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Doug
Tallamy has a message for gardeners: let the bugs eat. From an insect’s
perspective, there’s no such thing as pest damage. A leaf riddled with holes is
a good sign: it means that the food
chain is working.
Tallamy,
professor and chair of the Department of Entomology and Wildlife Ecology at the
University of Delaware, has just written a new book called Bringing Nature
Home: How Native Plants Sustain
Wildlife in Our Gardens. (Timber Press, 2007) In it he makes a compelling
argument that gardening for birds and other wildlife begins with planting what
insects like to eat—and letting them eat it. “Ninety-six percent of terrestrial birds in the United States rear their
young on insects,” he said. “Insects
take the energy that plants grab from the sun and they release it into the food
web. People think about feeding birds berries and seeds, but they really need
insects. In one day, a pair of bluebirds will feed three hundred caterpillars
to their young.”
That’s
enough to convince me. But I’ve already
planted flowers and shrubs that produce pollen and nectar, and I see plenty of
bees, butterflies, and tiny winged creatures enjoying the buffet. Isn’t that enough?
It’s a good
start, but herbivorous insects like caterpillars, crickets, and beetles need
leaves to munch on, and they prefer the leaves of native plants. Many insects
are simply unable to digest some of the compounds found in exotic, imported
plants, and Tallamy explains why: “Many
of the plants that have succeeded in North America are not a random sample of
plants that evolved elsewhere, but rather are a subset that were imported
specifically because of their unpalatability to insects.” Ah-ha! Some of those delightfully pest-free
ornamentals that gardeners love are actually impossible for our insect
population to digest. Privet, Bradford
pear, lantana, English ivy, and wisteria are just a few examples of ornamental
plants that bugs rarely nibble.
“Our
insects have not had a long evolutionary history with these exotic plants,”
Tallamy said, “so they can’t break down chemicals in those leaves. On the other hand, take our native
milkweeds. Monarch caterpillars can break
down the cardiac glycosides found in that plant, and it’s a good food source
for them. Remove the milkweed, and the
caterpillars don’t have option of crawling off to nearest oak tree.”
Ultimately, Tallamy says, we seriously reduce insect biomass when we bring in
alien ornamental species. And that
reduces the amount of bird food out there.
What should
you plant? If you’ve got the space, nothing beats a native woody tree or
shrub. Oak trees play host to an
astonishing 534 species of butterflies and moths. Willows, cherry and plum trees (there are 31 native species),
birch, and poplars each host over 400 species. Even blueberries and cranberries make great choices, offering tasty
foliage and fruit, and thriving in acidic soil. Pines also harbor a number of
tasty caterpillar; Tallamy remembers watching a pair of bluebirds in his backyard
rear their first clutch of youngsters almost exclusively on the sawfly larvae
inhabiting his white pine. “Without those white pines, they would have had
clutch failure,” he said, “because there was no other insect population
available right then. And there aren’t enough woodlands left to support our
bird population. It’s got to happen in
suburbia.” He urges gardeners to understand that their garden now has to play
an important ecological role that it didn’t have before bird habitats were
destroyed. The key is to find the
particular species that is well-suited to your microclimate and your local
fauna; a good native plant nursery is likely to have the best selection.
But
choosing the right plants is just part of the process. It also helps to start looking at bugs as
bird food rather than as pests. Leafhoppers are almost too small to see, so you might not even realize
that swallows are gobbling them up by the hundreds. Spittlebugs also make a
tasty meal, and while it’s tempting to blast off the foamy ‘spittle’ that
shelters the half-grown nymph, the fact is that the bugs do little harm to
plants and the ‘spittle’ goes away on its own at the end of the season. Even aphids are not as bad as they seem:
dragonflies and bats will pick them off, and those that do survive are a food
source for lady beetles and other predatory insects.
Once it
becomes clear that a bug-ridden garden is actually the equivalent of a
four-star restaurant for birds, it becomes a little easier to tolerate those
holes in the leaves. Besides, Tallamy
points out, “the plants will not be destroyed by bugs. You’ll create a diverse ecosystem, where
natural enemies, including birds and other insects, will keep things in
balance. Your garden won’t be defoliated, and if it is, you’re probably dealing
with an alien insect that has moved here without its natural enemies.” To find out, try to catch the bug in the act
and clip a section of a branch while the critter is gnawing on it. Seal it in a plastic bag and take it to the
garden center or county agricultural extension office for identification.
If you are dealing with an exotic
invader, organic and less toxic controls are available, including pheromone
traps, insecticidal soaps, and biopesticides made with beneficial
microorganisms like Bt (Bacillus thuringiensis). But even those controls should only be used
as a last resort. Even exotic pest
infestations go through cycles, and if you can tolerate the damage and wait it
out, you may find that next year is easier.
And remember—you’re the one calling the shots
here. Don’t let somebody else’s idea of
beauty get in the way of a lively, wildlife-friendly garden. “Your garden is
the one piece of land that you can control,” Tallamy said. “From a selfish perspective, we need
biodiversity. We are not going to exist on this planet as the only species. We
have taken so much habitat for our own use. If we don’t share those spaces, we will lose species. But if we can rethink how we landscape, we
give these creatures someplace to go.”
So what works in a California
garden? Here are some of my favorites:
Pacific dogwood (Cornus
nuttallii) This gorgeous dogwood
demands very little in the way of routine care. In fact, it is downright offended by regular garden watering,
fertilizing, and pruning. Its bark is
tender and any cuts along small branches could provide a way in for diseases or
pests. Plant in well-drained soil and
water infrequently once established.
California lilac (Ceanothus
spp.) Californians are lucky to have a wide variety of ceanothus to
choose from. These tough, evergreen
shrubs produce clusters of tiny lilac flowers, provide cover for birds, and
give many insects something to graze on. Some varieties grow so low that they can almost be called groundcovers,
while others reach the size of a small tree. Too much summer water can cause some varieties to rot, so if you are
planning to plant one in the perennial garden where other plants need
supplemental water, choose a reliable garden favorite like C. thyrsiflorous
repens ‘Creeping Blue Blossom.’
Coyote brush (Baccharis
pilularis) I admit that it takes an ardent native plant lover to appreciate
this shrub. It’s a tough, dense shrub that will tolerate almost all of
California’s weather extremes and play host to an astonishing array of insects
and birds. Plant it on a slope, at the
edge of your property, in a hedgerow, or anywhere you can use reliable green
color with no water or fertilizer. Native plant lovers know to plant a male and
female variety; although the females produce seed clusters that look like bits
of cotton, it won’t seem at all messy in a semi-wild landscape.
Manzanita (Arctostaphylos
spp.) If you can’t find a manzanita
to love, you’re just not trying. These
native evergreens are admired for their smooth bark and intricate branches, but
also for their clusters of white and pink flowers followed by summer berries
for birds. I particularly like A.
densiflora, or Vine Hill manzanita, a northern California native that grows well
on banks and slopes.
Milkweed (Asclepias
californica) If you don’t have room for a tree or shrub, you can still
watch the bugs munch on your plants if you choose one of the many native
California milkweeds. Contact your
local native plant society to find out which variety is favored by your local
butterfly larvae. Plant several in a neglected corner of the garden, and
wait. If you’re lucky, you’ll see
monarch butterflies dance through your garden and leave eggs on the leaves.
Eventually those eggs will become voracious caterpillars that rely on the
leaves as their sole source of nutrition. They’ll form a chrysalis right on the plant and then emerge as a
fully-formed butterfly.