Invertebrates of the Rideau River: Meet dragonfly and damselfly nymphs.
|Damselfly nymph of the genus Enallagma.
Notice the three long leaf-shaped gills at the hind end of its body.
Class: Insecta - Insects
Order: Odonata - Odonates (Dragonflies and damselflies)
Family: Libellulidae - Common skimmers
Characteristics of the family:
Nymphs are crawlers that move about slowly in dense vegetation and bottom
debris. They are usually long-legged and dull in colour.
Dragonflies are divided into two main groups:
dragonflies (Anisoptera) and damselflies (Zygoptera).
Adult damselflies usually rest with their
wings folded upwards, whereas dragonflies hold their wings horizontally
outwards. Damselfly nymphs have three external
at the end of the body, whereas dragonfly nymphs do not. Damselfly adults
and nymphs are smaller and more slender than dragonfly adults and nymphs.
|Dragonfly nymph of the genus Erythemis.
||Nymphs are short and broad
with long legs. Unlike many in this family, animals in this
genus lack dorsal hooks on the abdomen. Because they are such
slow-moving, sedentary animals, they are often fouled, or coated
with a layer of algae or sand that persists until the animal
||Widely distributed in North
||Slow-moving water habitats
including temporary and permanent ponds, ditches, marshes, swamps
and lake shoreline. They crawl along the bottom among vegetation
||Feed on crustaceans, molluscs,
insects or some worms and leeches. These nymphs use a specialized
lower lip to seize prey; the lip rapidly unfolds to extend and
refolds to contract. The length of the lip is approximately
equal to 20 to 25% of the length of the body. This lower lip
holds prey at the mouth while the jaw-like mandibles crush the
||Eggs are laid on sand or silt
close to the water surface. After having carried the female
around for up to a week prior to mating (thus males assure themselves
a female to mate with when she is ready), the male continues
to grasp the female as she lays her eggs in order to protect
her from other males. Eggs hatch after one to several weeks
or a long diapause
(overwintering). Nymphs undergo 11 to 12 stages of development
during their development. Once this is complete, they crawl
from the water onto emergent vegetation or onto the bank. Life
cycle is usually one year.