i34 INSECTS. 



is swimming about under the water ; but the air meanwhile is being used up in 

 breathing by means of the thoracic and abdominal spiracles. The beetles fly 

 strongly, and on fine summer evenings may sometimes be seen winging their way 

 to new quarters, a change which is often necessitated by the drying up of the pools 

 in which they had previously been living. Dytiscus marginalia, one of the largest 

 British species, is also one of the commonest and best known. Another common 

 species, Acilius swlcotus, is also represented in our figure. 



The Gyrinidai, or whirligig beetles, are a small but very well-defined group, and 

 in many points of structure are sharply distinguished from the other families of the 

 tribe Adephaga. In their oval shapes they resemble the Dytiscidw, though they are 

 usually somewhat flatter below and a little more convex on the upper side. But in 

 the relative proportions of the three pairs of legs they are 

 entirely different. The fore -legs are long and slender, and 

 when stretched out look like arms, whereas the two hinder 

 pairs are short and broad, being modified for use as paddles in 

 swimming. Another very distinctive feature is presented by 

 the eyes, each of which is divided by a ridge on the side of the 

 head into two widely separated portions, one lying on the upper 

 commos whirligig gjjy f ^he h eac i an d the other underneath. These beetles 



beetlk, Gyrinus . ...... 



natat&r (enlarged). appear, in consequence, to have four eyes ; one pair, as it is said, 

 though there is no proof of the fact, for espying objects above 

 them, the other for looking at things in the water below. From the Dytiscidai 

 and Carabidce they differ further in having their antennae shorter than the head, 

 and the outer lobe of the maxillae either completely atrophied or else in the form 

 of a slender spine. The Gyrinidoi, though widely distributed and represented in 

 almost all parts of the world, include altogether rather less than three hundred 

 known species. The genera are few in number and two only occur in Europe. 

 Some of the British species, such as Gyrinus natator, are commonly to be seen in 

 ponds and canals or " holes " in reedy sluggish streams, where the shiny little 

 beetles attract attention by the ease and rapidity of their movements as they skim 

 about on the surface of the water, performing a variety of intricate evolutions, 

 some sweeping along in graceful curves, others going round in circles or spiral 

 tracks, now all collecting together in groups, and then, if startled, suddenly darting 

 off with amazing speed in every direction. 



The next beetles we have to consider are those which, on account of their 

 abbreviated wing-cases, are known as the Brachyelytra. This tribe to which, 

 however, not all beetles with short elytra belong, contains a single very large 

 family — the Stapliylinidai. Owing to the shortness of their elytra, and the usually 

 narrow and elongated form of their bodies, the rove-beetles have an easily recognised 

 and characteristic appearance. The head is generally large and flat with a narrow 

 neck behind where it fits into the prothorax. The antennae — composed of eleven, 

 or occasionally twelve joints — are usually filiform, but are often slightly thickened 

 towards the extremity, and in some cases end in a distinct club. Though prominent 

 and conspicuous in a few genera, the eyes are, as a rule, raised but very little above 

 the general surface of the head. It is interesting to note that ocelli, which are of 

 such rare occurrence in adult beetles, are to be found in certain groups of this 



