CHAPTER 15
Butterflies
and Moths
This is one of
the most popular orders with amateur entomologists because it contains many
large and beautifully colored insects. Lepidoptera means,
"scaly-winged." Of the approximately 135,000 species in this order,
24,000 are butterflies. Butterflies and moths are very much alike. In fact,
butterflies descended from moths. Generally speaking, butterflies are colored
more brightly than moths. The reason for this is associated with the time of
day when each group is active. Moths usually are nocturnal while butterflies
typically are diurnal. Butterflies, being day-fliers, rely on their bright
colors to attract individuals of the opposite sex. Because moths are night
fliers and because it is more difficult to perceive color in reduced light
intensities, moths do not rely on sight to find the opposite sex but use odor
or sex pheromones instead.
An additional
difference between butterflies and moths is the shape of their antennae.
Butterfly antennae typically are thread-like and usually terminate in a small
knob or ball. In many cases moth antennae are much more elaborate, frequently
appearing comb-like. This difference may be due to the fact that moths rely on
odor to find the opposite sex and therefore need more elaborate (efficient)
antennae.
The
mouthparts, or proboscis, of adult butterflies and moths consists mainly of two
"soda straw" appearing structures (modified maxillae) that are
capable of being rolled up or unrolled when feeding on liquids such as nectar
or drinking water.
KILLING BUTTTERFLIES TO SAVE THE RAINFORESTS
As previously
mentioned there are many amateur entomologists around the world who collect and
buy butterflies and other insects for their private collections. There are
people who would object to this practice, suggesting that it is the use of
nature for one’s own personal pleasure. And it is well documented that
butterflies and other insects are beginning to disappear from many areas,
including the tropics of the world. However, it is also documented that the
collecting of insects has had little, if any effect, on the total population in
any given area. The disappearance of plant and animal species from temperate
and tropical areas of the world can be attributed to the destruction of their
habitat. The authors estimate that the cutting of one large rainforest tree may
kill a million or more insects.
There have
been many different projects attempting to save the rainforests of the world.
Unfortunately, most of these have had little, if any effect on this decimation.
In most cases the underlying reason for these failures seems to stem from human
encroachment into these areas in attempts to acquire capital gains or merely
provide the essentials of survival. Two of the main practices that result in
rainforest decimation are forest clearing for conventional farming practices
and logging. It is difficult to condemn either of these practices because
typically both provide money and food for the individuals who inhabit or own
the forests.
The government
of Papua New Guinea instituted one program that has had considerable success.
They established a central agency, the
The principle
idea behind this program was to make the forest of
Figure
15A. A box of Ornithoptera birdwings that were farmed by the natives of
Papua New Guinea.
Estimated collector value, $1,000.
The natives raise enough money from this
practice to buy the few western goods they desire and to pay the taxes for
their children’s schooling. The forest remains intact for hunting of food and
there is little need to turn to agriculture. Papua New Guinea's people
primarily are hunters. The insect population in this island country has changed
little since this program was initiated. It is too bad that this can’t be said
for other tropical countries. Actually butterfly farming is becoming more
common in many tropical areas of the world because it is a solution that is
good for the people of the rainforests and for those interested in maintaining
what remains of the world's forests.
THE SILKWORM
Although there
are several species of silkworms, Bombyx mori is the one used almost
universally for silk production (Figure 15B). The discovery of the use for this
species for commercial silk production occurred in China about 2,700 B. C.
Chinese legend states that a great prince directed his wife to study the silk
moth and its potential for making cloth or silk. She not only discovered the
means of raising Bombyx mori on mulberry leaves but also the manner of
reeling the silk strand from the cocoon to make thread. She was later given an
honored name, Seine-than, or "The Goddess of the Silk Worm". Silk
production subsequently spread through China and became a very valuable
commodity throughout the world. The secret of silk production became a very
closely guarded secret in China with the leakage of this secret punishable by
death.
Figure 15B. An adult male silkworm moth.
