40 Sir G. S. Mackenzie's Notices of Insects, dfc. 



caterpillars took the form of pupae ; and it is probable that 

 the nature of this particular insect is such that it continues in 

 that form perhaps longer than a century. To suppose that 

 this is the case seems to me more natural, as it is more con- 

 formable to analogous facts, than to suppose that the ova con- 

 tinues so long;. There were no circumstances, such as the 

 stirring of the soil, which could have brought the ova into 

 a condition to live ; and the simultaneous appearance of the 

 insects in different parts of the country, and their ravages be- 

 ing limited to a certain breadth, make it probable that the in- 

 sects, after their usual long period, had issued from the earth, 

 ascended the trees, deposited their eggs, and died. The pu- 

 pa? into which the host of caterpillars passed are now proba- 

 bly in the earth under the trees, and from them a new host 

 will at length arise, more numerous perhaps than the last. 

 If it should happen that the trees shall have been removed 

 before the pupae shall have become perfect insects, no proper 

 food will be found for their progeny, which will perish. It is 

 probably this circumstance that saves much that we value from 

 destruction ; the proper food of insects being removed from the 

 place where the pupae are concealed. Of course, this does 

 not limit the wanderings of migratory insects, but many 

 even of these must perish, while in search of a proper place 

 for their ova. 



This season, there is an amazing number of aphides. 

 There is scarcely a vegetable without its aphis. There has 

 been a most luxuriant harvest for the bee tribe on the thorn 

 hedges, which are loaded with the honey-dew, the produce of 

 the aphis, which the bees greedily devour. The foliage of 

 the birch has suffered severely from the attacks of an aphis. 

 Even the strawberry has had its variety ; but it was only on 

 some plants which I forced on which I observed it. There 

 is an aphis which we have every year on the spruce-fir, which 

 forms a very beautiful nidus on the young shoots, resembling 

 a small seed-cone, for which it has often been mistaken. The 

 silver and the balm of Gilead firs have been killed in great 

 numbers by the attacks of a woolly aphis, like that which in- 

 fests the larch, and it attacks the bark in the manner of the 

 apple aphis. 



