Marvellous forms

The commonly held belief is that insects are dirty and disease-carrying, but most of them are clean and harmless; some even lead sophisticated lives.

THE Dutch ethologist Nikolaas Tinbergen said in his Noble Prize acceptance speech 1 : Many of us have been surprised at the unconventional decision of the Nobel Foundation to award this year's prize for Physiology or Medicine' to three men who had until recently been regarded as mere animal watchers'.... I have decided to discuss today two concrete examples of how the old method of watching and wondering' about behaviour (which incidentally we revived rather than invented) can indeed contribute to the relief of human suffering in particular of suffering caused by stress.

Stress is as natural to human beings as joy. Rather than brooding, watching animals and wondering about them may be a remedy to get rid of stress. Those who indulge in these activities may be looked upon with mild amusement as crazy coots, but watching animals, small or big, can be both therapeutic and enlightening. Insects can be watched with ease as many of them share our dwellings. Contrary to the commonly held belief that insects are dirty and disease-carrying and bite or sting, most of them are clean and harmless some even lead sophisticated lives. And they come in some incredible forms and structures. An insect ... is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble. It can go in for elegant and fantastic forms..., wrote the geneticist and evolutionary biologist J.B.S Haldane in his essay On Being the Right Size. The following are some insects with interesting forms.

LANTERN FLY

A charismatic hopper is the best way of describing the lantern fly, which neither is a fly nor has the ability to emit light. Three features contribute to its charisma unusually elongated extensions from the head; elaborate abdominal plumes, sometimes longer than the body; and the ability to produce wax. The long snout, which is an elongated hollow extension from the head, is a striking feature in many lantern flies. So exaggerated in form are these that a creative explosion of names prevails to describe these bugs, such as peanut-headed bug ( Fulgora laternaria) and dragon-headed bug ( Phrictus quinquepartitus). The purpose served by this snout is still not clear; perhaps protection through mimicry?

The insect's cuticular wax secretions produce a variety of forms such as plumes that extend beyond the abdomen. These waxy tails act as decoys and break off when held, allowing the insect to escape its predators. The eggs, which are laid on a host plant, are also covered with the waxy substance. The larvae that emerge thus have the wax to protect them from nosy predators. Some caterpillars and cockroaches love to eat this wax and spend their time on the back of the lantern fly or close to it. The wax is a permanent feature of all lantern flies, but the snout and plumes are not seen in all species.

These homopteran insects belong to the family Fulgorida and are abundant and diverse in tropical and subtropical regions. This is an ancient family whose evolutionary information is scanty. A broad-winged, moth-like Fulgorid is known to have existed during the Eocene Epoch (56 million years ago, or MYA) in the northern hemisphere. From other sources available, it is believed that some of the elaborate extensions of the head were lost during Fulgorid evolution. The reason why it is called a fly is uncertain, but the prefix lantern has its origin with Madame Merian and her work on the insects of Surinam, published in 1705. She believed that these insects emitted light, a belief that was shared by everyone during her time. The snouts were supposed to emit light when the insects mated; this has since been disproved, but the prefix lantern stayed.

These large, arboreal bugs feed on the sap of plants and excrete a concoction called honeydew comprising excess water and other substances such as carbohydrates, amino acids, hormones and salts. So copious and frequent is the excretion that the insect can drown in it if it is not removed immediately. Several strategies are used to remove the honeydew and avoid predators and fungal contamination. Several animals readily ingest this material for the insect, a relationship known as trophobiosis. Lantern flies eject their secretions forcefully as dew droplets. Because of the force, the droplets fall far away from the insect's dwelling, sometimes even a metre away. But a species of snail, a species of cockroach and a few moth species have found a way to intercept this secretion and feed on it 2.

There are multiple species of bacteria in the lantern fly's digestive system that provide it with the essential nutrients not available from its own plant-sap diet. As lantern flies are colourful, they are often mistaken for butterflies. Along with planthoppers of the Membracid family, they constitute bugs that have strange shapes and forms, an inspiration for cartoonists, moviemakers and storytellers.

