INSECTS. 
ft 
MALE OF COMMON MAY - FLY, 
Ephemera vulgata (nat. size). 
weather, however, they may sometimes be seen assembled together in swarms 
about sundown, and engaged in their pastimes, which are continued till some time 
after sunset. The peculiar up-and-down movement, which marks the flight of 
some species, has been often observed; and the mazy dance of the Mav-flies has 
v been described by more than one author. In these 
dancing assemblies the male insects always greatly 
outnumber those of the other sex. The larvae of 
the Ephemeridce live in water; a few kinds are 
carnivorous, but most feed upon the minute vegeta¬ 
tion scattered through the mud or covering stones, 
and the larger aquatic plants. Many remain con¬ 
cealed in the banks or under stones, while others 
rove among water-weeds, and swim with celerity. 
The larvae of some genera are found only in large 
rivers. The eggs are, in some cases, deposited at the 
surface of the water, and then sink to the bottom; 
but in others the female creeps into the water to 
lay her eggs in patches on the under side of stones. 
The eggs are exceedingly numerous, and vary in 
shape according to the genus. The larvae cast their 
skin several times; they are at first without special 
organs of respiration, but when they are about eight or ten days old tracheal gills 
begin to appear and ultimately develop into forms, which vary somewhat in the 
different genera. The gills axe attached in pairs to the sides of some, or all, of the 
first seven segments of the abdomen, in 
some species standing out straight from 
the sides, and in others turned over the 
back. The mouth-organs of the larvae are 
better developed than in the adult, the 
mandibles being nearly always strong and 
toothed, and sometimes giving off a tusk¬ 
like process in front of the head. At their 
transformation most May - flies do not 
change directly from the larval form into 
the imago, but first pass through a stage, 
known as the subimago, in which they 
have their wings expanded, and breathe 
through the spiracles like the perfect 
insect. In this form they are distin¬ 
guished by the dulness of their integu¬ 
ment, the shortness of the fore-legs and 
tail-bristles, and the less prominent and 
duller eyes. The subimago emerges from 
the larval skin at the surface of the 
water, and, after standing awhile upon the water, flies to a more convenient 
resting-place. At the next moult, which soon follows, the perfect insect makes 
A MAY-FLY AT ITS FINAL MOULT, WITH THE IMAGO 
ESCAPING FROM THE SKIN OF THE SUBIMAGO. 
THE LARVA BELOW. 
