26 
alarmed drop to the bottom of the fen and sham death. They fly very 
little after dark. The $ is very rarely met with, and seems to sit 
about on the rushes, and seldom flies. 
Habitats: 1 ’he insect is very local, even in its favourite haunts, 
which are lens and rushy meadows, and it seems to keep to the rushy 
patches in the broads, and not to be all over the fen. Mr. Prout tells 
me he has taken the species in the Isle of Wight, where there is a 
small trickle of water down the dill, with a few reeds and rushes 
growing in it, the whole spot being only a few feet square. It occurs 
throughout Britain towards the end of July. 
Parasites : The following parasites were bred from the larvie: 
Barichnenmon lepiilus, Aritranis rami few, and Bracon fulcipes. 
Variation : The perfect insect varies a good deal, and in addition 
to the forms mentioned in Brit. Nnct., vol. i., p. 48, viz., (1) the type 
(2) ab. lineola, Stph., (8) ab. pallescem, Tutt; there is (4) an interest¬ 
ing reddish-brown form = ab. fiisca, Bankes. 
I am indebted to Mr. Main for the photographs. 
DISCUSSION AS TO CAUSE OF OCCASIONAL ABUNDANCE OF A 
SPECIES FOLLOWED BY SCARCITY IN ENSUING YEARS. 
(Opening remarks by Dh. T. A. CHAPMAN, F.E.S., March 16tli, 1909.) 
I must claim your indulgence for the crudeness of the few remarks 
I propose to make ; the gross defects, in fact, are only to be excused, 
if you can find it possible to excuse them, on the ground that this is 
not a paper, but merely a stop-gap. I should not have ventured to 
submit this communication as a paper to be entered in the programme 
of the Society. The chief defect, a serious one from a scientific point 
of view, is that I ask you to take the data, in some degree, for granted, 
for the rest, to supply them yourselves. In fact, one of my objects is, 
if possible, to get you to supply these data from your own observations 
or from other sources. I believe that I have met with, both in reading 
and in written and oral communications from many friends, the data 
I assume, but not always in more than detached observations instead 
of completely verified detail. 
Insects, and especially lepidoptera, perhaps more than other 
animals, vary very much from year to year in the number of individuals 
that exist. As a rule, the fluctuation in numbers is restricted within 
moderate limits, but every now and then some particular species over 
a larger or smaller area is found to be excessively abundant. 
This abundance is associated, if my memory of what I have read 
and heard be at all trustworthy, not infrequently with two other 
circumstances. One is, that variation is more common amongst such 
swarms than in ordinary years, not variation in the direction of 
extreme and remarkable aberrations, but in the presence of many 
specimens that deviate somewhat from the type, specimens that are 
not remarkable, but nevertheless are not common in ordinary years; 
the other is, that such years of plenty, when one would expect that in 
xix. 
