But now listen; the honey dew does not come from the horns. On the end of some of the horns, or tubes, we can see a drop of clear liquid.
For a long time people believed this was honey dew, but instead, it is a waxy substance which is not sweet.
It has been very carefully studied by wise men who tell us it contains no sugar and is probably used as a means of defence, as aphides have been seen to smear the faces of insect enemies with this wax.
There are a great many species of aphides, and not all of them have the little tubes or horns on their backs. But probably many that have no horns give forth honey dew.
It is really a waste substance from the body of the aphid.
Ants are so fond of the honey dew that certain species of aphides have been called the ants' cows, because the ants take care of them for the sake of the honey dew.
Some ants protect the aphids from their enemies. They drive off those insects that would devour the aphids, and when winter comes these ants carry the aphids down into their warm nests under ground, and keep them safe through the cold weather.
The aphides cannot stand wet weather, but after a long spell of dry weather they will be found in great abundance.
Sometimes they eat so fast and so much that the honey dew falls like a shower from the trees upon which they are. It covers the ground beneath and the leaves of plants, and makes everything very sticky and disagreeable to the touch. The dust settles on it, too and a growth something like mould often turns it black—as we find to our discomfort.