1998 / 10月
Chang Chin-ju /photos courtesy of Vincent Chang /tr. by Robert Taylor
In a TV advert, a stream of colorful, flut-tering butterflies reminds people in Taiwan not to ignore the fact that butterfly valleys all over the island are at risk. But while many voices call on us to save Taiwan's butterflies, few seem concerned about their close cousins, the moths. It was not until this summer, when hordes of hungry caterpillars invaded many school campuses, plant nurseries and roadside trees, stripping branches bare of leaves and causing red itchy swellings on hundreds of people's skin, that moths finally made it into the news in a big way.
The larvae of butterflies and moths are all called caterpillars. But why should caterpillars "strike back" in this way?
"Tiger moth caterpillars are causing havoc in Wenhua Lane, Kenting. They have so far defeated all the town council's efforts to exterminate them. . . ."
"In areas of Taitung City such as Hsuchou Street and Kuangtung Road, unidentified black caterpillars are eating the leaves of castor-oil plants on a vacant lot. Every day at dawn and dusk they swarm over walls and crawl into neighboring houses in frightening numbers, coming in under doors and through windows. . . ."
Caterpillars invading houses? Caterpillars "defeating" efforts to eradicate them? Caterpillars in "frightening" numbers? In newspaper reports from different parts of Taiwan, wriggling caterpillars are described as if they were the mutant monsters of horror films, preparing to attack the human race in relentless waves with bared fangs and flailing claws.Unwelcome guests
This summer, from Taitung City in the east and Pingtung County in the south to Nantou County in central Taiwan and Hsinchu County in the north, caterpillars spread like wildfire, leaving trees bare and ugly.
Old Mr. Wu Kun-po of Puli in Nantou County had planted over 1000 square meters of land with emerald-green Podocarpus formosensis trees. In June, he came back from a holiday trip overseas to find his plantation reduced to an expanse of bare, dying tree trunks covered in thousands of matchstick-like inchworms-caterpillars of the inchworm moth species Milionia basalis pryeri. The grubs' little round heads waved from side to side as they busily chomped their way through the last remaining leaves. Many, unable to find any more tender leaves to munch on, were hanging by long silken threads, waiting for the wind to swing them across to other trees; others arched their backs and wriggled off over the field embankments and into people's gardens.
Before the summer holidays, at Nanliao Elementary School on the coast of Hsinchu County, a grove of five or six bishopwood trees (Bischofia javanica) over two stories tall were rapidly stripped of their leaves by caterpillars of the two-spotted lymantriid moth (Euproctis bipunctapex), which left them as bare as if swept by autumn gales. Today, the bishopwood trees, which have been pruned back to a story tall, have sprouted foot-long new leaves. When a workman waves a long pole through the treetops, dozens of caterpillars come tumbling down. The onlookers immediately jump back out of the shade of the tree-they still have fresh in their memories how the spiny hairs on the caterpillars' bodies caused the skin of all the school's more than 500 pupils and teachers to swell up in an incredibly itchy red rash, so that the school had to be closed for two days. At the same time, two-spotted lymantriid moth caterpillars also went on the rampage at Chu-nan Elementary School in neighboring Miaoli County, ravaging the school's more than 50-year-old bishopwood and maple trees.
Among the world's million or more known insect species, the order formed by the moths and butterflies-called Lepidoptera (from Greek lepido-, "scaly" and ptera, "wings") for the often brightly-colored scales which cover their wings-accounts for a substantial proportion in terms of both populations and number of species. It is the second largest of the more than 30 insect orders.Butterflies good, caterpillars bad?
The larvae of moths and butterflies are called caterpillars. Their name in Chinese-maomaochong-means "hairy grubs," and in fact the English word caterpillar also comes from Old North French cate pelose, meaning "hairy cat." But although many caterpillars do have a dense covering of fine hairs on their bodies, some are covered with fleshy spines, while others have completely smooth skins. Lepidoptera larvae, which amble along at a leisurely pace with undulating bodies, come in a tremendous variety of shapes and sizes.
