LIBRARY

214
COLLEGE ENTOMOLOGY
the skin. With the first molt the gills arise, a pair at a time in successive molts.
The young or naiads normally hide on the bottoms of streams and lakes under
stones, debris, and aquatic vegetation. Occasionally they may be seen darting
across open spaces or clinging to stones and other supports. The thin flat spe­
FIG. 77. Eggs of mayflies. A, TTicorythodes
ollectu$ (Needham); B, Isonychia albomanicata
(Needham); C, Stenonema interpunclata (Say);
D, EphemeTella rotunda Morgan; E, Ephoron
album (Say). (All after Morgan, 1913.)
E
cies cling tightly to rocks where the
current is swift, and other forms are
found in quiet. waters where they
move freely among the water flora.
The naiads of still other species are
fossorial and burrow in the mud on
the bottoms or in the banks of
streams. They are capable of very
rapid movement in water, swimming
by means of the fringed caudal appendages
and the gills.
According to Morgan (1913),
"Mayflies are almost entirely herbivorous.
Their food consists chiefly
of fragments of higher plant tissue,
algre and diatoms." Nymphs of
two species are reported injurious to
structural timbers below water in
Thailand (Rev. Appld. Ent. Ser. A, 26:
149, 1938). Certain amounts of ani.
mal food in the form of other mayfly
naiads and aquatic insects are eaten
by some species. The young of some
species are very interesting aquarium
animals that furnish ample opportunity
for many delightful observations,
providing they are supplied
with the necessary plant. life, aeration,
and the exclusion of predators.
The complete life history of the
naiads is rather difficult to study
and that of but few species is accurately
known. Naiadal development
is usually rather slow, requiring from
1 to 3 years. During this period the
naiad may undergo as many as 24 molts. However, in certain species de"
velopment is rapid. The life cycle of CalUbcetis is completed, according to
Needham and Lloyd (1930), in less than 6 weeks. If a single female lays 1,000
eggs and all develop and reproduce through a single season the members of
the fourth brood would number 125 billions. Of course such a phenomenal increase
is not possible, but these figures give some idea of the reproductive