How long long do they live ?This is a complicated question because it has two season's of life here is a calendar view
February to March : Monarchs hibernate here in Southern California and Mexico and February and March is when they wake up, and start the search for there new mate. Once they Mate then they take flight north to lay their eggs. Then their life cycle is complete. They have lasted through the Winter just to do this for us.
March and April : The first Monarch's are born and start the life cycle through the rest of the months. It repeat;s the same cycle from May/June to July/August then in
September and October : The last (4th) generation is born from egg to caterpillar to chrysalis then butterfly. The difference with the 4th generation is these have a longer life cycle. It Migrates south and lives 6 to 8 months in Mexico or here in Southern California. Then the whole cycle begins again in February and March of the following Spring when they lay their eggs.
Here are some pictures for you to look at it is quite interesting.