224 THE GREAT WATER-BEETLE. 
spiny thighs against their rigid wings ; and this ache* 
rontia atropos appears to produce the noise it at times 
makes, which reminds us of the spring call of the rail 
or corncrake, by scratching its mandible, or the instru- 
ment that it perforates with, against its horny chest. 
The object of this noise is apparently a mere sexual 
call. Heavy and unwieldly creatures, they travel badly, 
and from the same cause fly badly and with labor ; and 
as they commonly hide themselves deep in the foliage 
and obscurity, without some such signal of their pres- 
ence a meeting of the parties would seldom be accom- 
plished. 
Another of the ravenous creatures that infest our 
pools is the great water-beetle (ditiscus marginalis) ; 
and perhaps it is the most ferocious of any of them, 
being adapted by every provision for a life of rapine, 
endued with great muscular power, armed with a thick 
and horny case over its body, and having its eyes large 
to observe all the creatures about it, and powerful man- 
dibles to seize and reduce them to fragments. It riots 
on the polyphemus of the pool ; and having thinned its 
herd in one place, is supplied with wings to effect a 
removal to a fold better furnished. It even eats the 
young of the frog ; and its bite is so powerful, as to be 
painfully felt by the hand that holds it a captive, though 
defended by a glove. In the larvae state it is almost 
equally destructive ; it swims admirably ; its hinder 
legs are long and brawny, beside being aided by a 
fringe of hairs, so that they are powerful oars to propel 
its body with celerity and ease. Nor must we omit a 
peculiarity attending the constitution of this beetle, 
which marks it as as a creature especially endowed for 
the station in which it is placed. Multitudes of insects 
exist in the larva state for a certain space of time in 
water, and, having accomplished a given period in this 
state perfecting their forms, they take wings and be- 
come aerial creatures, after which a return to the ele- 
ment whence they sprang would be death to them. But 
this beetle, when it has passed from the larva state and 
obtained its wings, still lives in that water which nour- 
ished it to this state of perfection, without any incon- 
