Ciiap. X.] INSECTS. 337 



of these cases, as with the huge Dynastes and Megasoma, 

 we can at least see that there would be no necessity for 

 the males to be smaller than the females, in order to be 

 matured before them, for these beetles are not short-lived, 

 and there would be ample time for the pairing of the sexes. 

 So, again, male dragon-flies (Libellulidse) are sometimes 

 sensibly larger, and never smaller, than the females : 16 and 

 they do not, as Mr. MacLachlan believes, generally pair 

 with the females, until a week or fortnight has elapsed, and 

 until they have assumed their proper masculine colors. 

 But the most curious case, showing on what complex and 

 easily-overlooked relations so trifling a character as a 

 difference in size between the sexes may depend, is that of 

 the aculeate Hymenoptera ; for Mr. F. Smith informs me 

 that throughout nearly the whole of this large group the 

 males, in accordance' with the general rule, are smaller 

 than the females and emerge about a week before them ; 

 but among the Bees, the males of Apis mellifica, Anthi- 

 dium manicatum and Anthophora acervomm, and among 

 the Fossores, the males of the Methoca ichneumonides, 

 are larger than the females. The explanation of this 

 anomaly is that a marriage-flight is absolutely necessary 

 with these species, and the males require great strength 

 and size in order to carry the females through the air. In- 

 creased size has here been acquired in opposition to the 

 usual relation between size and the period of development, 

 for the males, though larger, emerge before the smaller fe- 

 males. 



We will now review the several Orders, selecting such 

 facts as more particularly concern us. The Lepidoptera 

 (Butterflies and Moths) will be retained for a separate 

 chapter. 



16 For this and other statements on the size of the sexes, see Kirby 

 and Spence, ibid. vol. iii. p. 300 ; on the duration of life in insects, see 

 p. 344. 



