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.
[Picture Caption]
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?