pair, when present, is small and rounded. The antennae are bristlelike and in- 
conspicuous; the mouth parts, vestigial. The nymphs are elongate and cylindrical or 
flattened, and have leaflike gills along the sides of the body. In most species the 
gills have three long tails. 
Mayfly nymphs live under stones or among debris on the bottom of streams 
where they feed on decaying vegetable matter, algae, and diatoms. When they 
become full grown they leave the water and transform to adults on nearby vegeta- 
tion. The adults occasionally appear in enormous numbers, but they seldom live 
longer than a day to two. Occasionally, their dead bodies literally pile up along the 
shore, on bridges, or in the streets of nearby towns (9//). 
Beyond the occasional nuisance created by the presence of piles of dead insects in 
areas frequented by humans, and the importance of the nymphs as fish food, which 
is substantial, mayflies are of no economic importance. 
Order Odonata—Dragonflies and Damselflies 
Dragonflies and damselflies are relatively large and often beautifully colored 
insects. The adults have two pairs of elongate, membranous, many-veined wings of 
about equal size. The head and the compound eyes are large, the antennae are very 
small and bristlelike, and the abdomen is long and slender. Dragonflies may be up 
to 75 mm long and they hold their wings in a horizontal position while at rest. 
Damselflies are usually somewhat smaller. Their wings are folded along the 
abodomen or are tilted up while at rest. Adults of both groups feed on various 
insects they capture while in flight. They are common and often abundant around 
slow streams and ponds. Dragonflies are particularly noticeable because of their 
large size and their rapid flight back and forth over the water. 
Dragonfly and damselfly nymphs are all aquatic and feed on various small 
aquatic organisms. Prey is captured through the use of a modified labrum contain- 
ing two movable clawlike lobes at the tip. This device is held folded under the head 
when not in use and is about one-third as long as the body when fully extended. The 
nymphs breathe by means of gills. In the dragonflies, gills are in the rectum; in 
damselflies, gills are three leaflike structures at the end of the abdomen. Mature 
nymphs crawl out of the water and transform to the adult stage, usually on rocks or 
vegetation. 
Order Plecoptera—Stoneflies 
Stoneflies are small to medium-size drab insects with soft flattened bodies. The 
wings are membranous and have numerous cross veins. The front pair is rather 
narrow and elongate; the hind pair is shorter but wider and is usually folded in 
pleats while at rest. The antennae are long, slender, tapering, and many-segmented. 
The cerci, when present, are usually long and many-jointed. The nymphs are flat- 
bodied and somewhat elongate. They have long antennae, long cerci, and branched 
gills on the thorax and about the base of the legs. 
Stonefly adults occur near streams or along rocky shores of lakes. The nymphs 
are aquatic and are usually found under stones in rapids of streams. When they 
reach maturity, they leave the water and climb up on nearby objects to transform to 
the adult stage (909). 
Stoneflies may be a nuisance at times, especially when they appear in swarms in 
recreational areas. The nymphs are an important source of fish food. 
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