180 . INSECTS. 



length of the body, the tarsi are three-jointed, and the female always has a very 

 short ovipositor. They differ also in the position of the auditory organs, and in 

 the mode by which the males produce the chirping. In these insects the organs of 

 hearing appear externally as two pits, somewhat crescentic or semilunar in shape, 

 placed one on each side of the first abdominal segment, immediately behind the 

 thorax. At the bottom of each pit there is a tense membrane, which on its inner 

 side is brought into relation with the terminal rods and fibres of a nerve which 

 arises from the last thoracic ganglion. It was thought that these pits were in some 

 way concerned in the production of sound, but it is evident from their structure 

 that this is not the case, while they really seem capable of serving no other function 

 than that of ears. Moreover, it is now known that the chirping of these insects is 

 produced by rubbing the hind-legs up and down against some of the projecting 

 nervures in the sides of the closed elytra. When the insect is stridulating it keeps 

 the tibia of the leg folded up against the femur. In some species the sound is 

 heard at both the upward and downward stroke of the legs, in others at the 

 downward stroke only. The sound varies in intensity in different species, and for 

 this reason some of the commoner species may be recognised even before they are 

 seen. In most of these insects the front of the head is vertical, or slightly inclined 

 backwards, but in some (Tryxalince) it is much inclined backwards, and the whole 

 head seems prolonged in a way that makes it look like a cone or wedge, with the 

 antennas and eyes near the apex, and the mouth placed below under its base. The 

 Acridiidce are usually provided with three ocelli in addition to the compound eyes, 

 the ocelli being as a rule more distinct than in the Locustidce. The mouth-organs 

 are well developed, consisting of a large upper lip ; strong, toothed masticatory 

 jaws ; five-jointed maxillary palpi ; and a lower lip, divided at the end into two or 

 four lobes, and bearing three-jointed palpi. The prothorax is generally large, 

 much longer above than below, and often carrying a prominent crest along the 

 middle. Wings are usually present, but the hind-pair are wanting in the females, 

 or even in both sexes, of some species. In their general life-history the Acridiidce 

 are probably much alike. The female lays her eggs at a short depth below the 

 surface of the ground, or attaches them to the stalks of grasses, and usually 

 surrounds them, in mass, with some sort of protective covering. Later on in the 

 same year, or in the spring of the year following, the larvse are excluded. They 

 soon become active, and — except that they are without wings, have shorter antennse, 

 and are of smaller size and no definite colour — do not differ much in appearance 

 from the perfect insects. After undergoing, as a rule, about six moults, the larvae 

 which are hatched in the spring become adult late in the summer. It is generally 

 in the days immediately following their entry into the perfect state that the male 

 insects are loudest and most persistent in their song. Few of the British Acridiidce, 

 of which there are about a dozen, are remarkable for the brightness of their colours ; 

 nor do any cause trouble by a great excess of numbers. But amongst the exotic 

 species there are many exhibiting vivid tints of colour ; and some which are 

 capable of multiplying to such an extent as to become a serious source of mischief 

 in the places where they abound. It is to the species accustomed to assemble 

 together, and migrate from place to place, in vast swarms, that the name of locusts 

 is more especially applied ; this habit really constituting almost the only difference 



