Monarch Biology

There are a number of outstanding sources of information about monarch biology.

Journey North
http://www.learner.org/jnorth/monarch/index.html
Journey North engages students in a global study of wildlife migration and seasonal change. The site has a Frequently Asked Questions section with a wealth of information about monarch biology at http://www.learner.org/jnorth/search/Monarch.html

The Monarch Butterfly in North America
From the USDA Forest Service
http://www.fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/index.shtml
This web site has basic information about the monarch life cycle, migration and overwintering, and habitat needs.

Monarch Lab: Monarchs in the Classrooms
http://www.monarchlab.org
Monarch Lab has several sections with information about monarch biology including:
-- Annual Life Cycle
-- Monarch Life Cycle
-- Global Distribution
-- Ask the Expert

Monarch Watch
Monarch Watch has information on anatomy, sexing monarchs, life cycle, sensory systems, predation, and more.
http://www.monarchwatch.org/biology/index.htm

North American Monarch Conservation Plan
http://www.cec.org/islandora/en/item/2350-north-american-monarch-conservation-plan-en.pdf
The North American Monarch Conservation Plan has an excellent fact sheet and description of the species.