little round pads thickly covered with downy hair. On each
side are two sharp claws and many stiff, clinging hairs. With this
flattened foot it can go wherever it wishes.

"But this same little foot is the chief reason why a fly should never be
allowed in the house, for flies crawl into all sorts of dirty places,
and the fine hairs catch and hold the dirt. When the fly lights on us
or on the table, some of the pieces of dirt are shaken off."

"But they are so hard to catch," said Betty; "it takes Lizzie forever
and forever to get them out of the dining-room in the morning."

"I know why they are hard to catch," added Jack, "for I've looked at a
dead fly. They have such big eyes, like lighthouses, they can see all
around."

"Yes," said Ben Gile; "there is no such thing as creeping up on a fly
unawares. Flies are dirty creatures," continued the old man, "and the
time is not very far distant when people will make war on them just as
they do on mosquitoes. Mrs. Fly lays her eggs in unclean places, and as
many as a hundred eggs at a time. These eggs hatch out quickly. It takes
only twenty-one days to make a chicken out of an egg, but to make a baby
fly it takes only a few hours, and ugly babies they are--little white
maggots, or worms, that live and feed and grow rapidly in dirty places.
Within six days the maggot becomes a tiny, dark-brown pupa, and after
five days the pupa hatches out into a grown-up fly."

A dozen little girls at the party made up their minds promptly that
after this evening they, at least, would make war on flies.

"And aren't flies of any use?" asked Betty.

"There is one little fly, Mrs. Tachina-Fly, who is of some use. She is a
cousin of the house-fly. She is of use because she chooses a queer place
to lay her eggs--on the back of a young caterpillar. After these
caterpillars grow and shut themselves up into a cocoon to change into a
butterfly the little fly eggs hatch out into maggots. Of course they are
hungry--all babies are; and finding the nice, fat caterpillar in the
round house, like dutiful babies they eat what is set before them until
the fat, tender caterpillar is eaten up. After they are satisfied they
lie still in their brown skins and change into grown-up tachina-flies,
and at last out come a lot of busy, _buzzing_, bothersome flies. It is
rather hard on the caterpillar. But when we think what harmful, greedy
things most caterpillars are, perhaps it is good that there are
tachina-f