July 1, 1891.] 



KNOWLEDGE 



121 



AN ILLUSTRATED 



MAGAZINE OF SCIENCE 



SIMPLY WORDED— EXACTLY DESCRIBED 



LONDON: JULY 1, 1891. 



CONTENTS. 



PAGE 



Gnats. Midges, and Mosquitos. By E. A. Butler 121 

 On the Plan of the Sidereal System. By J. R. StTTOx, 



B.A.Canhih 123 



The Experimental Method in Geology. l?y Vmgban 



C.iTiNi^ii, B.Sf.. F.C.S. 12.5 



Flying Animals. By R. I.tpkkkkh, B.A Cantiib. 127 

 The Companion to ,i Ursa; Majoris ip 1077i. B\ S. \V. 



Btknhaii 12ii 



Astronomy as taught by Academy Pictures I2li 

 Birds and Berries. Bv tin- Ri'v. Ai.k.\. .s. \Vu..--mn. M.A.. 



B.Sc ' VM) 



Notices of Books . 132 



Letters: — W. H. S. Moxck ; E. W. Mauxdeb ; C. LtMi; H. 



Christopher; H. y, HrTCHixsox; R. C'hahtres 133 



The Potato Fungus. By .1. Pentland Smith. M.A.. 



B.Sf., &<•. 13.-) 



The Face of the Sky for July. By Herbert Sadler, 



F.R.A.S 137 



Whist Column. By W. JIontago Gattie. B.A.Oxoii. 1.3,S 



Chess Column. By C. D. Locock, B.A.Oxon 139 



NOTICE. 



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 Cheques and Postal Orders should be made payable to 

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GNATS, MIDGES AND MOSQUITOS.-I. 



I'.Y !',. A. lirTI.RK. 



UNDER these names are included a variety of small, 

 delicately constructed flies, the very types, in the 

 insect world, of slenderness, grace, and fragility, 

 lint fairy-like elegance of form is no guarantee of 

 gentleness of disposition, and it is united, in the 

 case of •«*»'(' of these insects, with n persistence and hardi- 

 hood in attack, and a bloodthirstiness of nature, that 

 make them some of the most intolerable of pests. In this 

 country, it is true, we are now, for reasons which will 

 appear later on, tolerably free from annoyance on their 

 part ; but as they are world-wide in distribution, ranging 



from the tropics to the Arctic zone, there are many less- 

 favoured lands, in which they still exist in countless 

 myriads, and in which their extermination would be 

 bailed, whether justifiably or not, as an unmixed blessing. 

 They form a sub-section of the enormously extensive order 

 of Diptera, or two-winged tlies, an order which is probably 

 responsible for the infliction of a larger amount of suffering 

 and annoyance upon human beings and other vertebrate 

 animals than can be charged upon any other. At least 

 two very distinct types of Diptera may be recognised ; on 

 the one hand, there are stout-bodied and comparatively 

 short-legged flies, with minute and curiously shaped 

 antennae like those of the blow-fly, and on the other, 

 slender-bodied exceedingly long-legged flies, with antenna; 

 of ordinary size and of less extraordinary shape. To the 

 former division (/>'/v;(7i//cf;r( = short-horns) are referred the 

 house-flies and allied insects discussed on a former occasion 

 in our papers on " House-flies and Bluebottles," as well as 

 hosts of others less familiar ; while to the latter {Xt'tnocera 

 = thread-horns) belong a weak-limbed and fragile gi'oup, 

 the daddy-long-legs or crane-flies, together with the 

 numerous kinds of gnats, mosquitos, midges, merry- 

 dancers, &c. (though not the equally, or even still more, 

 fragile May-flies or day-flies). It is with the section 

 Nemocera, therefore, viz. the "thread-horned" flies, that 

 we are now concerned. 



There is amongst the members of this group a striking 

 variety, both as to habits and life-history. Some, in their 

 early stages, lead an active life in the water ; others, of a 

 more sluggish temperament, inhabit fungi or rotten wood ; 

 others, again, like the notorious Hessian fly, are parasitic 

 on plants, producing gall-like excrescences within which 

 they reside ; while yet others, hke the daddy-long-legs, 

 whose larvfe are the detested '-leather-jackets" of the 

 gardener, live underground, devouring roots of plants as 

 well as vegetable refuse. It might be expected that, with 

 such diversity of habits, there would be correspondingly 

 great differences of form in the adult insects. Such, bow- 

 ever, can scarcely be said to be the case, and thus many 

 that are superficially similar in the adult condition may 

 have passed through their preliminary stages under totally 

 different circumstances. This fact, coupled with the 

 fragile and easily damaged structure, and consequent 

 difficulty of preservation, the obscure colours, and the com- 

 paratively unmarked characters of the perfect insects, 

 makes the nice discrimination of species a very diihcult 

 task, and it is not surprising that the popular judgment 

 has declined this task, and has seen in all these different 

 creatures but varieties for which three or four names at 

 the outside will suffice. Our first business, therefore, must 

 be, as is usually the case in dealing with insects under 

 their popular names, to define our terms, and to say what 

 insects we include and what we exclude, and in what sense 

 we use the terms " gnats, midges, and mosquitos." 



Without in the least attempting accurately to distinguish 

 species, it may suffice to say that, when we speak of gnats 

 and mosquitos as household pests, we do not by any means 

 refer to all gnat-Uke creatures, nor even to all which would 

 commonly bo called gnats, but only to such as belong to 

 one particular family, the Ciiliridtr, and which, by their 

 blood-sucking propensities, trouble mankind indoors, either 

 in this country or elsewhere. Nor shall we draw any 

 definite line of distinction between gnats and moscjuitos. 

 It is often imagined that mosquitos are creatures confined 

 to warm climates and having nothing to represent them in 

 this country ; but the fact is that the difl'erence between a 

 gnat and a mos(iuito is little more than one ot name. To 

 an entomologist they are practically the same thing ; both 

 are members of the same genus, ( 'itlix. and the difference 