Most people who grew up before the 1970s or '80s have memories of "close encounters of the first kind" with caterpillars. But as green spaces have gradually disappeared from people's lives, opportunities to see caterpillars in the cities have grown fewer and fewer, and biologists have even recommended that many butterfly and moth species be placed on the protected list. So why did the numbers of caterpillars in many places explode to such levels that they invaded people's homes?
In ecological terms, changes in insect populations are affected both by "biological factors," such as their natural enemies and host plants, and by "environmental factors," such as weather, soil and man-made pollution. The abnormal weather of recent years has gradually become the main suspect.
"Actually, we get caterpillars every year," says Liu Fang-yuan, head guidance counselor at Nanliao Elementary School. Every July and August, during the summer holidays, the several large trees in the school grounds become a caterpillar kingdom. But following unusually warm weather last winter, this summer the grubs reported for duty earlier than usual and in larger numbers, causing allergic reactions among the children. Only then were they perceived as a "pest."
At the same time, in the town of Kenting in Pingtung County, a hundred or more castor-oil plants (Ricinus communis) on a vacant lot several hundred square meters in area were stripped of all their leaves by tiger moth caterpillars (family Arctiidae). Chuang Ling-mu, a research assistant at the Hengchun research station of the Taiwan Forestry Research Institute (TFRI), says the warm winter caused trees to flower and fruit early, and the plentiful rainfall in May and June boosted plant growth. He speculates that these may have been "contributory factors" in the explosion in caterpillar populations.
Is climatic warming behind the sudden growth in insect populations? Most heterocerists (moth researchers) take the view that in the absence of research, this is "pure conjecture," for if the weather causes caterpillar numbers to rocket, it should have the same effect on other insects too.
TFRI researcher Chao Jung-tai, who over the past six years has traveled all over Taiwan doing tree pest and disease control work, says: "There really has been some increase in the number of cases reported to the TFRI this year." In the past, reports averaged three to four a month, but this year there have been over ten in two months. Moth larvae have not been the only pests: they have also included leafhoppers, whitefly and others.Less caterpillars, not more?
At present, there are no organizations or researchers in Taiwan doing long-term monitoring of relationships between the greenhouse effect, changes in rainfall, plant growth and changes in caterpillar populations. Hence there is no hard data to support the idea that the abundance of caterpillars is related to climatic factors.
Some people even argue that there has been a marked decline in the number of caterpillars this year. Generally speaking, insects are more abundant in the tropics than in cooler climes, and this naturally leads people to suppose that if temperatures rise, insect populations will increase. "But insects have adapted to high temperatures over long periods. That's not the same as rapid rises in temperature due to the greenhouse effect," says Chang Yung-jen, a nature photographer who recently published a two-volume introduction and field guide to Taiwan's insects. He notes that many caterpillars pupate during the winter, and they often need to be exposed to low or even sub-zero temperatures before they are "willing" to finish their pupation and emerge as adults. In his experience, when people bring caterpillars from Taiwan's medium elevations down to the plains to try to raise in captivity, the majority do not survive.
Evidently, short or warm winters and unseasonable cold or warm spells all upset the usual pattern of nature. "Climatic warming does not improve insects' chances of reproduction," says Chang Yung-jen. He even feels that the reduced rainfall this summer due to the small number of typhoons is affecting caterpillars' ability to pupate. "Many people who observe or photograph insects have the impression that caterpillar numbers are down this year," he says.
Recent surveys by butterfly watching groups in Taiwan have shown that this year in "Yellow Butterfly Valley" near Meinung in Kaohsiung County, where some 10 million butterflies usually appear over the course of the butterfly season from April to October, the numbers have fallen to only about 100,000, and of the 80 species normally found there, only 50 have been observed. Biologists' initial conclusion is that the lack of a clear distinction between the dry and rainy seasons in southern Taiwan this year is among the causes.Waxing and waning
Why is the reaction of field workers so different from the impression given by media reports?
