Insect Epidemics 143 
parts of my house they lay in little heaps, just as they dropped 
from the nests above in the roof, and most of the nests were 
entirely depopulated. I examined some of the dead termites 
with a magnifier, but could detect no difference in them, 
excepting that they seemed a little swollen. 
That some epidemic prevailed amongst the insects there 
can be no doubt; and it is curious that it should have 
attacked so many different species and classes. Iam not sure 
that it was confined to the insects, for there was also a great 
mortality amongst the fowls, many dying from inflammation 
of the crop, and two large parrots fell victims to the same 
disease. This disease amongst the birds may not, however, 
have been connected in any way with that amongst the 
insects. I recollect that in 1865 there was a somewhat 
similar mortality amongst the wasps in North Wales. In 
the autumn of the preceding year they had been exceedingly 
abundant, and very destructive to the fruit. In the next 
spring, numerous females that had hybernated commenced 
making their paper nests, and I anticipated a still greater 
plague of wasps in the autumn than we had had the year 
before; but some epidemic carried off nearly all the females 
before they finished building their nests, and in the autumn 
scarcely a wasp was to be seen. I saw also in the Natural 
History magazines notices of their scarcity in all parts of 
England. 
The great mortality amongst the insects of Chontales in 
1872 has some bearing on the origin of species, for in times of 
such great epidemics we may suspect that the gradations that 
connect extreme forms of the same species may become 
extinct. Darwin has shown how very slight differences in the 
colour of the skin and hair are sometimes correlated with 
great immunity from certain diseases, and from the action of 
some vegetable poisons, and the attacks of certain parasites.} 
Any varieties of species of insects that could withstand better 
than others these great and probably periodical epidemics, 
would certainly obtain a great advantage over those not so 
protected; and thus the survival of one form, and the extinc- 
tion of another, might be brought about. We see two species 
1 Descent of Man, vol. i. p. 242; and Animals and Plants under 
Cultivation, vol. ii. pp. 227-230. Ihave taken the examples given from 
the same author. 
