The monarch butterfly (Danaus plexippus) is a robust species that has one of the longest migration patterns in the insect world. Literally hundreds of millions are known to migrate to central Mexico, Los Angeles, Ventura, Orange County and Santa Barbara from all over the country and Canada each year to roost for the winter months, but these numbers are dropping at an alarming rate. A recent CBS News report reflects that the monarchs covered 1.65 acres of the pine and fir forests west of Mexico City last winter. That's down from 2.93 acres last year and a decrease from a record 44.5 acres in 1996.
Monarchs need the milkweed plant to survive, as it is the only plant on which they will lay their eggs. Scientists say the use of herbicides to eradicate weeds (including milkweed) from farmlands and public roadways is one of the main reasons the monarchs are disappearing, along with illegal deforestation in Mexico and severe winter weather. Farmers are growing genetically altered crops designed to withstand the effects of herbicides, so when these crop fields are sprayed with herbicides, only the weeds are affected. The use of herbicides has increased over the years amid this process, and it appears to be killing off the monarch population.
When the monarch eggs hatch, the larvae grow into caterpillars that feed on the milkweed leaves, which contain a milky sap that makes them poisonous and unattractive to predators. After eating the leaves, the caterpillars form chrysalises, and their metamorphosis is complete when the monarchs emerge.
The milkweed I grow in my garden is Asclepias tuberosa, commonly known as butterfly weed. It is native to eastern North America. Green Gardens Nursery in Pacific Beach, at 4910 Cass St., has just begun stocking narrowleaf milkweed (Asclepias frascicularis) and showy milkweed (Asclepias speciosa), both native plants I plan to add to my garden. All milkweed is drought-tolerant and will attract monarchs. As a bonus, it will attract bees and beneficial insects to your garden.
Linda is a Realtor with Coldwell Banker. Information on her garden has been published in local and national magazines. Take an updated tour of Linda's Garden on LindaMarrone.com.