Butterflies and Larval Food Plants

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Photo courtesy Fotolia/abet
At the start, new butterfly gardeners concentrate on attracting adult butterflies by adding nectar plants to their landscapes. But curiosity and logic soon drive them to wonder about the other side of the life cycle, and that’s where the fun really begins.

WARNING! Butterflies can be
addictive!

So say many new books on butterfly identification, and the
number of “butterfliers” to join the sport in
the last decade seems to confirm this. A new style of field
guide that allows identification on
the fly, rather than requiring the butterflies be netted
and killed, is partly responsible. Anyone who has used a
bird guide will be comfortable with this method, and with
using a pair of short-focusing binoculars that allows you
to study a butterfly as close as your foot without scaring
it away.

At the start, new butterfly gardeners concentrate on
attracting adult butterflies by adding nectar plants to
their landscapes. But curiosity and logic soon drive them
to wonder about the other side of the life cycle, and
that’s where the fun really begins.

Gardeners and other plant lovers often find the study of
butterflies particularly rewarding because it offers
fascinating glimpses into why plants are the way they are.
Like most herbivores, butterflies have a preferred meal
plan — in fact, many species are so finicky about
their choice in food plants for their caterpillar stage
that their survival rates rise and fall on the success of a
single plant species. The coevolutionary dance between
plant and insect is an amazing story of defensive
strategies attempted, overcome, improved and overcome once
again.

Plants “retaliate” for being chomped on by
developing special poisons or distasteful chemicals. We
humans have many reasons to be grateful for this process
— the herbivore pressure on plants has led to
wonderful adaptations, both medicinal and flavorful. Mints,
oregano, spicy nasturtium leaves and pine resin are good
examples. Most of the aromatic smells, unique tastes and
medicinal properties we enjoy in plants came about as
defenses. Butterflies are only the visible tip of the
iceberg when it comes to the world of insect herbivores
driving these botanical experiments — but they are so
wonderfully visible!

Plants’ chemical-defense plans generally work, but
eventually an insect comes along that finds a way to
neutralize the poison, or better yet, put it to a good use.
The relationship between monarch butterflies and milkweed
is a celebrated example. The poisonous glycosides in
milkweed repel most herbivores. But monarch caterpillars
not only eat the leaves, they harmlessly store the
glycosides on into adulthood. Birds learn quickly to avoid
these brightly colored butterflies after the first vile
taste.

Over time, as the plant ramps up the concentration of the
compounds, the insect eating it adapts. But success comes
at a cost — eventually, the butterfly becomes
dependent on those compounds, which it needs to trigger
both egg-laying behavior and larval feeding. Apollo
butterfly larvae eat stonecrop and store for defense a
compound from it called sarmentosin. Red admirals nibble
safely on nettle leaves. Pearl crescents need asters.
Fritillaries only eat violets (though you won’t catch
them at it since the caterpillars retreat into the ground
during daylight). Skippers cue in on grasses. Cabbage
whites eat, well, cabbages. (Leave the Bt spray off one of
your cabbage or broccoli plants to encourage those
delightful butterflies.) And so it goes, for most
species.

With the exception of a few butterfly species that migrate
in, it is the presence of larval food plants that generally
determine local butterfly populations. These plants are
almost always native to the area. If your yard and garden
consist of mowed lawn and non-natives, you probably
aren’t offering much larval habitat. You can remedy
that by dedicating an area to host plants — a good
field guide will help you figure out what plants your local
butterflies use. Leaving parts of your property in a wild,
untended state is probably one of the best things you can
do for these beauties. And unless you have a specific pest
problem to control, ignore gardening advice that says to do
an autumn cleanup to remove all dry leaves and perennial
stalks — it is just those protected places where
caterpillars and chrysalides spend the winter. Not only
will you have better butterfly habitat — you will
have more time to sit still and be enchanted by the
spectacle of butterfly life. 

Marvelous Milkweed

You can attract monarch butterflies to your yard by
planting a patch of milkweed, a very easy-to-grow native
perennial that produces seed pods with those downy white
tufts many of us love to set free on the wind. And
you’ll get a bonus if you grow milkweed: The young
shoots and flower buds are edible, plus the unique fluffy
floss in the mature seed pods makes a superb alternative to
expensive goose down for use in insulated vests, jackets
and even comforters.

You can boil young milkweed shoots and leaves for an
asparagus-like vegetable. (Avoid mature leaves and stalks,
which are bitter.) Young flower buds and very young pods
have a pealike flavor. The flowers can be used as a
thickener for soups and can be boiled down to make a sugary
syrup.