LACEWING

The ability to avoid detection, or crypsis, is an effective defence used by insects to guard against potential predators. For insects, mimesis is an effective method of plant mimicry to escape predation. The stick insect and the leaf insect have perfected this. Although this feature is not seen in today's lacewings, the discovery 3 of two extraordinary fossils from China belonging to the Middle Jurassic Period, 165 MYA, shows a very specific form of mimesis called pinnate leaf mimesis. The significance of this find lies in the fact that flowering plants with pinnate leaves as seen today were absent at that period. It is also evidence of the existence of a greater diversity of insect forms in those times. These gentle, winged insects evolved in the early Permian and gradually underwent changes in these millions of years to what they are now.

Lacewings belong to the family Chrysopidae of the order Neuroptera (which means net-winged). They remain hidden under vegetation for most of the day and become active at night and during dawn and dusk. If threatened, they pretend to be dead or release a bad odour to discourage predators. Some species feed exclusively on nectar and pollen. Others, in addition, are predaceous on arthropods, such as mites and aphids. The larvae feed on a variety of insect pests such as aphids and mealybugs, and this earned them the pet name of aphidlions. Both the larvae and the adult are ideal for the biological control of pests.

The wings of Chrysopids are large, transparent and criss-crossed with veins hence the name lacewing and held roof-like over the body. Soft lace-like wings, shining eyes and a gentle hue of green or brown make them attractive. The ears present on the wings help them detect ultrasonic sound waves and avoid predation by insectivorous bats. If bats detect them, they perform a series of acrobatic, aerial manoeuvres 4 to avoid being caught. They are also capable of releasing sounds imitating bat cries to protect themselves from being caught by bats.

Male and female green lacewings sing duets. To produce this sound they have to dance. Research by evolutionary biologists at Yale indicates that there is a low-frequency courtship song that precedes mating. This is done by vibrating the body without touching the ground. The male sings to attract the female, and if she likes him, she joins the dance to sing with him. The divergence in the courtship song may be a reason for the evolution of new species.

Lacewing eggs are laid in such a way that they hang from the underside of leaves by thin stalks, close to mealybugs or aphids. The larvae climb up the stalk to the leaf to feed; they are voracious predators and start eating immediately. In two to three weeks they spin themselves into silky pupae from which the adults emerge after a week. The average lifespan could be about four to six weeks. However, this is only a generalisation, and specific species may show different durations in their life history.

STONE FLY

The stone fly belongs to the order Plecoptera and to one of the most primitive groups of insects, with its earliest relatives dating back to the early Permian Period, nearly 300 MYA. Stone fly ancestors are believed to be among the earliest insects to fly; hence, they are used as a model for understanding and studying the evolution of flight in insects. Modern-day stone flies are weak fliers. Their wings are as beautifully veined as the lacewing's, but unlike the lacewing, these insects keep their wings folded flat on the back. Some species do not possess wings. Long antennae, sometimes longer than the body, and long abdominal cerci (thread-like extensions from the last abdominal segment) are features to identify this insect.

An angler's dream bait, stone flies are aquatic insects whose nymphs need moving water for development. They can be seen resting on vegetation or rocks but always close to streams. They are more common near forest streams than among urban dwellings. Since they can survive only in well-aerated water and the slightest pollution in water can harm them, they are bio-indicators of water quality. These insects and their nymphs are natural food for trout and other fish.

Like the lacewing, male and female stone flies locate each other through a series of body drummings. A male taps its abdomen on the ground and the female picks up this vibration and responds. This continues until they meet each other. The beats vary from species to species.