By the first
century A. D., the origin of silk was still protected by the Chinese. Early
writing of the Roman Virgil speculated that silk was produced from the fuzz of
leaves. Considerably later (300 AD) the secrets of sericulture were leaked from
China into Japan by a Chinese princess who carried the eggs of the moth and
seeds of mulberry in her headdress and later into Rome by a monk who carried
the same in a hollow staff.
With China’s
monopoly on silk production broken, importation from China became less and
less. In 877 A. D. a rebel chief raided the city of Canfu, the center of
foreign silk production in China, killed all of its inhabitants, destroyed all
the mulberry leaves and silk moths and imposed very high taxes on foreign
trade. This stopped foreign trade on silk in China for over one-half century.
However, by that time silk production had become fairly widespread in the world
and these actions had little effect on the price of Chinese silk. Asia still
remains the center of silk production today with countries like India, Thailand
and China leading the way.
Silk
production on a commercial basis has been attempted on several occasions in the
United States with limited success. In early colonial times, silkworm rearing
for the good of the British Empire was widespread. In fact, in some areas, it
was illegal not to raise them. The French had been doing quite well with
silkworm rearing and competition between Britain and France was in full bloom.
After the American Revolution, sericulture was still practiced by the new
American society.
In 1831, J. H.
Cobb published a manual on sericulture, which was purchased and distributed to
the U. S. Congress. This created great interest in the U.S. and eventually led
to what is known as the Morus multicalis craze. Anticipating immediate
riches, thousands of people bought large parcels of rather expensive land and
established huge plantations of mulberry trees of the above species. Because of
massive over planting and subsequent frost destruction of most of the trees,
these ventures still failed. However, because of the Civil War, cotton was not
readily available in the northern U.S. Consequently, there was still interest
in developing some type of fabric industry in the north.
Thus, in 1869,
Professor E.L. Trouvelot imported from France into Massachusetts some eggs of
the gypsy moth with the idea of finding a less host-specific moth (the silkworm
only feeds on mulberry) that could produce silk. Trouvelot's efforts to replace
Bombyx mori with the gypsy moth were a failure. The silk was poor
quality and the silkworms were hard to rear. Either during or after his
experimentation, some caterpillars escaped. Now this moth is spread throughout
most of the United State and its caterpillars are considered one of, if not the
most, serious defoliating pests of our forests.
The silkworm
possesses a pair of modified salivary glands, which are used to produce silk
for encasing the pupal stage in a cocoon (Figure 15C). These glands produce a
clear proteinacous fluid, which hardens into a silken thread when it comes into
contact with air. Over a 4-day period the last instar larvae produces the
silken cocoon for pupation. The caterpillar makes approximately 300,000 figure
eight movements with its head while producing over 900 meters of a continuous
silken thread to make the cocoon. This thread must be unwound prior to the
emergence of the adult moth. The pupae are typically killed by heat,
electrocution or microwaves and subsequently the cocoons are soaked in hot
water prior to unwinding the silken threads from the cocoon. Single threads are
combined to form yarn for weaving.
Figure 15C. The cocoon of silkworm pupae, the source of
silk fibers.
Silk production
is time intensive. The larvae feed solely on mulberry leaves and a larva eats
50,000 its initial weight in leaves to reach adulthood. It takes approximately
1,500 cocoons to produce one silk dress. The nourishment of 1,500 caterpillars
(Figure 15D) requires approximately 110 pounds of mulberry leaves. World silk
production has doubled in the last 30 years in spite of the availability of
man-made fibers. The current world production is about 160,000,000 pounds,
requiring almost 100 billion worms.
Figure 15D. Silkworm caterpillar feeding on mulberry
leaves.
BUTTERFLIES
There are
countless references to butterflies and moths in the mythology of many cultures
throughout the world. This is due primarily to these insects’ beauty, power of
flight and complete metamorphosis. In the interest of brevity we will restrict
our discussion to butterfly and moth mythology in North America.
