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                                                Monarchs in the South Bay

Did you know that several small sites exist locally where Western Monarch butterflies overwinter?  Two of these “roosts” occupy branches in protective Eucalyptus trees located along the Greenbelt in Manhattan Beach and Hermosa Beach. Long-time locals have noted the annual hibernating congregations in these locations, in varying numbers, for over fifty years. 


                                                   Monarchs and Milkweed

Western Monarchs leave their overwintering sites each spring in search of a mate and milkweed to lay eggs on.  The  lucky ones will find local native milkweed varieties including Narrowleaf milkweed, Asclepias fascicularis.  This lovely drought tolerant species, favored for its nectar by Monarch adults and leaves by their caterpillars, has historically been the most common milkweed species throughout California.  It's the easiest to grow and can be found in plant or seed form at local nurseries or online retailers. 


Native milkweeds are deciduous, dying back to the ground in winter.  Their absence signals Monarchs to migrate. 

Non-native milkweed varieties are evergreen, and their availability compels monarchs to breed instead of migrate. 


Scientists have discovered greater spore loads of a protozoan parasite called Ophryocystis elektroscirrha, OE, on monarchs who do not migrate.  OE is a monarch-dependent organism spread to milkweed leaves by adults carrying the spores. It can debilitate caterpillars that consume heavily spore-laden leaves. 


Although OE has co-evolved with monarchs, according to the Xerces Society, the introduction and popularity of evergreen milkweeds, leading to fewer migrating Western monarchs, may be one factor in the butterfly’s declining numbers. 


                                                 Promote Monarch Health

Here is what government and citizens in the South Bay can do to support the health and sustainability of our local monarch populations: 


  1. PROTECT OVERWINTERING SITES from pesticides, herbicides, and inappropriate tree trimming

  2. PLANT LOCALLY NATIVE MILKWEED (pink or maroon flowers) in home and City landscapes that are 1 mile or more from the coast. Contact a local nursery or check out the “Milkweed Finder” page on for plants and seeds. Generally, these Aspecies are best for Los Angeles: eriocarpa, california, fascicularis and vestita.

  3. REPLACE NON-NATIVE MILKWEED (yellow or red flowers) or cut it way back and ensure there are no leaves throughout winter. 

  4. PROVIDE AN ASSORTMENT OF NECTAR PLANTS in addition to native milkweed such as yarrow, sunflowers, seaside daisy, black and other native sages, verbena and manzanita.  Their flowers can be accessed by monarch butterflies for nectar throughout the year. 


LEARN MORE ABOUT MONARCHS from the Xerces Society heremonarchs 


Monarch Butterfly (male)


Monarch Butterfly (female)


The photos on the left below are non-native milkweed. Do not plant milkweed with yellow, red, or orange flowers.

The photos on the right are a native variety called Narrow-leaf Milkweed, Asclepias fascicularis. The flowers are pink. Plant this if you live in Southern California!

Non-native Milkweed

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Native Milkweed

on non-native milkweed

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