532 NATURAL HISTORY OF ARTHROPODS. 



middle tibisB have a single spine. The larva is short and stout, and usually spins a 

 dense brown cocoon. In habits, the group contains sand diggers, hard clay diggers, 

 wood borers, species which excavate the pith of twigs, and species which adapt the 

 old nests of many species of wasps. The genus Trypoxylon is particularly notice- 

 able from its habit of adapting the old nests of other species to its own purposes. 

 Trypoxylon albitarse is found abundantly in old cells of Pelopceus in the western 

 states, reprovisioning them with spiders. The South American 2\ fugax fills with 

 clay the cells of a nest of Polistes, and the European T.figulus enlarges the burrows 

 of wood-boring species. Any convenient tubular hole will be used by these insects, 

 which thus make use of the cavities of straws, and of rose twigs from which the pith 

 has been excavated by some Crabro or Rhopalum. The genus Rhopalum bores 

 extensively in pithy stems. It. pedicellatum has been bred from the stems of rose, 

 Corcoriis, Japonica, and Spiraea in New York. The species of the genus Crabro are, 

 in the main, wood-borers. C. singularis and C. sextnaculatus are both American 

 species which have this habit. Crabro patellatus of Europe, however, burrows in the 

 sand and provisions its nest with Diptera. Crabro tibialis bores, like Rhopalum., into 

 the pith of brambles and roses, and its nests are destroyed by the parasitic chrysid, 

 Hedychrum ardens. The genus Oxybelus is composed of small, dark, active insects, 

 usually with white-spotted abdomens. The female captures her prey, which consists 

 of dipterous insects, in much the same way as does Mellinus. Alighting upon a 

 sunny, grassy spot, she moves slowly around until the flies have become accustomed 

 to her presence, when, with a sudden spring, she seizes a victim and bears it away in 

 triumph. 



The family Vespid^ includes the insects known as the " true wasps " in contra- 

 distinction to "sand-wasps," "wood-wasps," and other similar terms applied to the 

 fossorial Hymenoptera. The true wasps may be distinguished from other Hymen- 

 optera by the longitudinal folding of the wings when at rest. The antennas are 

 elbowed, and consist of twelve joints in the female and thirteen in the male. The 

 labium is quadrilobed, or sometimes only bifid, each of the divisions being glan- 

 dular at tip. The eyes are lunate. The abdomen is sometimes sessile and sometimes 

 petiolate, and is composed of seven segments in the male and six in the female. 

 The female is furnished with a retractile sting. The legs are slender, and are not 

 hairy. The wings always present two recurrent nervures, and three or four sub- 

 marginal cells. Both sexes are always winged. The body is either naked or 

 slightly clothed with hairs. It is usually black in color, usually more or less spotted 

 with some shade of yellow. 



The true wasps vary greatly in habit. Some species are parasitic ; others are soli- 

 tary, living by rapine ; while the higher forms are social. These three peculiarities of 

 habit are correlated with structural peculiarities, so that the division of the family 

 into three groups characterized by habits corresponds to the natural division into 

 three sub-families based upon structure. These three sub-families are the Masarinse, 

 or parasitic wasps, the Eumeninae, or solitary wasps, and the Vespinee or social 

 wasps. 



In the sub-family Masarinse the fore wings have only three submarginal cells, two 

 of which are closed, the eyes are but slightly notched, and the wings are indistinctly 

 folded. These insects are mostly tropical, but four or five being known in South 

 Europe. In America the group is represented only by the genus Masaris, and the 

 species all come from the extreme west. 