Looking more closely at the recent spate of caterpillar incidents, we find that they all happened in school grounds, roadside trees, vacant building lots, seed nurseries and other places close to residential buildings, so that the caterpillars had the opportunity to crawl into houses and classrooms and come into "face-to-face conflict" with human beings. This, and a degree of sensationalism in media reporting, gave the impression that caterpillars were rapidly growing so numerous that they were about to "occupy" the whole island.
In fact, out in the natural world, caterpillar swarms are far from unusual. Most Lepidoptera larvae feed on plants' leaves, fruit, or flower buds, and their main mission in life seems to be to get their heads down and eat for all they are worth. "Biological factors" such as a fall in the population of their natural enemies or unusually lush vegetation can quickly cause their numbers to get out of control.
Students and teachers in entomology and plant pathology departments have much experience of this. "Whenever we go out collecting specimens, we always see the treetops swarming with caterpillars," says Professor Yang Ping-shih of National Taiwan University's Department of Entomology. In fact, there's no need to ask the experts: "We used to see this kind of thing all the time," says Chiu Su-ching, a maintenance worker at Chu-nan Elementary School, where the bishopwood trees were infested with caterpillars this summer-as a child, she saw many such occurrences.
Furthermore, caterpillar population explosions usually end just as quickly as they begin. Fang Kuo-yun, a specialist in the Resources Conservation Division of the Council of Agriculture's Forestry Department, who went to school in Nanchou in Pingtung County in the 1960s, describes how at that time the classrooms were in rows of one-story buildings, alongside which were rows of tall trees. Often large swarms of caterpillars would suddenly appear and quickly eat all the leaves off the trees; but then big flocks of birds would arrive and feast on the caterpillars.
On nature's stage, the waxing and waning of different species and the supplanting of one by another is a scene which is constantly played out. Chao Jung-tai describes the schoolyard incidents as being part of a war between the insects and the plants. The insects mount a massive attack, which the trees are at first unable to fend off. But despite their initial victory, the caterpillars rarely have the last laugh. The trees are not defenseless weaklings: they protect themselves by chemical and physical means, and the caterpillars have all sorts of natural enemies too, from viruses, fungi and parasitic wasps which attack them from the inside, to birds which eat them wholesale. The grubs are also the victims of their own appetites, for once they have eaten all the leaves and fruit off a tree, starvation acts as a regulating mechanism, and their numbers fall dramatically.
The caterpillars of a very small number of moth species, such as Milionia basalis pryeri, may go on to eat the bark of trees once they have finished the leaves. But the vast majority of caterpillars do not "bite the hand that feeds them" in this way. Generally speaking, the next spring-or even after a month or two-the tree will sprout new foliage and be restored to its former glory.The dangers of monoculture
Fan Yi-pin of the TFRI's Division of Forest Biology, who often fields enquiries from schools as to what to do about caterpillars eating the leaves off their trees, recounts how a few years ago the banyan and pongamia (Pongamia pinnata) trees in the grounds of numerous elementary schools in Taipei City, Taipei County, Chiayi and elsewhere were infested with caterpillars of the clear-winged lymantriid moth (Perina nuda) and of Maruca testulalis, a pod borer. But this year when Fan telephoned schools to ask about the current situation, they all replied that there were fewer caterpillars than in previous years.
Thus it appears that within the small food chain of a school campus, caterpillar infestations will generally come under control sooner or later. But does this mean one can always simply sit back and wait for caterpillar attacks to pass?
Chang Jui-chang, who runs the TFRI's Center for Forestry Disease Control, points out that most trees in urban green areas and on school campuses have been propagated from a small number of parent trees, and their reduced vigor and immune resistance make them vulnerable to insect attack.
Chu-nan Elementary School is a good example. The school grounds used to adjoin a park, but today a 20-meter-wide main road has cut off part of the grounds to the left, while to the right some new houses have taken away part of the playground. The number of pupils has increased, but the school grounds have shrunk, and the areas where grass once grew are now all covered with polyurethane matting. The few large trees are ringed with concrete, depriving their roots of air. Hanging on to life by a thread, they have little ability to resist insect attacks. Hence the bishopwood trees, which are the commonest trees on school campuses, often become a breeding paradise for Milionia moths.
