, has several times been associated in injurious numbers with large collections of insects imported from the East Indies.

But by far the most dangerous enemies of insect collections are the larvÆ of some half dozen or more species of DermestidÆ belonging to the genera Anthrenus, Attagenus, Trogoderma, and Dermestes. Of these Anthrenus varius is the more common pest, in museums, especially in the North and East. In the South and West Trogoderma tarsale and T. ornatum (?) replace Anthrenus. The European species Anthrenus musÆorum, is, on the authority of Hagen, rare in this country, and probably occurs chiefly in collections of imported insects. It is the common injurious species of Europe. Anthrenus scrophulariÆ (see Fig.67) occurs also in collections, Dr.Hagen stating that he has found it nearly as common as A. varius, and certainly more dangerous. In my own experience it is rarely found in insect collections. Two species of Attagenus (A. pellio and A. megatoma) have also been found in collections. A. megatoma has been found by Dr.Hagen to do not a little damage to insect collections in Cambridge, as well as to equal if not exceed the Carpet Beetle in its disastrous attacks upon carpets and household furniture. The other species, A. pellio, is rarely found in this country, but is much more common and obnoxious in Europe than A. megatoma. Dermestes lardarius is sometimes found in collections, and is attracted by the presence of animal matter such as skins, etc. The two particularly destructive pests, as pointed out, are Anthrenus varius and Trogoderma tarsale. These species, together with most of the others, have no definite breeding period, but, in the uniform temperature of the laboratory or museum, breed all the year round and present no definite broods. It is the experience at the Museum that the boxes on the lower tier of shelves are very much more subject to attack than those on the upper tiers, from which it would seem that the parent beetle deposits her eggs outside the boxes on the floor of the cases and that the young larvÆ work their way into the smallest crevices. The danger of infection by these pests is greater in warm climates like that of Washington than in regions further north, as the warm season begins earlier, lasts longer, and furnishes better conditions for breeding and multiplication.Remedies.—The following remedies and preventives will prove efficient in checking or preventing the work of these pests.

Naphthaline.—Where tight boxes are employed little fear of the work of these destructive agents need arise, especially if the boxes are kept supplied with repellent naphthaline cones. These are hard cones of naphthaline, mounted on pins for convenient placing in the boxes (see Fig.122), and may be obtained of dealers in entomological supplies. Naphthaline cones act as repellents to these insects and also to some extent retard the development of the larvÆ in all stages and particularly of the eggs.

Mr.Schwarz states (Proc. Ent. Soc. of Washington, Vol. i, page 63) that in place of these cones a form of naphthaline may be used which is known in commerce as “white carbon,” and is put up in the form of small square rods for use in intensifying the flames of gaslight. The material is very cheap, costing only 8 cents per pound wholesale, and may be broken up into small pieces, wrapped in paper, and pinned. The use of naphthaline cones is not advisable in boxes containing delicate specimens, as it leaves a deposit which dulls the colors and encourages greasing. The deliquescence of the naphthaline cones produces a blackish, oily residuum which will soil the lining of the box, and it is always advisable either to pin a piece of blotting paper beneath the cone or to wrap this in paper.

Constant watchfulness is necessary to see that the eggs which have been deposited and checked in development by the application of this insecticide do not ultimately hatch and start a new generation in the insect box.

Bisulphide of Carbon.—If the collection is found to be infested with insect pests, it may be renovated by pouring a little bisulphide of carbon into the boxes and closing them at once. This substance evaporates rapidly and will destroy all insect life, and does not injure specimens or pins nor stain the boxes. If infested specimens are received, these should be inclosed in a tight box and treated with bisulphide of carbon before being added to the general collection, and it is always well for those who are receiving pinned specimens by exchange or otherwise to keep a quarantine box of this kind on hand.

