^ LIBRARY CIRCULAR NO. 4.9. SECOND SERIES. STATE PLANT BOARD j United States Department of Agriculture, y DIVISION OF ENTOMOLOGY, \ A ^ L. O. HOWARD. Entomoloeist. THE SILVER FISH. {Lepisma saccharina Linn.) By C. L. Marlatt, First Assistant Entomologist. [Revised reprint from Bulletin No. 4, New Series. Division of Entomology, U. S. Department of Agriculture, pp. 76-78.] This insect (fig. 1) is often one of the most troublesome enemies of books, papers, card labels in museums, and starched clothing, and occasionally of stored food substances. Its peculiar fish-like form and scaly, glistening body, together with its very rapid movements and active efforts at concealment whenever it is uncovered, have attached considerable popular in- terest to it and have resulted in its re- ceiving a number of more or less descrip- tive popular names, such as silver fish, silver louse, silver witch, sugar fish, etc. The species named above is the common one in England, but also occurs in this country, and like most other 'domestic insects, is now practically cosmopolitan. It has a number of near allies, which closely resemble it, both in appearance and habits. One of these (Lepisma [ThermoMa] domestica Pack.) has cer- tain peculiarities of habit which will be referred to later. The peculiar appear- ance of the common silver fish early drew attention to it, and a fairly accu- rate description of it, given in a little work published in London in 1665 by the Royal Society, is interesting enough to reproduce : It is a very small, silvery, shining worm or moth which I found much con- versant among books and papers, and is supposed to be that which corrodes and eats holes through the leaves and covers. It appears to the naked eye a small, glittering, pearl-colored moth, which upon the removing of books and papers in the summer, is often observed very nimbly to scud and pack away to some lurking cranny where it may better protect itself from any appearing dangers, life head appears big and blunt, and its body tapers from it toward the tail, smaller and smaller, being shaped almost hke a carret.i Fig. 1.— Lepisma saccharina , enlarged (original). adult- Micrographia, R. Hooke, London, 1665. 2 On account of its always shunning the light and its ability to run very rapidly to places of concealment, it is not often seen and is most difficult to capture, and being clothed with smooth, glistening scales, it will slip from between the fingers and is almost impossible to secure without crushing or damaging. It is one of the most serious pests in libraries, particularly to the binding of books, and will frequently eat oS the gold lettering to get at the paste beneath, or, as reported by Mr. P. R. Uhler, of Baltimore, often gnaws off white slips glued on the backs of books. Heavily glazed paper seems very attractive to this insect, and it has frequently hap- pened that the labels in museum collections have been disfigured or destroyed by it, the glazed surface having been entirely eaten off. In some cases books printed on hea- vily sized paper will have the surface of the leaves a good deal scraped, leaving only the portions covered by the ink. It will also eat any starched clothing, linen, or cur- tains, and has been known to do very se- rious damage to silks which had probably been stiffened w i t h sizing. Its damage in houses, in addition to its injury to books, consists in causing the wall paper to scale off by its feeding on the starch paste. It occasionally gets into vegetable drugs or similar material left undisturbed for long periods. It is reported also to eat occasionally into carpets and plush-covered furniture, but this is open to question. The silver fish belongs to the lowest order of insects — the Thysa- nura — is wingless, and of ver}^ simple structure. It is a worm-like insect about one-third of an inch in length, tapering from near the head to the extremity of the body. The head carries two prominent antennae, and at the tip of the body are three long, bristle-shaped appendages, AG CA T Fid. 2.— Lepismadomestica: Adult female— enlarged (original). one pointing directly backward and the other two extending out at a considerable angle. The entire surface of the body is covered with very minute scales like those of a moth. Six legs spring from the thorax, and, while not very long, they are powerful and enable the insect to run with great rapidity. In certain peculiarities of structure, and also in their habits, these anomalous insects much remind one of roaches, and their quick, gliding movements and flattened bodies greatly heighten this resemblance. More striking than all, however, is the remarkable development of the coxae or basal joints of the legs in the silver fish, which finds its coun- terpart in roaches, and, taken in connection with the other features of resemblance, seems to point to a very close alliance between the two groups, if, indeed, the silver fish are not merely structurally degraded forms of roaches and to be properly classed with the Blattida. Another of the common silver fishes of this country, referred to in the opening paragraph, has developed a novel habit of frequenting ovens and fireplaces, and seemingly revels in an amount of heat which would be fatal to most other insects. It disports itself in numbers about the openings of ranges and over the hot bricks and metal, manifesting a most surprising immunity from the effects of high temperature. This heat-loving or bakehouse species (fig. 33) was described in 1873 as Lepisma domestica by Packard, who reported it to be common about fireplaces at Salem, Mass. This species is also very abundant in Wash- ington. What is evidently this same insect has become very common, particularly in the last year or two, in England and on the Continent, where it manifests the same liking for hot places exhibited by it in this country. The habit of this species of congregating in bakehouses and dwellings, about fireplaces and ovens, has given rise to the common appellation for it in England of " fire-brat." Similar descriptive names are applied to it also on the Continent. This species closely resembles the common silver fish in size and general appearance, but may be readily distinguished from it by the presence on the upper surface of dusky markings. It also possesses well-marked structural differences, which have led to its late reference to a distinct genus — Thermobia. An Italian entomologist, Rovelli, has described this insect under the descriptive name furnorum, from its inhabiting ovens, and the name of the genus to which it is now assigned by English entomologists is also descriptive of its heat-loving character. A Dutch entomologist, Oude- mans, reports that he has found it in abundance in all bakehouses that he has examined in Amsterdam, where it is well known to bakers and has received a number of familiar names. REMEDIES. Advantage may be taken of the liking of these insects for fabrics and other articles containing starch to poison them by slipping into all the A6 64 UNIVERSITY OF FLORIDA 3 1262 09228 3588 crevices where they occur — in bookshelves and backs of mantels, under washboards, and in the bottoms of drawers — bits of cardboard on which a thick boiled starch paste liberally poisoned with arsenic has been spread and dried. One of our correspondents reports complete relief by this measure. The silver fish readily succumbs to pyrethrum, and wherever this can be applied, as on bookshelves, it furnishes one of the best means of control. For starched clothing and similar objects liable to be injured by it, frequent handling and airing and the destruction by hand of all specimens discovered is to be recommended, in addition to the poisoned cardboard remedy. Little damage is liable to occur in houses except in comparatively moist situations or where stored objects remain undisturbed for a year or more. Washington, D. C, June 20, 1902. O A6 64