LIBRARY

PLECOPTERA 149
All forms are cryptically colored to match their surroundings. The colors are
for the most part somber, being various shades of black, gray, brown, dull red,
yellow, and pale green. Members of the Tasmanian genus Eusthenia have
beautiful red hind wings bordered with purple. Eustheniopsis venosa Tillyard of
Australia has purple hind wings, while the large black Thaumatoperla robusta
Tillyard of the same continent has a bright-orange pronotum. They are slow
and erratic fliers and seldom wander far from their breeding places. Rather
they are to be found resting upon stones, logs, grasses, shrubs, and trees along
the margins of streams, lakes, and ponds and are often exceedingly numerous
in certain hilly and mountainous regions where swift running water and rocky
bottoms are available. The eggs are laid directly in the water and in some cases
are extruded in a sac which is carried by the female before final deposition.
They are frequently very small and are laid in astonishing numbers of 5,000 to
6,000 per single individual. The nymphs or naiads live under debris in eddies or
under stones in clear, well-aerated fresh water. Although apterous, they look
remarkably like the adults. Tracheal gills in the form of tufts or paired lateral
filaments occur on the first five or six abdominal segments or are arranged as a
rosette around the anus, or they may be entirely lacking in which case respiration
occurs through the rectum. After a number of molts the wing-sheaths develop,
and with the final metamorphosis the naiads leave the water and cling to
stones, logs, roots, and shrubbery along the waterways and the adults emerge
through a longitudinal slit in the dorsum of the thoracic region, leaving the
empty skins as mute evidence of their having forsaken the water for a life of
aerial freedom. The immature forms feed largely upon the larVa:! of mayflies,
midges, and other small aquatic animals, but some at least are thought to
feed upon the vegetable debris that collects along the bottom. The larger forms
are formidable predators, and, though most nymphs are slow, some are remarkably
agile. All stages are in turn consumed by fish and form a considerable
part of the diet of trout and other game fish. The adults often issue during
the fall, winter, and early spring when it is necessary to leave the water through
cracks and crevices of the ice. According to Frison (1929), "At least ten species
of stoneffies in Illinois respond to cold weather in this way. To anyone not well
acquainted with our fall and winter fauna, it is a startling revelation to see such
large insects sprightly climbing up tree trunks in search of food when temperatures
are near or below freezing, or to watch them crawling over the ice and
snow which partly holds in its embrace the waters that nurtured their infancy."
The adults appear to feed but little. Certain species are herbivorous and
feed upon the leaves of plants growing within their scope of activities.
External Anatomy. - The most important features of the external anatomy
are already enumerated and are shown in the accompanying illustrations.
There are normally three ocelli of which the median is smallest, but there may
be only two in NeoperZa and Peltoperla, or none at all. The mouth parts of many
of the species of the northern regions are greatly reduced. In the PERLIDJE
the mandibles are normal, but in the others they are poorly developed. Representatives
in the Southern Hemisphere have strong mouth parts and are largely