May 1, 1897.] 



KNOWLEDGE. 



105 



LONDON: MAY 1, 1897. 



CONTENTS. 



The Insects of a London Back-Garden. — I. Bv Feed. 



Exocic, F.L.S., F.E.S. (lUustrated) 



Science Notes 



Biological Progress in the Victorian Era. By E. 



Lydekkee, U.A.Cantab., F.E.S. (Plate) ' ... 



Sixty Years of Geological Research. Bt Gbesville 



A. J. Cole, M.E.I.A., F.Cf.S. (niustrated)' ... ... 



Notices of Books 



Shoet Notices 



Books Eeceived 



Letters: — W. H. S.Moxck; A. Fotvlee 



On the Vegetation and Some of the Vegetable 



Productions of Australasia.- II. By W. Botting 



Hemsley. F.K S , F.L.S. (lUustrated) 



The Nebula round i) Argus. By E. Waltee MArxcEE, 



F.E.A.S. (Plate) 



The Superstitions of Shakespeares Greenwood. By 



Geoege Mokley 

 Why do you Photograph ? BtT. A. Geeald Steicklakd, 



F.F.!<. (Illustrafed)... 



The Face of the Sky for May. By H. Sadlee, F.R.A.S. 

 Chess Column. By C. D. LococK, B.A.Oion 



1(15 

 1C9 



110 



112 

 115 

 117 

 117 



117 



118 



120 



122 



124. 

 127 

 127 



THE INSECTS OF A LONDON BACK-GARDEN.-I. 



By Fred. Enock, P.L.S., F.E.S. 



IF there ia one thing above another which impressea 

 itself upon the mind of a stranger coming up from 

 the country, surely it is the view of the London 

 "backs," as seen from the carriage windows, when 

 the train threads its way through the crowded 

 suburbs. From some of these London " backs '' I have 

 derived much pleasure in studying the creeping nnd flying 

 things found in such places — things which country people 

 scarcely ever see (because they never look for them), and 

 thus our knowledge of insects is chiefly derived from the 

 work of town naturalists. 



London back gardens vary considerably in length, but 

 thirty feet is about the average. In such a "back" I have 

 found creeping things innumerable — some altogether new 

 to science. This may be owing to the encouragement 

 given to insects to come and congregate where they will be 

 looked after ! The first appearance of a new garden is not 

 prepossessing — a square of grass, termed a/ii"*;, surrounded 

 by a narrow pathway covered with coarse burnt-ballast, 

 and a narrow strip of ground into which it is not advisable 

 to dig to a greater depth than six inches, unless we are 

 desirous of starting a museum of present-day kitchen 

 utensils, together with various types of foot-gear. The first 



and best thing to do is to endeavour to raise a background at 

 the end of the garden. This is easily managed by utilizing 

 the wisps of willow with which bundles of rhubarb are bound 

 up in April. A dozen of such cuttings put in and well 

 watered will soon strike and grow up quickly, and become 

 peopled with all sorts of insects during the first year. The 

 well-known green fly or "blight" is only too plentiful, 

 and every flower and shrub has its peculiar kind, whose 

 identity can easily be ascertained from Buckton's " British 

 Aphidre ' ' (Ray Society) . The prodigious rate at which these 

 mild-looking insects increase is almost past our conception, 

 and certainly few people believe it possible. Nevertheless 

 it is a fact that but for the army of parasites whose larv;e 

 feed inside the green flies, while those of other flies feed 

 direct upon the bUght, so keeping a constant check upon 

 their imdue increase, they would so multiply that every 

 green leaf would soon be consumed. 



Our knowledge of these benefactors is very small indeed, 

 and yet nothing can be easier than the breeding of now 

 species. All that is necessary is to carefully collect the 

 largest aphids, placing them in a phial with a label having 

 the date and name of flower or tree from which the flies 

 have been taken. In a few days or weeks the parasites 

 will emerge, when they should be killed, set on card, and 

 carefully numbered — a corresponding number being kept in 

 a diary, with all particulars concerning the date of emer- 

 gence and the plant from which the aphis had been taken. 

 Such a work, systematically carried out, would be of great 

 scientific value. 



It ia most interesting, on a bright, sunny morning, 

 to watch one of these busy little parasites, such as 

 AphiiUus, at work among a swarm of Aplddce. Settling 

 upon a leaf, it at once proceeds to sound the first 

 " fly " with which it comes into contact by tapping it upon 

 its back with its long antenn:^ —those sensitive organs 

 through which is conveyed to the brain the knowledge that 

 the green fly is or is not a suitable one wherein to lay an egg. 

 If the aphis does not already possess an egg in its stomach, 

 the parasite leaps upon its back, holding on with a firm 

 grasp with its tiny bifid claws. The point of the ovipositor 

 is quickly brought down upon the back and a hole drilled 

 through, in spite of the resistance of the aphis, which is 

 compelled to take in a lodger. This egg soon hatches to 



the 



a maggot, which feeds upon tne jiuce contained m 

 stomach, so stimulating the appetite of its host, which 

 increases in size until it is ready for its next change to the 

 pupa. But while it has been growing, the internal 

 parasite has been doing the same, and has almost reached 

 its full growth. The aphis has not strength to go through 

 its change, so, spreading out its legs, it takes a firm 

 hold on to the leaf and dies, and the parasite completes 

 its growth by feeding upon the remaming juice. The 

 host's body then becomes hard and dry, retaining its 

 distended form. In the course of a week or more the 

 parasitic larva changes to a pupa in the stomach of its 

 dead host, or hostess (generally the latter) ; and on arriving 

 at maturity, which it does upon its back, with the head 

 towards the tail of the aphis, it commences to bite an 

 aperture through the dried skin. Moving its head round 

 on its neck, it cuts out with its sharp teeth a small circu- 

 lar piece. Its head is soon thrust through, followed by the 

 first pair of legs ; then the antenn;u are freed one by one — next 

 the second legs are carefully withdrawn, and a firm hold 

 obtained on the skin of the late hostess. The wings are 

 gradually worked out a short way, followed by the with- 

 drawal of the third and last pair of legs ; the wings are 

 then easily completely withdrawn, quickly followed by the 

 abdomen, which at first is much distended, but after the 

 discharge of fluid it soon assumes its natural shape ; the 