The females lay the eggs in a ball-like structure that they carry on the abdomen and from which they release the eggs in water. This they do by flying close to the surface of the water and dipping their abdomen into it. All the eggs are not released at once, and the female repeats this process a few times until all eggs have been safely deposited. This process is quite dangerous for a weak flier. Sometimes, in this process of egg deposition, the insect can become a meal for a waiting fish.

While the eggs may hatch in three weeks' time, it can take up to three years for the nymph to become an adult. Under unfavourable conditions, physiological mechanisms delay the hatching of eggs. When the nymph is ready to emerge as an adult, it crawls out of the water and sheds its larval exoskeleton. Sometimes adult stone flies do not feed at all but remain alive for a few weeks during which time they mate and lay eggs. A large part of their life is spent as a naid, or nymph. These nymphs stay at the bottom of the river, a fact well known to the fish that feed on them.

STICK INSECT

Like the Phantom of the comic book, stick insects, or phasmids, can be called the ghost who walks. This insect is a perfect example of camouflage. Stick insects belong to the order Phasmatodea; the name derives from the Greek word phasma meaning apparition or phantom. The stick insect's demeanour, its measured slow gait, and its ability to stay still on the twig of a tree justify the name. Brown or green, long and cylindrical, they are extremely difficult to spot for they mimic the vegetative parts of a tree to near perfection. They are also the longest among insects, with the female of the Phobaeticus sp. reaching more than 50 centimetres in length. Like lantern bugs, this insect too is abundant in tropical regions.

The adult insects are nocturnal, but the nymphs are diurnal. The males are smaller than the females. It is the males that have wings, while the females are wingless. In many species both the sexes are wingless. The nymphs can regenerate lost legs or antenna during the time of moulting. They are herbivorous and can defoliate trees and shrubs. Some scientists consider this ecologically significant for forest ecosystems.

The insect adopts a variety of defence strategies to avoid capture or predation. It can change colour to camouflage itself, feign death, assume grotesque or asymmetrical postures, sway gently to mimic a branch in the wind and, in extreme cases, inflict pain using the spines on its forelegs. Some winged species startle the predator by displaying their coloured wings before disappearing into the undergrowth. Even the nymphs twist and turn their bodies to look like an ant or a scorpion in order to avoid predation.

Stick insects are capable of releasing pungent-smelling secretions to keep predators away. They can also vomit their stomach contents or bleed haemolymph from the joints of their legs or exoskeleton when harassed and escape predation as these secretions are unpalatable.

Mating happens over a prolonged period, and the species Necroscia sparaxes, which is found in India, has been observed to have remained coupled for 79 days at a time. While sexual reproduction is common, many phasmids reproduce parthenogenetically. Eggs are laid in a variety of places and take an average of 20 days to hatch. At first, the larva looks like an ant and immediately takes refuge in a tree. It takes several months and moults to reach adulthood. Diapause (delayed development) is common in some temperate species. The Indian stick insect, Carausius morosus, is a favourite among those who keep insects as pets.

EARWIG

The 2,000 species of earwigs worldwide belong to the single order Dermaptera. Recent research traces the oldest Dermaptera to the Late Triassic/Early Jurassic Period. The earliest fossil records of earwigs indicate that they share a common ancestor with modern-day cockroaches. Fossils that surfaced from the Jurassic Period (208 MYA) show features similar to modern earwigs.

The earwig's claim to fame or infamy lies in the mistaken notion that it likes to crawl into human ears to stay put or lay eggs inside the brain. The entomologist May Berenbaum, who researched the subject, confirmed that there was no record of this habit in 10 centuries of literature 5.

How these insects got this reputation is a mystery. If they have ever been found in human ears, it would be just as accidental as finding any other insect in there. In fact, earwigs inhabit dark, moist places during the day and come out during the night to feed. Most of them can be found in crevices or leaf litter and underneath stones, bark and fallen logs. Earwigs are omnivores, scavengers or herbivores. Although predominantly free-living, a few are commensals or parasites of bats, and some are semi-parasites of rodents.