Human influences are certainly a factor in the occurrence of plagues of caterpillars. The swarm of inchworms in the podocarp plantation in Nantou County is a prime example. Podocarpus formosensis is a native Taiwanese podocarp, from the yellow-wood or Buddha's pine family (Podocarpaceae). Taiwan has seven native podocarps, but forestry experts do not recall ever hearing of them being attacked by such large numbers of Milionia basalis pryeri in the past.
Strangely, termites and the majority of other insects do not eat Podocarpus formosensis because of the special metabolites it produces; only M. basalis pryeri will touch it. But in natural forests, every creature has its natural enemies, and the insect fungus Beauveria bassiana and parasitic flies are ready and waiting for M. basalis pryeri. Furthermore, in the wild the inchworms prefer trees over two meters tall, and by the time trees have reached this size they are strong enough for a few caterpillars not to pose them any threat. Along the footpaths around Chihnan Temple in Taipei City's Mucha area, each of the scattered large podocarps has a few M. basalis pryeri living on it, but each is a match for the other and they coexist peacefully.Plant a tree?
In Taiwan, there was formerly no serious imbalance in the ecological relationship between podocarps and Milionia basalis pryeri, but on Japan's Ryukyu Islands M. basalis pryeri has become one of the most serious pests forestry workers have to contend with. Podocarps were introduced into the Ryukyu Islands to provide wood for Shinto shrines, but this created a golden opportunity for M. basalis pryeri to plunder the large monocultural podocarp plantations. Because of this, a cooperative program was once set up between the Ryukyu Islands and Taiwan to introduce natural enemies of M. basalis pryeri as biocontrols, and several international conferences were held between the ROC and Japan. But the program failed to produce any tangible results, and the same problem has since emerged in Taiwan. In recent times, nursery operators in Taiwan have seized on Podocarpus formosensis as a visually attractive and supposedly insect-resistant tree species, and planted it in large numbers. But a few years of planting have upset the equilibrium established over thousands of years, and tree nurseries have become the places where Miliona basalis pryeri has breached the podocarp's defenses.
Similarly, current efforts to promote a "plant-a-tree" movement have entomologists very worried.
In response to the global trend of rising levels of atmospheric carbon dioxide, the government is encouraging large-scale reforestation. But rapid planting of single-species forests in previously cleared areas implies that in the future, each such area will contain only one producer species, thus limiting biodiversity and creating incomplete and fragmentary food chains.
Examples of monocultural woodland being attacked by insect pests can be found everywhere. In our cities today, camphor trees (Cinnamomum camphora) grow everywhere, and the camphor scale insect is everywhere too, so that tree surgeons are rushed off their feet treating outbreaks. Planting large numbers of white popinac trees (Leucaena glauca) is a gift to jumping plant lice (family Psyllidae). Under Japanese rule, paulownia (Paulownia x taiwaniana) was planted widely, but after Taiwan's return to Chinese rule, paulownia trees throughout the island were simultaneously stricken with fungal leaf curl disease. With unwitting human assistance, there have also been other cases in the past of insect larvae causing locust-like devastation.
The damage caused in Taiwan over the past decade or more by the casuarina moth (Lymantria xylina) puts this year's caterpillar swarms in the shade.
Along the coast of central Taiwan, casuarina moth larvae have vigorously "attacked" the coastal windbreak plantations, stripping the beefwood trees (Casuarina equisetifolia) of their green leaves so that they lose their function as windbreaks and their visual attractiveness. Furthermore, the female moths, which are strong flyers, have spread their wings to also threaten central Taiwan's lychee and longan orchards.The Center for Forestry Disease Control
In 1903, the British naturalist Swinhoe first recorded the casuarina moth in Taiwan; by 1928 it was damaging Formosan koa (Acacia confusa) plantations in Miaoli County.
Next, as the beefwood trees which were planted in large numbers during the Japanese occupation began to grow old, they also became hosts for the casuarina moth. Some people even suspect that the casuarina moth was introduced from outside Taiwan, and this is why it is able to do such damage to beefwood plantations.
