The second tribe of the _Pseudo-neuroptera_ contains a group of insects
which are so similar to one another in form that they are all included
in one family.
_Family 3, Ephemeridæ._--The _Ephemeridæ_, or Day Flies, as they are
popularly called, are delicate, elongated, soft-bodied creatures, with
a moderately small head. The antennæ, which spring from the forehead
below the ocelli, are short and awl-shaped. These insects, which seem
to be found mostly in temperate climates, are remarkable for the great
delicacy of their structure, and for the extreme shortness of their
lives in the perfect state, which seems in general scarcely to exceed a
day.
Nearly fifty species of _Ephemeridæ_ occur in this country. The
best known is _Ephemera vulgata_, of which the sub-imago is called
the "green drake," and the imago the "grey drake" by anglers. The
two-winged _Clöen diptera_, which, however, is a much smaller species
than the foregoing, is also very abundant.
[Illustration: Fig. 56.--Calopteryx Virgo (Female).]