The sheer
beauty of butterflies plays an important part in a legend of the Papago
Indians. According to this myth the creator felt sorry for babies when he
realized that their destiny was to become old, wrinkled, fat, weak and blind.
Consequently, he gathered beautiful colors from sunsets, rainbows, clouds,
flowers and the sky and placed them in a bag, which was presented to children.
When the bags were opened, butterflies flew out, enchanting the children who
had never seen anything so beautiful. If that wasn’t amazing enough, the
butterflies sang as they emerged from the bags but the songbird became jealous
because the butterflies were not only beautiful but could also sing.
Consequently the creator withdrew the butterfly’s ability to sing.
In a Motorway
legend of the Navajo, a bisexual god named Begochildi was leader of the
butterfly people and serviced the sexual need of both the male and female
butterflies. However, when Begochildi decided to leave the country, the
butterfly people decided to commit incest rather than marry outsiders. This
made the butterfly people go wild, which is today manifested in the tendency of
moths to wildly fly to a flame or light. The Mothway legend is to the Navajo an
explanation why sibling and clan incest is forbidden.
The Blackfeet
believed that butterflies bring dreams to us. A mother would paint the symbol
of a butterfly on a small piece of buckskin and tie this in the baby’s hair
when she wanted the baby to go to asleep. At the same time she would sing the
baby a lullaby to call the butterflies to put the baby asleep. It was felt that
if you looked long enough at the soft gentle flight of the beautiful butterfly
it would calm you to sleep.
Many of the
Hawk or Sphinx moths, such as the death head moth, emerge as adults from their
pupal cases several hours before embarking on their virgin flights in the
evening. Immediately prior to flight, these young moths exude a few drops of
clear red fluid (a by-product of pupal metabolism) called meconium. In some
cases, during peak seasonal emergence, it almost appears as though it is
raining blood from the sky. In Europe this situation of "blood"
falling from the sky has lead to the myth of a sign of impending war or other
disasters.
BUTTERFLY MIGRATIONS
A few species
of butterflies exhibit long seasonal migrations. Two notable U.S. species are
the monarch and painted lady butterflies. The painted lady is an orange and
black butterfly, which occurs throughout much of the world (Figure 15E). In
Western North America this species spends most of the winter months building up
its population with the caterpillars feeding on thistle in Northern Mexico. In
the spring, as their host plants begin to dry up, the adult butterflies begin
their northward migration, which eventually reaches Oregon, Washington, and
sometimes as far north as Canada. Individual butterflies do not typically fly
the 2000-mile trip but lay their eggs on host plants along the way. It may take
a few generations and several weeks to complete the trip.
Figure 15E. The painted lady butterfly, a well-known
migratory species.
Upon reaching
their destination, a few generations are completed in the north. In late fall a
few adults migrate back to northern Mexico to complete the yearly cycle. Some
years this spring movement is scarcely discernible. Other years the migration
is huge and it is almost impossible to look outdoors at any one time without
seeing several of these butterflies. The limiting factor appears to be the
availability of the thistle host in Mexico. If the winter rains in this area
arrive early and there is an abundance of this host, the migration will be
heavy.
The Monarch
butterfly has a similar migration (Figure 15F). However, because it is a native
to the southern states of the U.S., Central and South America, its migration
can be several thousand miles from South America into northern Canada. As do
all butterflies, they fly during the daylight hours and rest during the night.
It is not unusual for entire huge trees in the migratory path of these
butterflies to be so heavily covered with resting butterflies that their leaves
cannot be seen.
Figure 15F. The monarch butterfly is
perhaps the most studied butterfly in the world.
The exact mechanism of how migrating
insects navigate is not well understood. It is possible, at least in some
cases, that they follow prevailing winds.
DEFENSIVE MECHANISMS
Being larger
and therefore more visible insects, there are a number of predators that feed
chiefly on butterflies and moths. This is especially true with butterflies
because they are brightly colored and are day fliers. As one might suspect,
these insects have developed a vast array of defensive mechanisms. These
mechanisms are by no means limited to the adult stage. Many moths, upon
depositing their eggs, scrape scales off their bodies and wings to cover the
eggs—thus making them less visible to predators and parasites.
