August 1, 1S66.] 



SCIENCE-GOSSIP. 



183 



"WATER-BEETLES. 



HAVING recently bad in my possession a large 

 aquarium stocked with several species of 

 common British water-beetles, I have had consider- 

 able opportunity for watching their various actions 

 and habits ; among which the activity which they 

 display in chasing and fixing on their prey, and 

 their extreme voracity, are certainly the most re- 

 markable. To the Dytiscus marginalis nought seems 

 to come amiss ;lfor fish, newts, small frogs, and even 

 fresh-water snails, all share the same fate when 

 placed within the reach of this ravenous and power- 

 ful insect. It frequently kills more than it is able 

 to consume, and when it has succeeded in destroy- 

 ing every living object not belonging to its own 

 species, it will, without hesitation, fall upon those of 



Fig. 1/2. Water- Beetles {Dytiscus marginalis). 



its own relatives which may happen to be confined 

 with it. Indeed, sometimes the battles between 

 them are of a most furious and savage nature. The 

 poor newt is obliged to succumb without much re- 

 sistance ; for when its deadly enemy once obtains a 

 hold, all its endeavours to shake it off are entirely 

 useless. I have seen a Triton cristatits covered with 

 as* many as three or four of these insects, besides an 

 equal number of the Acilius sulcatits at the same 

 time, whilst the hapless reptile swam and dashed 

 about the water in the highest state of discomfiture, 

 and, being unable to release itself, was obliged at 

 last to yield to the strong mandibles of its adver- 

 saries. It is even difficult to separate their prey 

 from them, so tightly do they cling to their victims. 

 The Notonecta, or common boat-fly, is also exceed- 

 ingly voracious, even darting at and seizing upon 

 the point of a penknife when presented to it whilst 

 lying close to the surface of the water. If a small 

 earthworm be suspended from the end of a piece of 

 thread, and be placed close to any of the insects 

 I have mentioned, it will be almost instantly attacked; 

 and such is the tenacity with which they adhere to 

 the bait, that they may be easily drawn out of the 

 water. This is, in fact, a capital method of catching 

 them in the first instance, as the thread can be 



annexed to the end of a long stick or fishing-rod, 

 for they are not to be easily captured by means of a 

 hand-net, on account of their .quick movements 

 when disturbed, especially if they are seen at some 

 distance from the side of the pond in which they 

 are to be found. Although these insects are able to 

 devour an immense quantity in proportion to their 

 respective sizes, still if a single specimen be kept 

 by itself, it will subsist for a considerable period 

 without any food at all. As almost all water-beetles 

 are of this voracious disposition, they must not, of 

 course, be introduced into an aquarium in which 

 fish, &c, are kept ; but when in solitary confine- 

 ment, and properly fed, they form very interesting 

 and amusing objects. J. H. Eox. 



The Black axd Brown Bats. — The black rat, 

 which has become more and more rare, is disappear- 

 ing daily from the continent of Europe, in conse- 

 quence of a revolution, not less bloody, though less 

 generally known, than those which the barbarians of 

 the North brought in former times upon the empires 

 of the more civilized world. Eor ages the mouse, 

 which was the only representative of this family 

 known to the ancients, hved at our expense, with 

 no enemy to fear in its quasi- domestic state, save 

 man, whom it pillaged, and the cat, which the lords 

 of the creation had called to their aid against an 

 adversary which had been rendered formidable by 

 its very diminutiveness and timidity. During the 

 middle ages, the black rat, coming no one knew 

 from whence, spread itself over Europe and attacked 

 the mouse, who, too feeble to resist his ferocious 

 antagonist, was obliged to share with him his old 

 haunts, only escaping complete destruction by re- 

 tiring within his narrow galleries, whither the 

 enemy could not pursue him. At the beginning of 

 the last century, the Norway, or brown rat, brought 

 by merchant vessels from India, appeared in Europe, 

 and at once began to wage an exterminating war 

 against the black rat. Its greater strength, ferocity, 

 and fecundity, enabled it rapidly to gain ground. 

 This rat first appeared in England in 1730 ; twenty 

 years later it was observed in Erance ; but at the 

 period when Buffon wrote his immortal work, it was 

 only met with in the environs of Paris, and had not 

 yet penetrated to the city. At the present day it is 

 the only rat met with in the capital, and in the 

 greater part of the provinces. Its partiality for 

 the water, and the readiness with which it swims, 

 have enabled it to follow the courses of rivers, and 

 by ascending the smallest affluents, it has contrived 

 to diffuse itself over the whole country. It has 

 driven the black rat before it, exterminating it in 

 many of our provinces, and forcing it to take refuge 

 in mills or isolated farms. — Quatrefages' Rambles of 

 a Naturalist. 



