26 April 2012

Monarch fecundity

These are the only such data that I am aware of collected from observation of a single butterfly in a controlled environment.  

From Journey North, where the maps show that monarchs have been sighted at our latitude.  The milkweed in our garden is waiting for them.


  1. Can you please explain what this graph is supposed to tell us? All I see is lots of eggs at the beginning, and then they peter out before it dies. What does that have to do with overcoming predation, or habitat loss? I don't know a tonne about butterflies, but monarchs come all the up to my neck of the woods, so I'd like to understand them better. (I'm in Manitoba, Canada)

    1. This graph shows that this particular Monarch butterfly laid about 750 eggs. That may or may not be typical for the species. One of those eggs has to mature and reproduce for the population of the species to persist.

      To my mind it shows that 99.8% of the eggs laid can succumb to predation (by ants and birds etc) and the species will still be successful in surviving.

      But the modern problem is that monarch populations are at risk because the one plant they need to survive (milkweed) is at risk from weed control measures by farmers. Even the historic survival rates may not be adequate if there is no place for her to lay her eggs.

    2. p.s. - the Monarch butterflies you see in Manitoba each summer fly all the way to Mexico to spend the winter. Their children return to Manitoba. How they manage to accomplish that feat of navigation, nobody knows.

    3. Stan:

      I may be wrong about this, but don't the Monarchs seen in Manitoba (as well as both Minnesota and Wisconsin) fly all the way to Mexico, and it's their GRANDCHILDREN who finally return back to Manitoba, Minnesota, and Wisconsin? I've heard that another generation is born somewhere around Texas, but could be wrong.

    4. You're quite right. The northern batch fly to the mountains in Mexico to overwinter. In the spring they emerge and mate in the southern U.S.. It is their offspring that fly north.

      Once that new batch has arrived north, they also mate and reproduce, and it is THEIR offspring that return to the same location in Mexico.

    5. Thank you for explaining! I thought the graph itself was meant to show something about milkweed loss, but it's unrelated :) I think the Monarch migration is magical (miraculous, mysterious, marvelous - it drives me to alliteration! lol)


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