ORTHOPTERA. 
171 
Stone-Flies. 
its appearance. The emergence of May-flies takes place at different periods during 
summer and autumn, and that of any one species may last for several days in 
succession. At this time they sometimes appear in countless numbers, as thick 
in the air as snowflakes, and at the end of their brief existence leave their dead 
bodies to cover the ground, or float in masses down the stream. 
Nearly fifty species of Ephemeridce are found in the British Islands. Two of 
the commonest (Ephemera vulgata and E. clanica ) are, in the subimago stage, 
known to anglers as “green drake,” and “grey drake.” They are four-winged 
species, with a body from one-half to three-quarters of an inch in length, and 
furnished at the end with three very long tails. The fore-legs are extremely long, 
especially in the males, which sex is distinguished also by the much larger size of 
its eyes. The larvae of E. vulgata burrow in the mud, or hide under stones, in 
ponds and sluggish streams. They have rather long antennae, and the tusks of 
their mandibles project a good way, and cross one another in front of the head. 
They have six pairs of tracheal gills, which are turned up over the back, each gill 
consisting of two narrow blades, united at the base, and fringed with hairs along 
each side. The final transformations of the larvae occur about the end of May, or 
early in June, at which time, on a fine evening, the winged insects may sometimes 
be seen in hundreds, dancing in the air. 
The stone-flies ( Perlidce ), forming the last group of Pseudoneur- 
optera with aquatic larvae, are narrow, elongated insects of a flattened 
form, with a good-sized head, rather 
long, many-jointed antennae, and four 
not very closely reticulated wings, 
which shut horizontally over the body 
when at rest. The abdomen usually 
carries two long, multiarticulated 
styles at the extremity. The mouth- 
organs are weakly developed in the 
adult insects; the mandibles and 
maxillae are membranous; the maxil¬ 
lary palpi long, with slender terminal 
joints, and the labial palpi three- 
jointed. The thorax is square or 
oblong, with its three segments 
almost equally developed. The tarsi 
are three-jointed, and have their claws 
separated by a bilobed pad. The 
species of this family are not numer¬ 
ous, though some are almost worldwide in their distribution. The adults appear 
about the same time as dragon-flies and alder-flies, and frequent nearly the same 
places. Though they have large enough wings, they fly heavily, and not for any 
considerable distance at a stretch, and are generally most active in the evening. 
The female fastens her eggs loosely together, and drops them in masses as she flies 
over water. The larvae are mostly found in rapid streams, where they keep under 
stones, or among broken pieces of wood, and live by preying actively upon the 
common stone-fly (Perla bicaudata). 
1, Larva ; 2, The fly escaping from the larval skin ; 3, The 
perfect insect. 
