The Stream Doctor

November 4th, 2002

Your questions and answers about everything stream related.

Q. From Matt in Rose City, Michigan: What is the difference between a larva and a nymph?

A. Quite a bit, although we pretty much blur the distinction in fly-fishing jargon when we use the general term "nymph fishing' to describe using imitations of both larvae and nymphs. Immature forms of insects such a mayflies and stoneflies are true nymphs. They differ from those insects having larvae in that successive stages of the immature nymphs (called instars) are similar in appearance, except for the wings, to the adults and, most importantly, they do not go through a pupal stage. For caddisflies and dipterans, the various larval instars do not resemble the adult forms, e.g., an adult chironomid has no resemblence to the larval, worm-like forms. These insects progress from an egg to a larva and then enter a pupal state where the transformation from immature to adult form takes place. Technically, insects with nymphal forms are called hemimetabolous, while those going through a pupal state are called holometabolus. ~ Stream Doctor

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to stream-ecology directly to him for use in this Q & A Feature at

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