Caterpillars
(larval stage of butterflies) typically are plant feeders. Most of those that
feed on leaves are green in color, incorporating the chlorophyll from the
leaves into their bodies, thus giving themselves a significant degree of camouflage.
In addition, a few caterpillars bear urticating, or stinging, hairs (Figure 15G).
A classic example of this is the saddleback moth caterpillar. This caterpillar
is adorned with long stinging hairs. I once collected this species in northern
Thailand. I had read about urticating hairs but had never had the
"pleasure" of experiencing their effect. Being interested in
experiencing this I picked the caterpillar out of my net with my fingers. Bad
idea! The resulting effect was much quicker and more painful than that of a
hornet sting. It was almost as though a severe electrical shock shot through my
hand. Now that you are an educated entomologist, it should come as no surprise
that this caterpillar is distinctly marked with a bright red head with most of
the body a brilliant green encompassing a large red spot and fringed with a
gold outline for good reason. Great warning colorations. To make matters worse,
that evening we were driving up Doi Suthep (a mountain) looking for walking
sticks, tarantulas, giant millipedes or any other creature we might pick up
crossing the road in our headlights. After catching about 6 12-inch millipedes
we stopped for what I thought was another millipede. Instead it was the biggest
caterpillar I had ever seen (at least 9 inches). Without thinking that this was
a pretty hairy critter, I picked it up and, of course, the resulting effect was
about twice as bad as that of the saddleback. To this day we have not been able
to identify this caterpillar to even family level, although I have the pleasure
of knowing it is soaking in alcohol in our museum.
Figure 15G. Top-Left. An unknown species of caterpillar
illustrates bright warning coloration and urticating hairs located on the back
area of the abdomen (looks like small sea urchins). Top-Right. A puss caterpillar one of the better known
caterpillars with urticating hairs.
Image courtesy of CDC. Middle-Left.
Image Courtesy of Peter Chew, Brisbane Insects.
Middle Right Saddleback moth.
Image courtesy Gerald Lenhard, Bugwood.
Bottom Hag Moth caterpillar.
Image courtesy Jerry Payne, USDA, Bugwood.
Because the
pupal stage of most Lepidoptera is found below ground, it is not readily
available to most predators and parasites. However, butterflies are actively
sought by many. It might be thought that their bright coloration would be a
distinctive disadvantage for survival. However, the wings of butterflies
typically have bright colors on the upper side while the underside is dull in
coloration (Figure 15H). As a result, when a butterfly is in flight, the
alternate flashing of bright and dull results in what is referred to as the
flicker effect. Apparently most predators need to focus in on their prey prior
to capture and the flicker effect impedes this ability—thus giving the
butterfly an added advantage to escape. Also, when butterflies are at rest,
they usually hold their wings folded together—thus not exposing the bright
colors and drawing unwanted attention.
Figure 15H. A Papilio ulysses butterfly from
Indonesia illustrates the
brightly colored upper side and dully colored underside of its wing.
In some cases
the bright coloration of butterflies works to their advantage. Of course, the
most famous example of this is the monarch butterfly that is bright orange
contrasted with black stripes. In this case, the larval stage feeds on
milkweed, which contains some rather toxic materials. These toxins do not harm
the caterpillars but are incorporated into their bodies and in turn are passed
on to the adult butterflies. Any predator, such as a bird, feeding on either
the monarch caterpillar or butterfly, quickly learns not to feed on these
distinctly marked insects. In most areas where this species occurs, there is
another species called the Viceroy butterfly, which is colored almost exactly
the same as the Monarch. The caterpillar of this species does not feed on toxic
plants and both the caterpillars and butterflies of this species are totally
palatable. Predators rarely eat Viceroys, however, due to their resemblance to
the toxic monarch. Such a situation where one harmless species mimics the
appearance of a more dangerous species is referred to as Batesian mimicry after
the English scientist who first discovered the phenomenon.
