252 



AN INTRODUCTION TO ENTOMOLOGY 



Fig. 276. — Tri- 

 dactylus apica- 

 lis. (From Lug- 

 ger.) 



smaller, the larger species measuring only 10 mm. in length; and the 

 hind femora are greatly enlarged, being strongly saltatorial (Fig. 276). 

 The antennae are short and composed of only eleven 

 segments. The fore wings are usually short and 

 never extend to the end of the abdomen; they are 

 horny, are almost veinless, and are not furnished 

 with stridulating organs in the male. The hind wings 

 are much longer, usually extending beyond the end 

 of the abdomen. The fore tibiae lack auditory 

 tympana. The first four tarsi, in our genera, are 

 two- jointed; the hind tarsi are one- jointed or want- 

 ing. The hind tibiae are furnished with movable 

 plates, "natatory lamellae," near the distal end; these 

 are ordinarily closely appressed to the tibia but can 

 be spread out like a fan. It is probable that these 

 plates are used to aid the insect in leaping from the 

 surface of water upon which they have jumped; 

 they may also serve a similar purpose on land, mak- 

 ing a firm planting of the end of the leg upon the 

 ground. The ovipositor is vestigial in our species; but Walker ('19) 

 states that in the exotic genus Ripipteryx there is a well-developed 

 ovipositor, which is remarkably similar to that of the short-horned 

 grasshoppers. These insects apparently have two pairs of cerci ; this 

 is due to the fact that in addition to the true cerci each of the two 

 podical plates is greatly elongated and bears a terminal segment, 

 which appears like a stylus or cercus. 



These insects burrow rapidly in sand and possess great powers of 

 leaping. They live on and in the damp sand on the shores of ponds 

 and streams. Their burrows extend only a short distance below the 

 surface of the ground. 



Only two genera, each represented by a single species, have been 

 found in America north of Mexico. 



Triddctylus. — In this genus the hind tibiae are furnished with four 

 pairs of long, slender plates, the "natatory lamellae;" and the hind 

 tarsi are one-jointed. Our species is Triddctylus apicdlis (Fig. 276). 

 Thejength of the body is 6-9.5 i^^n- 



Ellipes. — In this genus the hind tibiae are furnished with a single 

 pair of "natatory lamellse"; and the hind tarsi are wanting. Our 

 species is Ellipes miniita. The length of the body is 4-5 mm. 



Walker ('19) as a result of his studies of the genitalia of Ripi- 

 pteryx believes that the pigmy mole-crickets are more closely allied 

 to the Locustidae than they are to the Gryllidae, and ranks them as 

 constituting a distinct family, the Tridactylidse. 



Family LOCUSTID^* 

 The Locusts or Short-horned Grasshoppers 

 The family Locustidae includes the locusts or short-horned grass- 



*This family is termed the Acrididse by some writers, this name being based on 

 the generic name Acrida of Linnaeus; other writers use the family name Aery- 



