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Aquatic Invertebrates


From Egg to Insect

The series of transformations from egg to adult undergone by an insect is called metamorphosis. This process is called "complete" when certain major changes take place during the course of development. It is called "incomplete" when there is little difference between the young insect and the adult.

Synclita sp.
This aquatic caterpillar (of the genus Synclita) will one day become a moth.
Complete Metamorphosis
Stages: egg, larva, pupa or chrysalis, adult
In insects that undergo a complete metamorphosis, the larva and the adult are usually so different that it can be difficult to tell that they belong to the same species. The larvae are called different names, according to their insect group: larva of a butterfly is called a caterpillar, that of the fly is called a maggot, and that of a beetle is called a white grub.

Development consists of a series of moults, an increase in size and, sometimes, changes in colour. The final moult produces a pupa (also called a chrysalis) that is usually dormant and does not feed. The adult insect will emerge from this stage.

Among the insects that undergo a complete metamorphosis are moths, caddisflies, beetles, flies, gnats and mosquitoes.

It may take them as little as a few hours or as much as several years, depending on species, habitat, temperature, etcetera.

Incomplete Metamorphosis
Stages: egg, nymph, adult
In insects that experience incomplete metamorphosis, an animal in the larval stage is called a nymph and differs from the adult mainly in size and the proportions of the body. The metamorphosis of the true bug is an example of this type of development.

The mayfly, dragonfly and damselfly are exceptional in this category: the nymphs resemble the adults, but there are also some differences. Among other reasons, these differences are related to the fact that the nymph lives in water while the adult lives out of water.

Several nymphs of different insect species were observed in the Rideau River during the course of the Rideau River Biodiversity Project.

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Damselfly nymph of the genus Enallagma.

Insects Rule!
Did you know that insects are the most successful animals that have ever existed on Earth? They are found almost everywhere, including, of course, the Rideau River. Dragonflies, damselflies and mayflies are among the many aquatic insects that live in water only as juveniles. This damselfly nymph (of the genus Enallagma) is an example.


A Project of the Canadian Museum of Nature
 Images: Chris Allaway, Ed Hendrycks, Valerie J. May