Monarch Butterfly, Danaus plexippus

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Monarch Butterfly, Danaus plexippus

Diet of the Monarch Butterfly Larva

The Monarch butterfly larva feeds on milkweeds. Some of their favorites are the Monarch Milkweed, Asclepias eriocarpa and the Narrow leaf milkweed, Asclepias fascicularis. Milkweeds contain toxins that make the adult poisonous to birds and other predators. Most insects can eat the monarch without effect. They are preyed upon by Stink bugs and Assassin bugs.

There are many kinds of milkweeds. We usually have three species in stock. They are easy to grow and look nice in a garden. Some of the reasons Monarch's are having problems is the removal of native Milkweed species and the introduction of other milkweed species into gardens.

The Monarch and Migration

The Monarch butterfly is an amazing insect because it migrates. This is an incredible feat as it is sensitive to temperatures, easily blown around by the wind, and has to travel nearly two thousand miles to a place it has never been. It also has a very rudimentary nervous system compared to the vertebrates, like birds, that migrate. When temperatures begin to drop in the US and Canada, these insects begin to head south to their overwintering areas in Mexico and California. When temperatures begin to rise again, the insects move north. Many butterflies are tagged (photo above) by researchers who are trying to learn more about their migration.
Monarch butterfly milkweed. Notice the two caterpillars of Monarch Butterfly, Danaus plexippus,  butterfly - grid24_12
There are two monarch butterfly larvae on this Monarch Milkweed, Asclepias eriocarpa. (Look on the underside of leaves. One is near the top and one is close to the bottom.)

The Diet of the Adult Monarch Butterfly

The Monarch butterfly feeds on nectar form various flowers including milkweeds, Asclepias sp. In the picture below a monarch butterfly feeds on an Asclepias speciosa. This is a large milkweed that does very good in gardens. It has large showy flowers and large leaves.

They also like Butterfly mint, Monardella spp, below a monarch butterfly is sipping off an annual species. However, there are many perennial species that are very good in gardens. One of the most attractive ones is Monardella antonina, Butterfly Mint Bush, this species is very popular with butterflies.

Some other flowers that are used by the Monarch butterfly are; Salvia mellifera (Black Sage), Trichostema lanatum (Woolly Blue Curls), Agastache urticifolia (California Licorice Mint), Chilopsis linearis (Desert Willow), Helianthus gracilentus (Dwarf Sunflower), Encelia californica, Mahonia nevinii (a species related closely to Oregon Grape), Ribes aureum var. gracillimum (Golden Currant), Dichelostemma capitatum (Wild Hyacinth), Isomeris arborea (Bladder Pod), Lobelia dunnii (Blue Lobelia)and Cirsium occidentale var. venustum (Venus Thistle)

A short video about Asclepias eriocarpa Monarch Milkweed and Indian Milkweed.

The alkaloids associated with native milkweeds give the butterflies that feed on it protection. Alkaloids from the wrong milkweed(South American, Mexican, etc.) can expose the butterflies to predation. If the monarch or other butterfly has not evolved with the milkweed they have no tolerance for the particular alkaloid of the species. The California flyway runs from Baja to Canada, it does not include Mexico proper nor Central America. If you live in Chicago you can plant Mexican species (Asclepias mexicana) or Asclepias tuberosa, don't plant our species. I would guess the symptoms to be similar to the problem of intolerance to legumes that some people have. Moreover the exotic species have a different parasite load and can harbor much higher numbers of parasitic spores. ( DeRoode, JC and Altizer, S. 2010. Host-parasite genetic interactions and virulence-transmission relationships in natural populations of monarch butterflies. Evolution, 64:502-514.:De Roode, J.C., Yates, A.J. and Altizer, S. 2008. Virulence-transmission trade-offs and population divergence in virulence in a naturally-occurring butterfly parasite. PNAS. 105: 7489-7494.) Moreover, butterflies that do not migrate commonly decline because of parasitism. Feeding Southern California Butterflies Milkweeds all year is not a good idea. (Altizer, S., Han, B and Bartel, R. 2011. Animal migrations and infectious disease risk. Science. 331: 296-302)