social insects, can be seen any bright day in
August or September busily engaged on the margins of ponds, ditches, and
puddles in the procurement of building materials. They will alight close
to the water's edge, and, vibrating their wings rapidly, will run hither
and thither over the moist clay until they arrive at a spot which, in
their opinion, will furnish suitable mortar. Quickly biting up a pellet of
mud, they moisten it with saliva, all the while kneading it and rolling it
between maxillae and palpi. When it has reached the proper consistency they
bear it away to some dry, warm place, such as the rafters of an outhouse
or a garret, and there use it in the construction of their adobe or mud
nests.

There may be dozens of these nests in the process of construction, and
arranged on the rafters, side by side, yet these busy little masons
never make the mistake of confounding the houses; after securing mortar
they invariably return, each to her own structure. This statement can be
easily verified. While the insect is engaged in applying the mortar,
take a camel's-hair brush and quickly paint a small spot on her
shoulders with a mixture of zinc oxide and gum arabic; then mark the
nest. The marked wasp will always return to the marked nest.

As soon as the cells are completed, the wasp deposits an egg in each,
and immediately begins to busy herself about the future welfare of the
coming baby wasps. Just here these remarkable creatures show that they
possess a mental faculty which far transcends any like act of human
intelligence; they are able to tell which of the eggs will produce males
and which females. Not only are they able to do this, but, seemingly
fully aware of the fact that it takes a longer time for the female larvae
to pupate than it does the male larvae, they provide for this emergency
by depositing in the cells containing female eggs a larger amount of
food. It is in the procurement and storage of this food-supply that
these insects give unmistakable evidence of the possession by them of
the faculty of computing.

The knowing little mother is well aware of the fact that as soon as the
egg hatches the young grub will need food, and an abundance of food at
that; so, before closing the orifice of the cell, she packs away in it
the favorite food of her offspring, which is spiders. She knows that in
the close, hot cell the spiders, if dead, would soon become putrid and
unfit for food: therefore, she does not