98 AN INTRODUCTION TO ENTOMOLOGY. 



her of these is of use in distinguishing species ; and the presence or 

 absence of the last spine in the outer row is of much greater impor- 

 tance. Besides these spines there are four articulated spurs, which 

 are situated in two pairs, one on the outer and one on the inner 

 side of the tibia. The sexes can be easily distinguished. In the 

 males the ventral surface of the abdomen consists of nine segments, 

 while in the females there are but eight. The caudal end of the 

 body in the females is furnished with four horny appendages, the 

 ovipositor; in the male the ventral pair of appendages is repre- 

 sented by a single plate. 



With many species of the Acrididse we find the males furnished with strid- 

 ulating organs. These are not nearly so highly developed as those of mem- 

 bers of the two higher families, and are used only in the day-time. The 

 Locusts stridulate in two ways. Certain species rub the inner surface of the 

 hind legs against the outer surface of the wing-covers. With these insects 

 there is a thickening of one of the main longitudinal veins in the centre of the 

 wing-cover (vena radidlts), and a remarkable extension of the two areas be- 

 tween this vein and the costal margin of the wing-cover (area s'capuldris and 

 area externomedid), which serves as a sounding-board, and which is wanting in 

 the female. The most common representatives of the insects which stridulate 

 in this way belong to the genus Stenobothrus. According to Scudder, the 

 Stenobothri, when about to stridulate, place themselves in a nearly horizontal 

 position, with the head a little elevated ; then they raise both hind legs at 

 once, and grating the femora against the outer surface of the tegmina, produce 

 notes which in the different species vary in rapidity, number, and duration. The 

 first one or two movements are frequently noiseless or faint; and when the 

 sky is overcast, the movements are less rapid. Scudder has recorded the 

 songs of several species by means of a musical notation.* 



The second method of stridulation practised by locusts is by rubbing 

 together the upper surface of the front edge of the wings and the under sur- 

 face of the wing-covers. Those which employ this method stridulate during 

 flight. Several common species pertaining to the CEdipodinae will serve as 

 illustrations : Chimarocephala viridifasctata, Eucoptolephussordidus, and Dissos- 

 teria Carolina. Certain other closely allied species produce no sound whatever. 



Locusts lay their eggs in oval masses, covered with a tough glutin- 

 ous secretion. Many species deposit them in the ground, the ovi- 

 positor of the female being well adapted for making the necessary 

 hole. The tips of the four horny appendages of which it is com- 

 posed can be alternately applied together and spread apart ; in this 

 way it is an easy matter to force the earth aside and press the end of 

 the abdomen into the ground. Fig. 97 represents the Rocky Moun- 



* Proc. Bost. Soc. Nat. Hist., vol. XL 



