20 
was as fine, the wind in the same quarter, but I never saw a specimen. 
At other times they will come out at intervals for, perhaps, over an 
hour, and not appear in large numbers at all, this is what might be 
expected, but their sudden appearance in enormous numbers, and equally 
sudden disappearance, or their absence on apparently suitable nights, are 
not very easy to explain. A third item that has puzzled me is that 
when sweeping the herbage, when I have often taken them in cop. I 
have twice found a second female in the net, as though she had been 
attracted to the male after he had paired with another. From one of 
these females I obtained eggs that proved infertile. In these two 
species the manner of flight is the same : the males swinging backward 
and forward till they attract the females, the one by sight, and therefore 
flying in an open and exposed place, and being light and shining ; the 
other by scent, the diffusion of which is assisted by the motion, and 
the insect, therefore, flying in a sheltered nook where the faint odour 
is not lost. Should the scent-producing power of hectus ever be lost, 
either entirely, or at some particular locality, a result might be expected 
like that which has already been obtained in humuli. The specimens 
most easily seen, those, for example, with more silver on their wings, 
would be more easily observed by the females, would be more certain 
to secure partners, and would tend to produce a more silvery race, 
which in always increasing ratio, would go on until males were pro¬ 
duced entirely silver on both wings, like those of humuli. Specimens 
of hectus, with faint traces of silvery markings on the hind wings, are 
not very uncommon, and they occasionally occur with the spots well 
defined. With the tendency for the silvery markings to become larger, 
another factor would also come into operation. As the female would 
require to see the male, it would follow that, the larger the specimen, 
the more easily would it be seen. Thus the larger males, also, would 
be more certain to find partners, and produce larger offspring, this 
double action constantly at work, hectus would both increase in size 
and become more and more suffused with silver, until an insect would 
eventually be evolved, not only silvery like humuli , but as large in size. 
It is not difficult, therefore, to see how two species may spring from 
one ancestor. 
The males cf the other three British species of this genus fly in a very 
different manner to those already spoken of. Lupulmus is much the 
commonest species of the three, and the males may be seen hunting 
for the females in early twilight with a most erratic flight just above the 
herbage, darting hither and thither, turning and twisting about in all 
directions and with great rapidity. Common as the species is, and 
closely as I had watched it for some years, I never saw the act of pairing 
till last summer. This was described in detail in the E.M.M ., vol. 
xxvii., p. 197, and I had better quote the account written at the time, 
than re-describe from memory. “On the evening of June 3rd (1891), 
I saw a newly emerged female crawling up a grass stem. It was just then 
eight o’clock; and at the same moment a male approached with its 
usual rapid, irregular flight. It flew within a foot of her, but did not 
take the slightest notice, and was evidently unconscious of her 
proximity. When she was half-way up the stem she commenced to 
vibrate her wings; first there was a preliminary flutter or two, and then 
a steady, long-continued vibration, which lasted without intermission 
for ten minutes. A male then approached. It flew in its usual quick 
