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If you have a lot of flowers in
your garden, chances are that they will be visited by a delightful
moth known as the hummingbird sphinx. At first sight, you might think
you are seeing a small hummingbird hovering above your flowers. Look
a little closer and it becomes clear that the critter visiting your
flowers is a moth, not a hummingbird.
Also, if you happen to be a vegetable gardener and grow tomatoes,
you might wake up one morning and find that your tomato plants have
been stripped of their foliage. Look closer and you may find one or
two large green caterpillars, each adorned with a rear horn-like appendage.
Your tomatoes have fallen victim to a common garden insect: the tomato
hornworm.
Both the hummingbird sphinx and tomato hornworm are members of a large
family of moths known as the Sphingidae. They are commonly known as
sphinx or hawk moths and the larvae are known as hornworms. About
1200 species of hawk moths are known worldwide. They are most common
in tropical regions, but many species are found in temperate climates
such as Colorado. The adult moths are moderate to large in size and
have narrow wings and a streamlined abdomen. These are adaptations
for rapid, sustained flight. Hawk moths are actually the strongest
fliers of all moths and some species are capable of flying at speeds
over 30 miles per hour.
The hummingbird sphinx can hover in mid-air while it feeds on nectar
from flowers. The ability to hover has evolved only three times in
nectar-feeding animals: hummingbirds, certain bats and certain species
of hawk moths.
The caterpillars, or larval stage of hawk moths, are large to medium
in size with some species growing to over three inches long when mature.
Usually their bodies lack hair or tubercles, but most hawk moth caterpillars
have a distinct “horn” at the posterior end of their bodies.
Many species are green or brown in color and can easily blend in with
their surroundings. Like the tomato hornworm, the larval stages of
hawk moths feed on foliage. A species closely related to the tomato
hornworm feeds on tobacco leaves and is known as the tobacco hornworm.
The caterpillars of the white lined sphinx, the most common hummingbird
sphinx in Colorado, feeds on a variety of plants such as portulaca,
primrose and wild grape but seldom causes significant damage.
Many people have a natural fear of hornworms because of their large
size and posterior horn, which looks like a stinger. Yet these caterpillars
are totally harmless, except for a personal experience I had in North
Carolina many years ago. I walked through a tobacco field and unknowingly
brushed up a against a tobacco hornworm larva, which eventually crawled
up my leg on the inside of my pants. Several hours later, when I was
driving home, something bit me in the leg. After I recovered control
of the car and stopped, I shook out my pants and out fell a large
green hornworm.
On the Caribbean Islands of Trinidad and Tobago, a striking hornworm
feeds on the foliage of the fragrant frangipani tree and the large
African milkweed that has been introduced to these islands. To my
entomologist’s eye, this is one of the most beautiful caterpillars
I have encountered. The body is black with bright yellow vertical
bands, a red head and orange legs and prolegs. The local people believe
that contact with these caterpillars causes fever and kill them every
chance they get.
This fascinating group of insects has many species, such as the hummingbird
sphinx, which are a special treat to have hovering among your flowers,
or the tomato hornworm, which can cause severe damage. On a positive
note, tomato hornworms are easily controlled. You can simply remove
the caterpillars from infested plants. I have tossed them onto the
lawn and had them picked up by passing birds. Tomato hornworms are
also highly susceptible to the bacterial insecticide Bacillus thuringiensis.
Illustrations (all taken by the
author, Bill Ciesla)
1. A hummingbird sphinx moth in a rare moment of resting allowed me
to capture this photo (hummingbird_sphinx_bw).
2. This hawk moth, which I encountered
in Cancun, Mexico illustrates the narrow wings and streamlined abdomen,
which are adaptations to fast and prolonged flights (hawk_moth_cancun)
3. The frangipani hornworm of Trinidad
and Tobago is a striking example of the larval stage of hawk moths (frangipani_hornworm).
4.
This photo of the sphinx moth was taken in my backyard garden (sphinx_moth3).
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