Science of Water : Concepts and Applications

Water Ecology 197
FIGURE 6.32 Damselfl y.
leaving them to hatch or by inserting eggs singly into a slit in the stem of a submerged plant. The
incomplete metamorphosis (egg, nymph, mature nymph, and adult) can take 2–3 years. Nymphs are
often covered by algal growth.
√ Note: Adult dragonfl ies are sometimes called “mosquito hawks” because they eat such a large
number of mosquitoes that they catch while they are fl ying.
Damselfl ies are smaller and more slender than dragonfl ies. They have three long, oar-shaped
feathery tails, which are actually gills, and long slender legs (see Figure 6.32). They are gray, greenish,
or brown to black in color. Their habits are similar to those of dragonfl y nymphs, and they emerge
from the water as adults in the same manner. The adult damselfl ies are slow and seem uncertain
in fl ight. Wings are commonly black or clear, and their bodies are often brilliantly colored. When
at rest, they perch on vegetation with their wings closed upright. Damselfl ies mature in 1–4 years.
Adults live for a few weeks or months. Unlike the dragonfl ies, adult damselfl ies rest with their wings
held vertically over their backs. They are predaceous and mostly feed on live insect larvae.
√ Note: Relatives of the dragonfl ies and damselfl ies are some of the most ancient of the fl ying
insects. Fossils have been found of giant dragonfl ies with wingspans up to 720 mm that lived
long before the dinosaurs!
NONINSECT MACROINVERTEBRATES
√ Note: Noninsect macroinvertebrates are important to any discussion of stream and freshwater
ecology because many of them are used as bioindicators of stream quality.
Three frequently encountered groups in running water systems are Oligochaeta (worms),
Hirudinea (leeches), and Gastropoda (lung-breathing snails). They are by no means restricted to
running water conditions and the great majority of them occupy slow-fl owing marginal habitats
where the sedimentation of fi ne organic materials takes place.
(1) OLIGOCHAETA (FAMILY TUIFICIDAE, GENUS Tubifex)
Tubifex worms (commonly known as sludge worms) are unique because of the fact that they build
tubes. Sometimes there are as many as 8000 individuals/m 2 . They attach themselves within the tube
and wave their posterior end in the water to circulate the water and make more oxygen available