Mercury Pellets.—The use of mercury pellets is recommended to free boxes from Mites, Psoci, etc., and also to collect any particles of dust which may gain entrance. A few small pellets of mercury, placed free in the bottom of the horizontal box will, by the movement of the box, be caused to roll to and fro and accomplish the desired end.

Carbolic Acid.—Mr.A.T.Marshall (Entomologist's Monthly Magazine, Dec., 1873, p. 176) records that he washes the paper of his boxes with the common disinfecting solution of carbolic acid in two-thirds water, which dries without staining and protects the specimens from Psoci.

A Means of preserving Insects in dry hot Countries.—In the “HorÆ Societatis EntomologicÆ RossicÆ,” XXIV, pp. 233, 234 (1889), M. A. Wilkins, writing from Tachkent in Turkestan, alludes to the inefficiency of ordinary preservatives in Central Asia, on account of their rapid volatilization through the hot dry air, so that if a collection be neglected for only two or three months Anthreni are sure to be found in the boxes. He has hit upon a plan which he finds effective, and at the same time very simple. He employs India-rubber bands about 1½ inches in width and less than the length of the boxes to which they are to be applied. These bands are stretched over the opening line of the boxes, and effectually prevent the entrance of the most minute destroyers. Possibly a similar plan might be adopted in other countries with a like climate. At any rate, the method has the merit of extreme simplicity. (The Ent. Mo. Mag., Apr., 1891, p. 107.)

MOLD.

Collections kept in damp places or in a moist climate are very liable to mold, and under such conditions it is difficult to avoid this evil. Carbolic acid is recommended, but Mr.Ashmead, who has kept a large collection in the moist climate of Florida, has found the use of naphthaline much more satisfactory. Mr.Herbert H.Smith who has had more extensive experience in the tropics prefers the carbolic acid. Moldy specimens may be cleansed by washing with carbolic acid applied with a fine camel's hair brush.

VERDIGRISING AND GREASING.

The action of the acid juices in the bodies of certain specimens—as many of the Lepidoptera, Coleoptera, and Diptera—will cause the formation of verdigris about the pin, which in time accumulates and disfigures and distorts the specimen, and ultimately corrodes the pin, so that the slightest touch causes it to bend or break. There is no preventive yet known for this trouble other than the use of pins which have no brass to be corroded. Japanned pins are made for this purpose, and are, on the whole, satisfactory, but they bend easily and some caution is required in handling them. In place of these pins, which are somewhat more expensive than the steel pins, iron pins may be used. These are very soft and bend too easily for satisfactory use. The steel pins may be rendered available for use by an immersion in a silver bath, which is comparatively inexpensive.

Insects the larvÆ of which live in wood are particularly subject to verdigris, as the CerambycidÆ and ElateridÆ in Coleoptera, the UroceridÆ in Hymenoptera and SesiidÆ in Lepidoptera. In Hymenoptera the families FormicidÆ, MutillidÆ, and the endophytous TenthredinidÆ verdigris very rapidly, and most Diptera also. With all these insects japanned or silvered pins should be used, or when not too large the insects should be mounted on triangles. This verdigrising is associated with what is known as greasing, and this, as just indicated, is also associated with endophytous larval life. The verdigris may be prevented by the methods indicated, and I would strongly advise, as a good general rule to be followed, the rejection of the ordinary pins for all species which, in the larva state, are internal feeders. But there is no way of preventing greasing or decomposition of the fats of the body, which may affect a specimen years after it has been in the cabinet. If the specimen is valuable the grease may be absorbed by immersion in ether or benzine, or by a longer treatment with powdered pipe-clay or plaster of Paris. Insects collected on seabeaches, and saturated with salt water, also corrode the common steel pin very quickly and should be mounted on japanned pins. It is also advisable to rinse such specimens thoroughly in fresh water before mounting.

The conviction has been forcing itself on my mind for some time that the naphthaline cones tend to promote greasing and verdigris, and carbolic acid in some small vessel secured to the cork, were, perhaps, preferable.