monarchs and swan plants

Paul Cherubini paul at
Wed Jan 20 21:28:42 EST 1904

> On May 9 Sunsol Daniels wrote:

> > I'm in Berkeley.  Is it wishful thinking that I am on the "central
> > Calfornia coast?"  What time of year do the Monarchs lay?  The swan plant
> > around here is looking pretty ratty now.  Maybe it needs to be cut back
> > in the winter so it has fresh foliage for the spring and summer...

I grew up in nearby Castro Valley and monitored monarch breeding at wild patches of 
Asclepias fascicularis growing along railroad tracks and roadsides in Hayward and 
Fremont for many years in the late 1960's and 70's. Egg laying females, patrolling males 
and/or monarch caterpillars could be found in a majority of years almost any time between 
late March and November. These reproductive adults were typically fairly common in late 
March/early April, rare in late April & May, occassional in June & July, then fairly 
common by August and September when the milkweed was blooming. Large, permanent 
monarch overwintering sites (with ~10,000-55,000 butterflies for the past three 
consecutive years) exist in this same highly urbanized area: at the San Leandro Marina 
Golf Course in San Leandro, at the Sky West Golf Course in Hayward and the 
Ardenwood State Historic Farm in Fremont. Curiously, back in the late  60's, & 70's  
when the area was less developed, the only large permanent site in the East Bay was at 
Ardenwood and numbers back then were closer to 5,000 instead of the 10,000-25,000 
we have seen there for the past three years in a row. The big daddy site in the East Bay is 
in the eucalyptus trees at the Sky West Golf Course in Hayward with 55,000 monarchs 
there in the winter of 1997-98 and 20-25,000 last winter. This "site" was just a treeless 
wheat field in the 1960's thus demonstrating new monarch overwintering sites can be 
easily be constructed from scratch--on bare land that has no history of supporting 

This spring, statewide populations of monarchs are a bit lower than normal so it is 
unlikely you'll see monarchs in Berkeley until the regional population rebounds by July 
or August. Monarchs are more common in summer a little further east such as in Walnut 
Creek and on Mount Diablo.  For example,there are scattered patches of Asclepias 
fascicularis growing along the main road that goes to the summit of Mount Diablo. In late 
July and August when this milkweed is in bloom, monarchs and caterpillars are quite 
common in a normal or high monarch population year.  

Paul Cherubini, Placerville, California

More information about the Leps-l mailing list