December 14, 1893] 



NATURE 



147 



and examples which are contained in the text and at the 

 end of the chapters. Persons whose curiosity is limited 

 to finding out 7u/iai electricity docs, and adopt the un- 

 scientific attitude of considering it waste of time to try 

 and ascertain luhat electricity is, and why it is capable 

 of performing so many wondrous feats, may perhaps 

 rebel against a system, one of whose objects is to train 

 the mind to inquire into the causes of natural phenomena. 

 It must be recollected that young men, who are just 

 emerging from the schoolboy stage of existence, invari- 

 ably find that Rigid Dynamics is a very difficult subject to 

 master, and that a thorough knowledge of the principles 

 of the subject, combined with analytical skill in applying 

 ihem to natural phenomena, can only be acquired by 

 working out a large number of problems and examples. 

 It is also an excellent plan for students to work out the 

 same problem (for example, the motion of a top) by 

 various methods, and to study the different results ob- 

 tained by each ; for they will thereby not only obtain 

 analytical skill, but will learn that their symbols, instead 

 of representing mere mathematical quantities, are the 

 embodiment of important scientific facts. 



A. B. Basset. 



INSECT PESTS. 

 Our Household Insects : an Account of the Insect Pests 

 found in Dwelling-houses. By Edward A. Butler, 

 B.A., B.Sc.Lond., author of "Pond Life," "Silk- 

 worms," &c. (London and New York: Longmans, 

 Green and Co., 1893.) 



MR. E. A. BUTLER has done useful service to the 

 cause of popular ento.iiology by reprinting the 

 present series of his contributions to Knowledge in book 

 form. Not very many species are discussed, but these 

 seem to comprise most of the principal insect pests be- 

 longing to the various orders of insects which infest our 

 houses, and attack ourselves or our property. 



As insects (e.xclusive of insect-parasites) attack all 

 kinds of dead or decaying animal and vegetable matters, 

 and play the part of general scavengers, nothing is 

 exempt from their ravages. Books are particularly sub- 

 ject to their attacks ; and many of their enemies are 

 noticed by Mr. Butler. We remember once being much 

 amused by an account of a book-worm, which was ridi- 

 culed by a writer in a bibliographical magazine, as being 

 evolved from the describer's own consciousness, but which 

 was really fairly recognisable as applicable to Lepisnia sac- 

 charina,\.h.& common silver-fish. But the critic regarded 

 the book-worm as necessarily a small grub or beetle (we 

 forget which), and displayed his own ignorance of ento- 

 mology accordingly. Prof. Westwood once named a 

 minute beetle, which had done much mischief to the ' 

 cover of a book, Hypotheneinus eruditus; and specimens 

 of books damaged by insects may be seen in one of the | 

 cases in the public insect-room at the Natural History 

 -Museum, South Kensington. We believe that Mr. 

 Zaehnsdorf, the well-known book-binder, has also formed 

 a collection of the book-pests which he has met with in 

 the exercise of his vocation. We may add that the Arabs 

 sometimes write the name Kabikaj, said to be that of a 

 genius who presides over insects, on their manuscripts, 

 m order to protect them from the ravages of his subjects. 

 NO. 1259, VOL. 49] 



I There is no doubt that insects of various kinds get 

 [ mixed with human food from time to time ; but we 

 imagine that the passage which Mr. Butlef quotes from 

 Curtis's "Farm Insects," relating to maggots in cocoa- 

 beans, is somewhat out of place at the end of a chapter 

 on beetles, for we have good reason to believe that the 

 insect to which Curtis alluded was not a beetle, but a 

 moth of the genus Ephestia. 



The seven plates of magnified insects and their struc- 

 ture, and the numerous woodcuts, add much to the use- 

 fulness of the book. Clear definitions, and accurate 

 demonstration?, are extremely useful in entomology, not 

 merely to beginners, but even to more advanced student?, 

 who often find much difficulty in obtaining the necessary 

 explanations of the characters and terminology, when 

 they take up the study of a group of insects with which 

 they were not previously familiar. 



The insects which Mr. Butler discusses may be divided 

 into three classes : those which really cause serious de- 

 struction to property, as the clothes-moths and various 

 kinds of small beetles ; those which are rather trouble- 

 some and annoying than destructive, such as the flies 

 and wasps ; and those which attack man himself. 

 Among the latter are the lice, which the increase of 

 cleanliness has fortunately rendered rather unfamiliar 

 objects to the better classes in recent times. Yet they 

 are highly interesting creatures, from many points of 

 view, and several entomologists have not scrupled to 

 make a special study of them ; among others, Denny, 

 who wrote an elaborate monograph on the British species, 

 illustrated with twenty-six coloured plates ; and the old 

 Dutch naturalist. Van Leeuwenhoek, who actually reared 

 a brood in a stocking on his own leg ! We think the 

 figure of the proboscis of a louse, which Mr. Butler copies 

 from the Danish entomologist Schiodte, on p. 332, will 

 be new to most of his readers. But there is a curious 

 omission of a necessary explanation in Mr. Butler's 

 observations, in the following passage : — 



" Man is not exceptional among mammals in harbour- 

 ing these vermin ; he is but in the same category with 

 the rest, for it seems to be the rule, from elephant to 

 mouse, largest to least, that some member of this group 

 of parasites should be attached to each species ; and 

 even aquatic animals, such as the seal and walrus, do not 

 evade their attacks." 



Surely Mr. Butler, to avoid being misunderstood, 

 should here have stated that the presence of a true louse 

 on seals is quite an exception as regards marine animals, 

 and that the so-called " whale-louse," and similar para- 

 sites, are not true lice, or even insects at all, but 

 parasitic Crustacea. 



Our author mentions the fact of colonies of fleas 

 having sometimes been found on sandy sea-shores, and 

 wonders what they can find to eat there. But although 

 certain species of fleas are attached to different species of 

 animals, they are perhaps not so particular about their 

 food as is generally supposed. In all warm countries it 

 is very common to find colonies of fleas camping-out in 

 the open ; and the late Mr. F. Smith once recorded an in- 

 stance of a suburban garden, in which a particular bed was 

 swarming with dog-fleas ; no particular dog being men- 

 tioned as the probable origin of the invasion. In the 

 Western States of America, the " wild fleas," as the late 



