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National Wildlife Federation/ San Diego County
Butterfly Basics
by Diane Greening, Habitat Steward
A butterfly's life consists of four distinct stages: egg, larva (caterpillar), pupa, and adult (butterfly), each with its own requirements for life. Female butterflies will only lay their eggs on specific plants that serve as caterpillar food sources (larval food). Their sensitive scent receptors in their feet can tell the difference between related species and choose the correct one for her eggs. (Scientists found that
butterflies can sense the difference between the cannabidiol that causes
a human high and the components of hemp which do not. Was this
experiment the result of a late night scientific impulse or an attempt to
replace drug-sniffing dogs with butterflies?) Depending on the species of
butterfly, the female may lay her eggs in a clump or singly, usually on
the underside of leaves, although some butterflies deposit the eggs on
or in the ground near a larval food plant. When the eggs hatch into
caterpillars, food is immediately at hand.
Caterpillars, like the ones in Eric Carle's picture book, The Very
Hungry Caterpillar, just eat and eat and eat. Although they have a bad
reputation for this among farmers and gardeners, very few butterfly
caterpillars are agriculturally destructive. Their selective nature insures
that they will only eat one or two species, and while the amount they
consume is prodigious for their size, it is usually not enough to harm a
plant. (One of the few exceptions is the cabbage white butterfly,
introduced here from Europe in the early 20th century; its larva eats
plants in the cabbage and broccoli family.)
As the caterpillar grows it changes in appearance and sheds its skin
four or five times. As it nears the final stage the caterpillar may
leave the larval food source, seeking a safe place to pupate. Some
caterpillars attach themselves to stems using their own silk; others hide
under leaf litter or nestle in rough tree bark. The final larval stage
lacks feet and its skin hardens into the chrysalis. The pupa transforms
for about two weeks.
Finally the day comes for the butterfly to emerge from its chrysalis.
It make take hours to free itself, and then must wait another hour or
two to allow its internal fluids to fill out the wings, and for the
wings to dry. Most adults feed on nectar, although some feed on rotten
fruit, carcasses, or dung, and a few survive solely on the fat produced
when they were caterpillars. Cold-blooded butterflies must absorb enough
solar energy to allow them to fly. Butterflies that bask in the sun
with their wings open usually have light wings that reflect light onto
their dark bodies which soak up the heat. Another adult behavior is
puddling: male butterflies congregate at muddy sites to take in minerals
and salts from the soil.
San Diego: A Winter Refuge for the Migrating Monarch
Like the California Gray Whales on their way to the Gulf of California,
Monarch butterflies leave their northern homes in late summer and early
fall seeking warmer temperatures. A Monarch cannot fly at 55 degrees
Fahrenheit, and will be completely unable to move at 40 degrees. As
temperatures fall in the north, the sources of nectar also disappear,
providing a further incentive to seek warmer climes. Monarchs from the
Western side of the Rockies travel to coastal groves in California (the
Eastern Monarchs go to Mexico.)
San Diego is fortunate to host butterflies taking shelter in eucalyptus
and pine trees. Monarchs cluster together when roosting, overlapping
their wings with the next butterfly like roof shingles. Clustering
provides protection from the wind and rain and keeps the butterflies warm.
After a winter of inactivity, the Monarchs become more active in
mid-February and begin mating. By March, they're on their way to their
summer homes. Along the way they mate and lay eggs, and each new generation born also heads back to their ancestor's homes. Scientists have yet to learn how the butterflies know where to go. Unlike those passing
whales, no Monarch in San Diego has ever been here before. Each Autumn's arrivals are the great-great-grandchildren of the previous winter's
residents.
How can we help the Monarch refuel and refresh? Plant milkweed!
Milkweed is the critical larval food plant, the only plant that a Monarch
will lay its eggs on. It gives the Monarch its source of protection from
predators; the milkweed sap ingested by the larvae make both the
caterpillar and the butterfly toxic to birds. Plant nectar flowers for the
adults, particularly fragrant purple, yellow or orange ones with wide
petals (like a daisy) that provide easy landing pads. And if you do see
them roosting in a tree, don't disturb their rest.
Wintering areas for the Monarch in San Diego County:
Balboa Park: Grape St. Park
Carlsbad: Haas Grove
Chula Vista: Eucalyptus Park
La Jolla: Pottery Canyon and the UCSD campus
Old Town: Presidio Park
Solana Beach: San Dieguito Park
Butterfly Garden
Have you ever heard that butterflies like pizza? It's not the cheese
and tomato sauce that attracts them; it's the shape. Pizza-shaped
flowers like daisies, asters, cosmos, coneflowers, and zinnias offer a
butterfly a wide landing pad and easy access to their nectar. Other
favorites are sage, lantana, lavender, milkweed, and ceanothus. Growing
nectar plants will ensure you'll get some butterfly visitors.
To keep them around longer, you'll need to add a few butterfly
luxuries. A rock in full sun and sheltered from the wind provides a place for
butterflies to bask in the sun. Male butterflies enjoy a mud spa: they
like a wet muddy place where they can pick up minerals from the soil.
The ultimate attraction: babysitting service! Offer a female a place
to lay her eggs by planting the larval food source for the caterpillars.
These plants will provide the food and shelter for the next generation.
Your final responsibility is to stop using any pesticides. Even
organic solutions like BT will kill the butterfly caterpillars along with the
pests. Let the birds feast on your unwanted insects.
For a full list of native plants used by our local butterflies, see the
websites below, especially http://www.laspilitas.com/butterfl.htm
which also includes links to detailed butterfly and plant descriptions.
Field guides are also good sources for finding the larval food plants, but
must be used with some caution as they may include plants that are
invasive in the San Diego region. Lists of plants for butterfly gardens
often include wild fennel (foeniculum vulgare) for the anise swallowtail
and passionflower (passiflora caerula) for the gulf fritillary. Please
do not degrade San Diego's native habitats by planting these species.
Alternatives are listed in the websites recommended below. Invasives
have no trouble spreading from gardens to the wild: their seeds hitch
rides on you, animals, the wind, and water; their cuttings will take root
beyond your control. When in doubt, check the California Invasive Plant
council website http://www.caleppc.org/ before planting.
Butterfly Links:
Illustrated Butterflies of San Diego County
San Diego Natural History Museum species list
USGS Species List
Butterlies and their Larval Food Plants (UC Irvine)
Plants for a California or Western Butterfly Garden
Monarch Watch
Painted Lady Butterfly Migration
Butterflies and their Larval Food Plants
North American Butterfly Association
The Xerces Society for Invertebrate Conservation
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