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Volume 28 - Issue 17 :: Aug. 13-26, 2011
INDIA'S NATIONAL MAGAZINE
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NATURAL SCIENCE

Down to earth

TEXT & PHOTOGRAPHS BY GEETHA IYER

Insects' story is one of constant adaptation; among living beings they probably have the best relationship with this planet.

COURTESY: KNECHT ET AL.

THE "TRACE FOSSIL" of Rhyniognatha hirsti.

ABOUT 6,000 fossil records, representing more than 1,260 insect families, have helped reveal spectacular events in insect evolution. Insects are probably the earliest of terrestrial animals to have developed a close association with plants. As plants evolved by adaptive radiation, so did the insects associated with them.

Fossils of insects are not as abundant as those of vertebrates because the soft bodies of insects, once buried, decay rapidly without giving sufficient time for minerals to enter them for fossilisation. So, many insect fossils fall into the category of “trace fossils”.

Fossils of insects are found preserved in amber. From the study of them, we know that insects originated 400 million years ago (MYA), in the Palaeozoic Era, and that by the Carboniferous Period, roughly 350 MYA, there were 11 orders of insects. Of these, only the orders related to modern-day mayflies, dragonflies, cockroaches and hemipteran bugs survived the Permian-Triassic Period (290-200 MYA), when extinctions wiped out nearly 70 per cent of all terrestrial organisms. However, insects as a representative group lived on and utilised this event to adapt and evolve. The fossil 1 of Rhyniognatha hirsti, discovered at the Late Carboniferous Wamsutta Formation of Massachusetts, represents the oldest fossil of winged insects. Studies found that it was closely related to the modern mayfly.


This, then, is the ecological significance of insects: their relationship with the earth, no matter how catastrophic its events, is one of constant adaptation, of changing themselves and their environment and moving into unoccupied niches to survive and prosper. Ecologically, therefore, among living beings insects probably have the best relationship with this planet.

Evolution of mantises and wasps

Mantises (or mantids) and wasps originated in the Permian and Triassic Periods between 300 and 250 MYA. These are fascinating insect species. Having often observed their behaviour, I wonder whether they, like humans, have an “attitude”. Most scientists would pooh-pooh such a suggestion, but when one observes the behaviour of another species, one tends to compare it with one's own.

Mantids

The order Mantodea represents a predatory group of insects comprising approximately 2,400 species that inhabit the warmer regions of the earth. They are abundant in tropical and subtropical areas although several species have now been introduced by humans into temperate regions. Closely related to cockroaches, stick insects and termites, mantises show considerable diversification in morphology, hunting strategy and habitat specialisation. These ferocious insects are active hunters, ambush predators, and sometimes both. Those dwelling on the bark of trees or in deserts are cursorial hunters, chasing down their prey and pouncing upon them. Such species have long, well-developed legs and spines on the first pair of limbs to aid in hunting and capturing prey.



PRAYING MANTISES ARE called so because of their habit of holding their forelegs together in front as if in prayer. Here, an immature mantis.

In many species of mantises, the female does not fly; the male flies at night to prey upon unsuspecting insects attracted to light. Ambush predators lie in wait for their prey, confident of their camouflage. In many ecosystems, they are the largest arthropods and the dominant predators2 . When their densities increase, they can have a profound cascading effect on the food webs of ecosystems as they feed on herbivores, detritivores and other predators. They are commonly called praying mantises owing to their habit of holding their forelegs together in front, as if in prayer. Some people feel, however, that it would be more appropriate to call these insects “preying” mantises in acknowledgment of their hunting skills.

A triangular head capable of 180˚ movement with prominent globose eyes, almost protruding out of the head, makes these insects look quite alien. So well camouflaged are they in their habitat that one may completely miss them as they stay still looking directly at one. Extensive morphological variation has helped them blend with their surroundings. Their features are very strange and yet so attractive to many that they are one of the insects chosen most as pets. Mantis breeding is a hobby in several European countries. The images of praying mantises gives one an idea of how well-adapted they are to remain at the top of the food chain.



THE MUD WASP Rhynchium brunneum builds its nest inside cavities.

Gongylus gongylodes is also called the violin mantis. Unlike other mantis females, the female of this species does not devour the male after mating. This mantis preys on flying insects, its favourite prey being flies, moths, butterflies, and so on. Euantissa pulchra is another interesting mantis. The nymph (a juvenile form) of this mantis could easily be mistaken for an ant of the Camponotus genus and generally hunts alongside its lookalike. Often one finds that not only these mantises but also some species of spiders that look like ants accompany them. This is indeed a statement of the survival success achieved by ants.

Humbertiella, or the bark mantis, blends, as its name suggests, with the bark of a tree. In the ecosystems these mantises inhabit, they generally hunt alongside other arthropods. The Didymocorypha lanceolata is a silver beauty, a sleek and slender mantis that thrives in hot and humid conditions. It is found in India and Sri Lanka. The Schizocephala bicornis, or stick mantis, is so slender that it is often mistaken for the stick insect.

Predators of mantises

Mantises are preyed upon by vertebrates (frogs, lizard and birds) and invertebrates. Of the two, it is easier for a mantis to escape predation by vertebrates. Ants and spiders, too small or too quick to be caught, pose a greater threat to mantises, especially since they hunt in the same habitat. The vast majority of mantises can hear only ultrasound. A single ear made up of two tympana (eardrums), located mid-ventrally in the metathorax, is particularly important for the insects to detect and evade bats at night. Danger also lurks in the form of parasitoids that attack the ootheca (egg case) of mantises. Damage to the ootheca means that a whole new population of mantises will be destroyed, which is a great loss for any species.