The role of earwigs in the horticultural field in the biological control of pests is worthy of exploration as many of them feed on caterpillars and hemipteran bugs. Their other favourite foods include soft and tiny insects, cockroach nymphs and flies. If one finds earwigs inside one's home, it is most likely because of decomposing organic waste that has been left around. Pathogens and insectivorous birds such as treepies and hoopoes keep a check on the earwig population.

Free-living earwigs are easily recognised by their characteristic forceps-like paired and curved cerci at the end of their abdomen, because of which they have acquired names such as pincer bugs, or scientifically, Forficula (Latin for shearing). The cerci, more curved in males than in females, are used for defence, to capture prey or to fold their wings. Small (4-50 millimetres) and blackish brown in colour, this insect has a flattened body with its wings folded over, which makes it easy for it to crawl into crevices.

The forewing is short and hard as in beetles and protects the membranous hindwings, which are semicircular and fan/ear-shaped (probably why they are called earwigs). The folding and unfolding of the hindwings is an intricate and complicated process involving the use of cerci. This may be why earwigs do not resort much to flight. The parasitic species are entirely wingless.

An unanswered question for science is the presence of a spare penis in the male earwigs of the family Anisolabididae. The females have only one genital opening; hence, the function of this organ is an enigma.

Female earwigs are excellent mothers who take full care of their broods. They make a nest by burrowing in suitable spaces such as under a pile of leaf litter or a rock and deposit their eggs in it. They remain in the burrow protecting the eggs from predation or destruction, and also from fungi, by continuously cleaning them. When the eggs hatch, the larvae first feed on the egg casing and then on food regurgitated by their mother. She leaves the nest after the second moult of the young ones, when they have become nymphs and can take care of themselves. Do you still think earwigs need the human ear?

OTHER FORMS

Like adult insects, insect larvae are masters of deceit. The nymph of the froghopper secretes a bubbly nest that looks like human spit. The larva of a tortoise shell beetle looks like a piece of faeces; it carries its faecal matter and dried leaves on its back for camouflage. These insects do not emit any foul smell.

There is never a dull moment if one chooses to watch insects. When shall we have an entomological laboratory for the study not of the dead insect, steeped in alcohol, but of the living insect... the instinct, the habits, the manner of living, the work, the struggles, the propagation of that little world with which agriculture and philosophy have most seriously to reckon? asked the French entomologist Jean Henri Fabre.

No microscopes, no granite tables, no Bunsen burners, no laboratory manuals are required; a little time, lots of patience and an open mind can lead one to the laboratory where one can watch and wonder.

Geetha Iyer is an author, a nature enthusiast and an independent consultant in the fields of environment and education.

REFERENCES

1. Tinbergen, Nikolaas; Department of Zoology, University of Oxford, England; Ethology and Stress Diseases', Nobel Lecture, December 12, 1973.

2. Naskrecki, Piotr and Nishida, Kenji; Novel trophobiotic interactions in lantern bugs (Insecta: Auchenorrhyncha: Fulgoridae)'; Journal of Natural History (2007); Volume 41; (37-40); pages 2397-2402.

3. Wang, Yongjie; Liu, Zhiqi; Wang, Xin; Shiha, Chungkun; Zhao, Yunyun; Engel, Michael S. and Ren, Dong; Ancient pinnate leaf mimesis among lacewings'; PNAS (September 2010); Volume 107; www.pnas.org/cgi/doi/10.1073/pnas.1006460107

4. Miller, L.A.; Physiological responses of green lacewings (Chrysopa, Neuroptera) to ultrasound', Journal of Insect Physiology (1971); Volume 17; pages 491-506.

5. Berenbaum, May; The Earwig's Tail: A Modern Bestiary of Multi-legged legends'; Harvard University Press (2009); page 12.

6. Photograph of nesting earwig: Creative Commons Attribution-Share Alike 3.0 Unported. https://creativecommons.org/licenses/by-sa/3.0/deed.en