The wings of
some butterflies lack the scales (clear winged butterflies) and are totally
see-through (Figure 15I). I first came across a number of these butterflies
when collecting in a rather dense forest in Costa Rica. The lighting in this
area was dim and it was very difficult to see the butterflies in flight as they
blended in totally with the background (you couldn’t see the wings). This
mechanism was very effective as there were hundreds in the area, but I, being a
very smart and agile predator (at least smarter than a bird, maybe not as
agile), could only find and catch a few.
Figure
15I. A clear wing butterfly, lacking the scales that normally give coloration
to the wings.
Image
courtesy of Butterfly Farm, San Jose, Costa Rica.
Many moths and
butterflies possess eyespots on the hind or underwings (Figures 15J). Obviously
the function of these structures is to suddenly appear when the hindwings are
exposed and function to startle a potential predator. A number of scientific
experiments have been conducted to substantiate the validity of this technique.
Predators greatly change their feeding activity when confronted with mere
drawings of two circles (simulating eyes) as opposed to squares. When a
predator is confronted with the owl butterfly’s underwings, one can only
imagine its reaction. It is amazing how nature has mimicked not only the eyes
of an owl in this case but the entire face.
Figure 15J. The underside wings of an owl
butterfly illustrating
the perfect face of an owl on the hindwings.
Finally a few
butterflies and moths possess long trailing tails on the hindwings (Figure 15K).
Although these structures may serve as keel for balance in flight, it is also
probable that they function as false targets. Many a bird has ended up with
nothing but a pair of broken tails when attempting to catch one of these
critters. Once broken off, these structures are not regenerated but one near
escape of death is better than none.
Figure 15K. Right.
Luna moth. Left. An Indonesian
giant silkmoth with long tails.
As discussed throughout this text it is not uncommon for
the insect to include other species for defense. Although rare this behavior can extend between
insect and other animals of totally different groups, including mammals.
Although rare a few species of moths communicate with bats. Some insect-eating
bats use echolocation to find their prey. A feeding bat sends out a high
frequency beep that bounces off its prey (moths), with the returning beep being
detected by the bats large ears. This system works similarly to a destroyer's
sonar in detecting a submarine. Some species of moths are capable of detecting
the beep of an echolocating bat. If the detected beep is weak, indicating the bat
is far away, the moth will fly away as fast as it can in an attempt to avoid
the bat. When the beep is strong, indicating that the bat is close, the moth
will fly erratically or merely drop to the ground. Although amazing, none of
the above is a good example of one species protecting another. However, in at
least one species of tiger moth, the beep of an echolocating bat will cause the
moth to return a squeak of its own, which is detected by the bat. This tiger
moth is foul tasting and any bat that has previously fed on another squeaking
tiger moth will associate that sound with the foul taste and break off the
hunt.
Unfortunately, a few questionable entrepreneurs have
exploited the public by selling pest control devices based on the principle of
avoidance displayed by insects and other pests upon hearing certain types of
sound. One such device is a small electrical box that is supposed to produce a
high frequency sound that drives cockroaches and other insect pests from the
home or disrupts their mating biology. Another is a probe that, when placed in
the ground, produces a beep that drives gophers from the ground. Unfortunately
these devices are totally worthless. I once walked into the backyard or a
homeowner who had placed eight of these probes in the ground in attempts to
eliminate one gopher. Of course the gopher was still there after 4 weeks of
beeping.
Although rare, there have been a few documented cases of
one species of insect communicating with another species of insect. There is a
species of caterpillar in Costa Rica that possesses glands, which secrete a
sweet tasting fluid that readily attracts ants to feed on the liquid. The ants
obviously benefit from the relationship by obtaining nutrients from the liquid
and the caterpillars benefit by the ants' protection from potential predators.
The caterpillar has a ridged area on the front of the thorax which, when rubbed
by the back margin of the head, produces a squeaking sound. If a predator
attacks the caterpillar, it produces this sound, which alerts any nearby ants
to the danger.