By comparison, experts regard the caterpillar swarms on school campuses as "minor incidents"; researchers are far more worried about the ecological threat from introduced insect species. All the well-known introduced insect pests are moths.
Since the 19th century, the European gypsy moth (Lymantria dispar) has been one of the biggest headaches for American foresters. European immigrants imported the moth into North America to produce silk, but eventually it escaped from the laboratories, and America's well-developed transport system carried it into every state. It swept across the North American continent, damaging and disfiguring forests, and the poisonous hairs on the caterpillars' bodies also came to be feared as a powerful allergen. In 1981, when the gypsy moth outbreak was at its height, it affected 6 million hectares of forest. Over the past century, various strategies have been tried in the USA, from spraying with all kinds of pesticides to sending out schoolchildren to catch the insects. But the incidence of outbreaks has never been brought under control.
American interest in Taiwan's casuarina moth situation shows how concerned they are by this pest. To prevent the moth entering the US as a "stowaway" on ships from Taichung Harbor, for the last four years the US Department of Agriculture has sent personnel to Taiwan to act as observers and to assist in exterminating casuarina moths.
Taking warning from other countries' experience, Taiwan has set up a Center for Forestry Disease Control to collate reports on forest pests and diseases from all over Taiwan in order to coordinate timely responses. "Only in this way can we get a more in-depth view of problems affecting the whole forestry industry, and reduce their harmful effects to a minimum," says TFRI researcher Chang Jui-chang, who is in charge of the center.Who is encouraging the troublemakers?
In fact, the damage which Lepidoptera larvae cause to forestry pales into insignificance compared with the losses they cause in agriculture, with its much shorter cropping cycles.
The pod borer moth Maruca testulalis, whose larvae feed on pea and bean plants, has long been recognized as a worldwide major pest; and a single moth species, the diamond back moth (Plutella xylostella), whose larvae feed on cruciferous plants (including many leaf vegetables), has caused the Taiwan Agricultural Research Institute (TARI) to invest over two decades' effort into trying to find the most effective ways to control it.
But are caterpillars really so terrible? Compared with other members of the insect world, butterfly and moth larvae are not especially "aggressive," nor are they such rapid breeders and strong flyers as insects from the order Diptera, such as flies and mosquitoes. Most moths and butterflies produce only one new generation per year, and only a minority are likely to attack crops in swarms.
Butterflies in particular have very specific demands as to their environment. They will not breed unless they have adequate space in which to fly and the right amount of sunshine. The females produce only a small number of eggs, and do not lay them all in one place. They are far from being "plague" insects.
In fact, caterpillars' ability to cause damage is amplified by human methods of agricultural and forestry production. Hectare upon hectare of crops and forest plantations may look tidy and pleasing to the eye, but they are also caterpillar heaven. For instance, the Indian cabbage white butterfly (Pieris canidia) is at its most content in cabbage fields, while tropical citrus orchids provide plentiful food for the caterpillars of swallowtail butterflies (family Papilionidae). Many moths are faster breeders than butterflies and less particular about their environment, and amid vast expanses of farmland it would be remarkable if they did not proliferate.
Today's agricultural and forestry production methods aim for the highest possible yields. Over many years, great efforts have been made to control a small number of moth and butterfly "pests" by the use of insecticides. But the insects' resistance to the chemicals has grown, and often one outbreak has hardly receded when another arises. Humans have rarely been able to celebrate victories in their struggle with insects-they have only been able to achieve a "balance of power" by continuing to spray chemicals in order to keep the insects under control.
With reference to the history of the gypsy moth in America, in the book Why Things Bite Back: Technology and the Revenge of Unintended Consequences, author Edward Tenner notes that spraying with pesticides is a threat to biodiversity, but has not been effective in eradicating the gypsy moth. At present the US is going through "alternating periods of crisis and calm" with the moth, with a renewed crisis every few years.
Is there really no solution to the conflicts between humans and insects? Chao Jung-tai, whose research focuses on insect social behavior, suggests that if humans could look at caterpillars from another perspective and accept their "faults," they would no longer need to regard them as obdurate enemies.The only good bug a dead bug?
