Several species of flies are found commonly in houses. Some of them so
closely resemble the true house fly that it requires very careful
observation to distinguish them from it.
One of these is the biting stable fly[2] (fig. 1). It occurs frequently
in houses and differs from the house fly in the important particular
that its mouth parts are formed for piercing the skin. This fly is so
often mistaken for the house fly that most people think that the house
fly can bite.
Another frequent visitant of houses, particularly in the spring and
fall, is the cluster fly.[3] It is somewhat larger than the house fly,
and is distinguished by its covering of fine yellowish hairs.
Occasionally this fly occurs in houses in such numbers as to cause great
annoyance. It gets its name of "cluster fly" from its habit of
collecting in compact groups or clusters in protected corners during
cold periods.
Several species of metallic greenish or bluish flies also are found
occasionally in houses. These include a blue-bottle fly,[4] the black
blowflies,[5] and the green-bottle (fig. 2) flies.[6] They breed in
decaying animal matter.
[Footnote 1: _Musca domestica_ L.]
[Footnote 2: _Stomoxys calcitrans_ L.]
[Footnote 3: _Pollenia rudis_ Fab.]
[Footnote 4: _Calliphora erythrocephala_ Meig.]
[Footnote 5: _Phormia regina_ Meig. and _P. terrae-novae_ Desv.]
[Footnote 6: _Lucilia caesar_ L., _L. sericata_ Meig., and other species
of the genus.]
There is still another species, smaller than any of those so far
mentioned, which is sometimes called the "lesser house fly."[7] This
insect is distinguished from the ordinary house fly by its paler and
more pointed body. The male, which is commoner than the female, has
large pale patches at the base of the abdomen, which are translucent
when the fly is seen on the window pane. These little flies are not the
young of the larger flies. Flies do not grow after the wings have once
expanded and dried.
[Footnote 7: _Fannia canicularis_ L.]
[Illustration: FIG. 1.--The stable fly. Much enlarged.]
[Illustration: FIG. 2.--One of the green-bottle flies (_Lucilia
caesar_). Much enlarged.]
In late summer and autumn many specimens of a small fruit fly, known as
the "vinegar fly,"[8] make their appearance, attracted by the odor of
overripe fruit.
All of these species, however, are greatly dwarfed in numbers by the
common house fly. In 1900 the senior author made collections of the
flies in dining rooms in different parts of the country, and found that
the true house fly made up 98.8 per cent of the whole number captured.
The remainder comprised various species, including those mentioned
above.
[Footnote 8: _Drosophila ampelophila_ Loew.]
[Illustration: Fig. 3.--The true house fly. Enlarged.]