1913.] 59 



THE WINGLESS GEOMETEE. 



BY JOHN H. WOOD, M.B. 



It is a remarkable circmnstance wlieu we come to tliiuk of it that 

 all the winter Geometers, without exception, have wingless females ; 

 but it is almost equally so that in so large a Division as the Geometrina 

 there is not, so far as I know,* a single British species that hibernates 

 in the perfect state. When we turn to the other great Divisions, we 

 find that in most of them there are hiberuators. Even among our 

 small number of Bhopalorera there are several that do so ; quite a 

 number in the Noctidna, and the same also in the " Micros," both 

 Tortricina and Tineiim. There must then be something peculiar 

 either in the constitution or the structure of the Greometer to account 

 for the fact that none of them hibernate. This something I think we 

 can find in the structure of the wing. These organs are very large for 

 the size of the insect; they are also by comparison very weak and 

 flimsy, and they are, besides, disposed at rest in a very open and 

 exposed manner. On the other hand, in two of the great Divisions 

 mentioned above, the structure of the wing is stronger, the size less 

 ample, and at rest they are carried close to the body. In the other 

 great Division, the Bhopalocera, the wings, though ample, are reduced 

 to half their size by meeting over the back when the insect is at rest, 

 and at the same time in this position each supports and strengthens 

 the other. Hence these insects can creep into small chinks and 

 cavities, or shelter among leaves and rubbish without risk to the 

 wiiigs, organs of such importance when the awakening season arrives. 

 But the case is very different with the Geometers. Small chinks and 

 crannies are not available for them with their ample wings, whilst 

 should they seek shelter among diy leaves or rubbish, these tender 

 organs would get sadly frayed and tattered. 



The same difficulty, to a large extent, must meet the winter 

 Geometer. Its wings are an incumbrance and an impediment. There 

 are no leaves under which the insect can take shelter, and the tree 

 trunks, common resting places in the summer, deprived of their leafy 

 covering become in a rainy time watercourses, collecting on all sides 

 the streams running down from the boughs. And so it has come 

 about, in the interest of the species, that the female who has to live 

 considerably longer than the male, and never goes in search of him, 

 but he of her, loses her wings, whilst her mate retains them in full 

 perfection. Probably all of us who have given any thought to the 

 matter have come to much the same conclusion. 



* Except Triphosa duhitata, Cidaria miata, and C. psittacata. — J. J. W. 