Caterpillars have their own place in the food chain. Fan Yi-pin, who often collects moth specimens at Fushan in Ilan County, has watched sparrows eating that great enemy of beefwood trees, the casuarina moth. "The sparrows pull off the moths' wings and eat their plump abdomens." Fan's description may sound grisly, but it highlights the moths' indispensable ecological role. Biologist colleagues studying creatures such as frogs, bats or monkeys often ask him to identify the moths these animals feed on.
Chao Jung-tai explains caterpillars' "positive" role: the grubs eat plants, and other animals eat the grubs. They are nutrient converters at the very bottom of the food pyramid, and a source of protein for larger animals. It is estimated that Lepidoptera account for 1% of all wild carnivores' food sources. If butterflies and moths were to suddenly disappear, many animals would find it hard to survive.
By eating plant matter, caterpillars also assist the process of replacement and renewal in the natural environment. The Chinese-language edition of Encyclopedia Americana says plainly: "Ecologically, butterflies and moths are extremely important because their larvae consume large quantities of plant matter, the adult insects transfer pollen when they visit flowers to drink nectar, and they also serve as food for many other animals." Some plants, such as certain orchids and morning glories, rely entirely on specific hawk moth species (family Sphingidae) for their pollination.
The insects which humans regard as "pests" are part of the ecological system. For instance, some ecology researchers believe the gypsy moth is not entirely unbeneficial in the US: on previously cleared land, dominant oak species suppress the growth of other trees, but gypsy moth caterpillars eat oak leaves, thereby giving other trees more of a chance and helping woodland regain its diversity.Object lessons in ecology
When one moves away from the narrow perspective of human economic interest, caterpillars' importance becomes very apparent. Hence experts suggest that caterpillar "swarms" should be dealt with flexibly according to the individual circumstances. Because of agricultural crops' short harvesting cycles, there is as yet little alternative to controlling pest outbreaks by the moderate use of pesticides, unless production methods can be changed; but when transient insect infestations occur in gardens or in woodland-except where "wood borers" such as ghost moths (family Hepialidae) or goat moths (family Cosiidae), which are potentially fatal to trees, are involved-forestry experts generally advise against attempting wholesale eradication with pesticides.
Trees, which have a long growing period, usually reach an eventual "dynamic equilibrium" with insects which both can tolerate. Even casuarina moth caterpillars, which eat beefwood leaves so voraciously, live for less than two months. Although the trees may not be able to function as windbreaks and shade givers during this period, they have plenty of time to recover during the nine months the insects spend as eggs.
In the Kenting National Park on the Hengchun Peninsula at Taiwan's southern tip, about once every five years dense swarms of larvae of the common mormon butterfly (Papilio polytes pasikrates) cover Clausena excavata trees (which belong to the family Rutaceae, the citrus family). There are so many caterpillars that they continually jostle each other off the trees. When NTU entomology professor Yang Ping-shih was asked what should be done about such swarms, he replied that many people never get the chance to see this remarkable sight-it can serve as an excellent aid to teaching ecology.
Occasional caterpillar population explosions in school grounds also present a superb educational opportunity for the children, if they can get over their fear. In Chang Yung-jen's view, such events demonstrate that the power of nature will thwart humans' misguided meddling in natural systems.Desperate avengers
But sadly, due to instinctive fear and a lack of understanding of caterpillars' life cycles, the majority of schools overreact.
When caterpillars infested the five bishopwood trees at Nanliao Elementary School, the grubs were attacked with fire from flame wands and water from hosepipes, and even sprayed with over 100 liters of insecticide.
But this extreme reaction by the school gave the caterpillars an opportunity for revenge. Two-spotted lymantriid moth caterpillars' bodies are covered with fine, spiny hairs, and although the insecticide quickly killed the grubs, their death throes released the hairs from their bodies. The number of poisonous spines drifting in the air increased dramatically, and with the help of Hsinchu's strong winds they got into the children's respiratory tracts; the children also came out in an unbearably itchy red rash. Over half the school's staff and pupils had to seek medical attention.
