930 



INSECTA. 



nervura of the inferior wing, and is received 

 into a socket near the base of the main nervure 

 on the under side of the upper wing. This 

 apparatus for connecting the wings appears to 

 give additional strength to the insect, since it 

 exists only in those species which fly most 

 rapidly, and continue for a great length of time 

 on the wing. But in those insects in which 

 the body is very large in proportion to the 

 size of these organs, and which are necessitated 

 by their habits to be constantly abroad, and to 

 fly to a great distance, as is the case with the 

 Hymenoptera, the means of uniting the wings 

 is more perfect. It consists not of a single 

 booklet, as in Lepidoptera, but of a series of 

 very minute hooks of a somewhat spiral form 

 (Jig. 397), and arranged along a curved portion 



Fig. 397. 



A, inferior wing of Bombus terrestris ; a, the 

 costal nervure, on which are seated the hooks, b ; 

 (c, the winglet) ; B, the hooks in the working bee, 

 apis metttftca. 



of the costal nervure, at the anterior superior 

 margin of the second pair of wings. These 

 hooks are described by Mr. Kirby,* and are 

 found in nearly all the Hymenoptera. They 

 are arranged in a slightly twisted or spiral 

 direction along the margin of the wing, so as 

 to resemble a screw, and when the wings are 

 expanded attach themselves to a little fold on 

 the posterior margin of the anterior wing, along 

 which they play very freely when the wings are 



* Monographia Apum Angliae, vol. i. tab. 13, 

 fig. 19. Ipswich, 18U2. 



in motion, slipping to and fro like the rings on 

 the rod of a window curtain. The form of 

 the hooks is very similar throughout the whole 

 order, each hook being twisted at its extremity 

 a little to one side and recurved. They are 

 always situated at the same part of the wing, 

 but vary in number in different genera, and 

 even in the sexes. In Urocerida, Slrex juven- 

 cus, they are few and scattered along the margin 

 of the wing, and this is also the case in Tri- 

 chiosoma, but we have found them far more 

 numerous in Ichneumon Atropos. In the 

 sterile fema?2 or worker of the common wasp, 

 Vespa vulgaris,\ve have found them very strong, 

 and about twenty in number, besides five stiff 

 spines which are not bent in the form of hooks. 

 In most instances, particularly in the Bombi, 

 the hooks are less numerous in the males than 

 in the females. Thus, in the male of Bombus 

 terrestris there are but eighteen in each wing 

 in the male, but twenty-five in the fertile 

 female. In the male of Bombus lapidarius 

 there are only eighteen in each wing, and there 

 is the same number in the worker or sterile 

 female, but there are twenty-three in each wing 

 of the fertile female. In Anthophora retusa there 

 are only twenty in the male, but twenty-two in 

 the female. In Osmia there are twelve in the 

 male and fifteen in the female. But the reverse 

 is the case in Anthidium manicatum, in which 

 there are thirty in the male, but only twenty- 

 five in the female. In Megachile there are 

 sixteen in the female, but in the cuckoo-bee, 

 Melecta punctata, there are thirteen hooks and 

 four imperfectly developed spines. In the 

 male of Eucera longicornis there are only 

 thirteen hooks, but in the female twenty-three, 

 while in the female Calioxys conica there are 

 only twelve. In the queen or fertile female of 

 the common hive-bee there are only seventeen 

 slender hooks, arranged at some distance apart, 

 and different in their appearance from those of 

 the common humble-bee. In the sterile female 

 or worker there are nineteen, but in the heavy 

 male, or drone, there are twenty-one. In the 

 male, as in the fertile female, of the hive-bee, 

 the hooks are placed further apart, and are more 

 slender than in the workers, besides which they 

 are differently shaped in the neuter, in which 

 each hook has also a little tooth near its apex. 

 On reviewing this difference in the number of 

 hooks in the two sexes, we are certainly con- 

 firmed in the opinion that it has some relation 

 to the comparative powers of flight of the 

 respective insects, and is not a sexual distinc- 

 tion. The great object of the hooks evidently 

 is to keep the wings steady during flight, in 

 order that they may act in unison, and thereby 

 enable the insect to continue much longer on 

 the wing with less muscular exertion, because, 

 when the two wings are made to act but as one, 

 the effort of flying becomes more concentrated, 

 and the wings strike the air with greater effect 

 than if they were separated or but imperfectly 

 connected. It is well known that the males of 

 the humble-bees, Bombi, are much feebler on 

 the wing than the fertile females, and it is the 

 same with the individuals of the genus Osrnia, 



