Monday, July 14, 2014

Monarch Butterflies

The spring Monarch Butterfly migration passed without a single Monarch sighting at Blue Jay Barrens.  My earlier disappointment has been abated with a summer season Monarch count surpassing any in recent years.  The Milkweed stands are receiving frequent visitations from this colorful butterfly.

Of course, this is the real reason for maintaining patches of Milkweed plants.  Monarch larvae are Milkweed eaters.  Recent declines in the Monarch population make it more important than ever that this plant be readily available.

Having Milkweed plants snug up against the house makes it easy to monitor the progress of leaf eating insect larvae.  Because of a beating they took during a spring thunderstorm, a few of the plants are unable to maintain an upright position.  Most, however, are standing tall, even though a few needed some propping up and stem support to achieve this condition.

Landscape designers probably wouldn’t recommend crowding the entrance to your home with seven foot tall Milkweed plants.  I would agree, especially when the flower visiting bees during the day or moths at night get sucked into your home every time you open the door.  This Milkweed thicket was not actually intentional.  A single plant that became established beside the water garden was allowed to remain.  Within a couple of years that one plant became two dozen.  For the benefit of the Monarchs, I let them remain.  I must admit that I am also fascinated by the vast array of insects attracted by these plants.

I’m currently finding larvae of all ages.  The youngest are just beginning to show their characteristic black filaments.  Small larvae are easiest to see by looking from below a sunlit leaf. 

Midsized larvae show short stubs where the long black filaments will eventually be.  Larvae can also be located by examining holes in the leaves.  Feeding sites are more regular in appearance than hail damage left by the early storm.

Leaf damage causes the Milkweed plant to ooze its thick white sap.  The sticky sap can make it difficult for the larva to feed.  The larva overcomes this obstacle by systematically severing the veins leading to the leaf, this stopping the flow of sap.

In small leaves, the midrib is often cut to halt sap flow to the entire leaf.  On larger leaves, a series of lateral veins might be cut as seen here.

Once the sap stops flowing, eating commences.

The larvae seem to practice an eat-and-run technique that minimizes time spent in any one location.  A section of leaf is consumed and then the larva moves on to another location.  Many predators are attracted to leaf damage in search of prey.  Despite the Monarch’s unpalatability due to accumulating toxins from the Milkweed plant, some predators have to learn the lesson first hand to the detriment of the larva.  Even though they are bad to eat, the best survival strategy is to avoid the predators.

The excess rainfall experienced this spring has really benefited the Milkweeds in the field.  The plants bloomed early and are continuing to produce new flower buds.

This large stand of Purple Milkweed continues to attract Monarch Butterflies as well as other insects dependent on the Milkweed plant for their survival.

It appears that Blue Jay Barrens will contribute a large number of Monarchs to the masses that will make their way south later this summer.  I just hope that conditions at their wintering grounds are favorable for the species continued survival.


  1. For some reason, only a few of the photos are visible even after refreshing the page.

  2. Steve,
    Fabulous post as always. I especially enjoyed the photos of the "nipped" milkweed veins. Very nice.
    would you care to comment on the monarchs' preference of milkweed? I note you have both Common and Swamp Milkweed. It has been said they have differing amounts of the cardiac glycosides that monarchs utilize.
    Thanks for any observations you can share. Cheryl

  3. Hi, Victorian Barbarian. The problem is either internet or blogger related. I've personally been having serious problems with my internet connection and had major complications uploading this post. Once the post is uploaded into blogger however, my problems are no longer an issue with blog visitors. Hope you have better luck on your next try.

    Thanks, Cheryl. I have very few Swamp Milkweed plants and have yet to see any of those being used by Monarchs. The Swamp Milkweed is growing in small openings that generally have less Monarch visitation. The Common and Purple Milkweeds grow in the larger open fields and seem to attract Monarchs at about the same rate.