10 BUTTERFLIES AND MOTHS. 
they belong. Some pupz are found suspended, others are 
enclosed in a silken or earthen cocoon, while still others are 
found in a smooth cell in the earth. 
After remaining in this condition for a shorter or longer 
time, the imago or perfect insect leaves the pupal skin 
through an opening in the back. At first the wings are very 
minute, being folded up in numerous wrinkles; but they ex- 
pand very rapidly, and as soon as the tubes or veins in the 
wings are filled with air, and the skin covered with scales is 
fully expanded and dried, the insect can fly about, a thing of 
beauty, and a very different being from a crawling cater- 
pillar. 
More than six thousand species of lepidoptera have been 
described from North America, north of Mexico, which re- 
present more than sixty families. In order to giveasynopsis 
of the lepidoptera, it would be necessary to enter into rather 
difficult technical details, and a bulletin like this is not the 
proper place to do so, hence those that wish to study this 
order more in detail are referred to such valuable works as 
those published by Comstock, Packard, Smith and others. 
In a rather crude way we divide the lepidoptera into 
two groups, into Butterflies and Moths, the Rhopalocera 
and Heterocera. These terms are derived from the form of 
the antennz of these insects; Rhopalocera are those in which 
the antennze terminate in a more or less distinct knob or 
club at the tip, and in which at least the front pair of wings 
are elevated and vertical when at rest, so that the upper 
surfaces touch, as may be seen in the illustration of Grapta 
(page 68). The Heterocera possess feelers of many different 
kinds, none of which are distinctly clubbed; their wings, 
when at rest, are horizontal, folded on the back and close 
to the sides, oblique, roof-like or spread out flat, but never 
habitually vertical. Usually butterflies are active during the 
day, while moths are night-flyers; this is a rule which has, 
however, many exceptions, as some moths fly during theday. 
The Butterflies separate readily into groups based on 
the character of the feet and the situation of the antenne. 
