
AQUATIC INSECTS OF FRESHWATER 

Dracon-F ies belong to the order of Odonata, signifying a tooth. 
More than 2000 species have been established, of which about 300 inhabit 
the United States. They are very slender insects having four elongated 
membranous wings, finely 
netted with veins, each with 
a jointed structure or nodus 
near the muddle of the: - pre! 254 \\tarva of a 
front margin. The head is ae te 
large and may be rotated mask, Enlarged. 
on the slender neck, and the 
large eyes are placed at the 
sides of the head. The an- 
tenne are short and slender, 
the mouth parts developed 
for biting and the legs placed 
near the front of the thorax 
and fitted more for grasp- 
ing their prey and adhering 
to leaves and twigs than for 

walking. ‘They are day 
, FIG, 215. Nymph of a Dragon-fly, 
flyers, the prey being cap- Anax junius, with mask folded, not visible 
from above. © Enlarged. 
tured by the legs and man- 
dables in their darting flights. It consists of flies, mosquitoes, midges, 
gnats and other small insects. All the species are aquatic. ‘The eggs are 
laid in the water, on the stems or in the tissue of aquatic plants. As soon 
as the young are hatched they begin their predatory life under water, feed- 
ing upon eggs, larve, small insects and entomostraca, which is continued 
during their entire larval and nymphal existence, attacks being directed 
to larger insects and animals as they increase in size. The larve and 
nymphe, Figs. 214 and 215, have a formidable structure known as a 
mask, consisting of a long, hinged apparatus with sharp hook teeth which 
may be folded under the head or darted forward to seize insects and 
fishes to draw them to the mouth. Most of them breathe by rectal gills, 
this apparatus also affording the means of locomotion by the violent ex- 
pulsion of the water. Some have both lateral and caudal abdominal gills. 
There is a marked difference in appearance between the larva and 
nymph of most species, the latter assuming a broad, flat form different 
from the slender larva and the adult insect. Both larva and nymph have 
short wing pads. When the final metamorphosis takes place the nymph 
crawls out of the water, the skin splits over the back, and the adult 
dragon-fly emerges. From nine to twelve months are required to develop 
261 