Yang Ping-shih says that if large trees on school campuses are pruned regularly, the likelihood of caterpillar swarms is reduced, and if lymantriid moths do appear there is no need for spraying-all that is necessary is to keep people away from the trees for the time being. If people understood insects better, they could easily deal with them without needing to resort to drastic measures.
The stream of news reports about caterpillars reflects most people's ignorance about them. Taiwan has probably close to 10,000 species of Lepidoptera, many of which have not even been described. The relatively small number of butterflies among them-around 400 species-are considered aesthetically pleasing, so a fair amount of research has been done on them. But with moths it is a different story: only those which are economically significant "pests" are likely to be studied. However, studying moths purely from the perspective of controlling them has led to a dearth of research into their overall ecology, and this in turn impairs the effectiveness of control measures.Not just a butterfly kingdom
Chao Jung-tai says that biologists in Taiwan lack sufficient knowledge of moths. Without adequate scientific knowledge, even basic identification of moth species is difficult. For instance, an outbreak of the crop-damaging European corn borer (Ostrinia nubilalis) was for a time misidentified as the Asian corn borer (Ostrinia farnacalis).
From an agricultural perspective, there is an even greater need to understand these creatures which compete with humans for food. "The more we know about how they live, the easier it is to deal with them," says Chao Jung-tai--if we understand insects' ecology, natural history and social behavior, we can devise control measures which target their weaknesses.
Studying the ecology of insect populations can also enable humans to predict changes in their density and destructive potential. This allows timely decisions to be made about the choice of control methods, thereby reducing pesticide use and its impact on human health.
Little Taiwan is often called an "insect kingdom," but people here's knowledge about insects is often limited to butterflies-- most know virtually nothing about the other citizens of that kingdom.
Unless people learn more about the other life forms all around them--including little caterpillars--then "sensational" reports about caterpillars defoliating trees are apt to continue to appear in our newspapers.
How remarkable nature is. This summer saw a spate of newspaper reports o f swarms of caterpillars stripping trees bare of their foliage, but the moths which emerge from the chrysalises after the caterpillars pupate are important pollinators which help plants reproduce by transferring pollen between flowers. Pictured here is a hawk moth, which likes to suck nectar from flowers in the cool of dawn or dusk. (courtesy of Yen Sheng-hung)
A podocarp tree covered in inchworms. Caterpillars which gather togetherin such "insect armies" are vulnerable alone, so they seek safety in numbers and try to scare off predators with a show of combined military might. Pesticides sprayed by humans send them scuttling in all directions, but if they enter gardens or houses it is they who are accused of invading people's homes.
Caterpillars ot the two-spotted lymantriid moth. The allergic reactions for which over 500 elementary school pupils and teachers sought medical treatment this summer were caused by their spiny hairs, shown at right at 3000 times magnification. (right: courtesy of Chao Jung-tai)
Because of their subconscious fear of insects, many people's first reaction to caterpillars is to stomp them dead. When a swarm of caterpillarsat Nanliao Elementary School stripped trees bare and gave many children an itchy rash, the school authorities' initial strategy was to attack them with fire and water. But this only spread the allergen all around the schoolyard. (courtesy of Nanliao Elementary School).
Nature lives by its own rules. The pupae in the little white cocoons on this tree trunk have been parasitized by wasps whose larvae have already eaten away their bodies from the inside. The predations of caterpillars' natural enemies limit their numbers as effectively as any family planning campaign.
Large expanses of monocultural crops make easy pickings for insects. Tod ay's production methods depend on holding the "pests" at bay by spraying insecticides. But although humans may be able to maintain a "balance of power" in this way, the bugs can never be eradicated completely.
Do you remember childhood "close encounters" with caterpillars? Today many children take part in organized activities to bone up on ecological knowledge, but they have little opportunity to see moths in their everyday lives.
It may look like a hummingbird, but in fact it's a tiger moth. Many people think moths are only active at night, so those which come out in the day are easily mistaken for something else.
This hawk moth at rest looks like a jet fighter ready for takeoff. Are you interested in getting to know it better, observing it, and even keeping some records to serve as clues to understanding future events in the natural world?