Mr, CuRTls's Ohj creations on jlphiJea, 8^ 



and imiformly; whoreas its appearance is extremely irregular, not 

 alike on any two leaves of the lame tree or plant, iome having none 

 of it, and others being covered with it but partially. 



But thephasnomena of the honey-dew, with all their variations, are 

 eafiiy accounted for by confidering the Aphides as the authoi's of it. 

 That they are ca}>able of producini^ an appearance exa6lly fimiiar 

 to that of the honey-dew, has already been (liown. As far as my 

 obfervation has extended, theuc never exifls any honey-dew but 

 where there are Aphides ; fuch, however, often \>\\h unnoticed, 

 being hid on the under fide of the leaf. Wherever honey-dew is 

 obfervable about a leaf, Aphides will be found on the under fide of the 

 leaf or leaves immediately above it, and under no other circumlhinces 

 whatever. If by accident any thing fliould intervene between the 

 Aphides and the leaf next beneath them, there will be no honey- 

 dew on that leaf. Thus then we tl^ttcr ourlclves to have incontro- 

 vertibly proved that Aphides are the true and only Iburcc of tiic 

 honey-deu\ 



We have found that where the faccharine fubftance has dropped 

 from Aphides for a length of time, as from the Aphis falicis in 

 particular, it gives to the furface of the bark, foliage, or whatever 

 "it has dropped on, thatfooty kind of appearance which arifcs from 

 the exploiion of gun-powder, which greatly disfigures the foliage, &c. 

 of plants. It looks like, and is fometimes miftak<fn for, a kind of 

 black mildew. We have fome grounds for believing that a faccha- 

 rine fubftancc, finiilar to that of the Aphis, diops from the Coccus 

 aUo, and is finally converted into the fame, kind of powder. 



In moft feaions the natural enemies o'i the Aphiaes ar-e fufFicient 

 to keep them in check, and to prevent them from doing any e (Ten- 

 tiul injury to plants in the open air. But feafons fometimes occur^ 

 very irregularly indeed, on i:n average, perhaps, once in four or fix 

 years, in which they arc multiplied to fuch an exctfs, that thte 



M t ufuai 