Kung fu mantis



The mud wasp Sceliphron madraspatanum builds its nests in human dwellings.

Praying mantises have had a significant impact on human culture. The word “mantis” means prophet or soothsayer. While Zen Buddhism finds in the stillness of a praying mantis a reflection of its article of faith – of action through inaction – martial arts have derived from the hunter mantis a new form of kung fu. Praying mantis kung fu (Tang Lang Chuan) developed in the north of China in the latter part of the Ming dynasty and has two schools of practitioners today. The southern and northern branches of this form differ widely in technique but have one feature in common, namely, that both evolved by observing and studying the mantis.

Around A.D. 1600, a Ming patriot and boxer, Wang Lang, came to stay at the Honan Temple to improve his kung fu. One day, as he was contemplating his skills with disappointment, he chanced upon a praying mantis battling a cicada larger than itself and finally overpowering and feeding on it. Impressed by what he saw, he took the insect back to the temple to study its movements. He amalgamated his existing knowledge with the movements of the mantis and thus created the northern praying mantis style. As with every Chinese form of teaching, the students of this style were encouraged to choose a mantis of their choice and observe it to improve their style. Thus, several styles are practised, but the basic moves remain unchanged. One of them is the use of the mantis hook, where the hand is held to resemble the mantis's forelegs ready to block, parry or strike.



FOUND IN India and Sri Lanka, the Didymocorypha lanceolata is a sleek and slender mantis that thrives in hot humid conditions.

While northern praying mantis kung fu is more popular, southern praying mantis kung fu is more secretive. Developed by the Hakka Chinese, this style adheres closely to the Yin-Yang philosophy and has elements of Lamaistic training. Those who practise this style are supposed to be skilled in using pressure points and meridians for both the Dim Mak (Death Touch technique) and the healing art.



The pompilid wasp. These solitary creatures are commonly known as spider wasps.

Wasps

Ogden Nash, in his poem The Wasp, wrote:

The wasp and all his numerous

family

I look upon as a major calamity.

He throws open his nest with

prodigality,

But I distrust his waspitality.



UNLIKE OTHER MANTIS females, the female of the Gongylus gongylodes does not devour the male after mating. The species is commonly called the wandering violin mantis or ornate mantis or Indian rose mantis.

This, unfortunately, is how we see wasps, as untrustworthy and ready to sting. Folklore has not been kind to wasps either. This significant and remarkable group of insects, along with ants and bees, belongs to the order Hymenoptera. No other insect order has so many species that are not only beneficial to humans but play an ecologically significant role in almost all ecosystems. The generally accepted view is that Hymenopterans made their appearance 250 MYA, in the Triassic Period. The term “wasp” is used by entomologists for insects that come under the suborder Apocrita of Hymenoptera. Modern-day wasps comprise both solitary and social species. The ancestor of solitary wasps was a member of the family Xyelidae (sawflies). However, the evolution of social behaviour in wasps is still a topic of debate.

Many families of wasps are also parasitoids. The evolution of parasitoid behaviour and its ecological significance are of tremendous interest to palaeo-entomologists. This habit seems to have evolved very early in the timeline of insect evolution. A recent find by an Argentinean palaeontologist confirms this. His team found cocoons3 of a parasitoid wasp inside a 70-million-year-old fossilised egg of the largest dinosaur, the Titanosaur sauropod. The evidence of an entire invertebrate community in the eggs of dinosaurs gave rise to the theory that the wasp performed the ecological role of population control by parasitising the invertebrates that lived off the dinosaur egg. The pompilid, scoliid, tiphiid and vespid wasps are some examples of parasitoids that keep a check on several insect and invertebrate communities.



THE NYMPH (JUVENILE form) of the mantis Euantissa pulchra is often mistaken for an ant.

The Sceliphron madraspatanum is a mud wasp that builds its nest among human dwellings. One is currently resident in my home, and for the past five years, she and her children have built several nests and raised several offspring there. Among the myriad places they have chosen as nest sites are chairs, the wooden ceiling, a phone box, assorted door frames and even the television. The wasp that chose the TV was actively discouraged from doing so in the first season, when I went so far as to remove its beautifully built nest. But the next year, it chose the TV again and this time I let it build on. Could one call this adaptation of a kind?



THE STING OF the hornet Vespa tropica can be quite venomous and result in anaphylactic shock.

The wasp built four pitcher-shaped nests and filled them with at least four paralysed spiders and a single egg. The orb, lynx and other species of spiders found in the nests gave me an insight into the spider diversity around the house. Once the egg was laid, the nests were covered collectively with mud so that the construction resembled a mud patch. In nature, this would have been excellent camouflage, but at the edge of television screen, it looked like dirt that ought to be removed. Perhaps, in time to come, the wasp will learn to use man-made materials.



THE SPINES ON the first pair of limbs of the Hierodula membranacea aid in hunting and capturing prey.

Another mud wasp, the Rhynchium brunneum, discovered that the little hole into which the window latch went was a convenient place to rear its young. And so, it first coated the inside with a soft, clay-like soil and then proceeded to stock it up with caterpillars. All the caterpillars it brought were of a single species of butterfly. Soon after bringing in a couple of caterpillars, it laid a single egg and followed this up by bringing in more caterpillars. Finally, it sealed the nest with clay.



(ABOVE AND BELOW) The harmless dauber wasp (Chalybion sp.) uses lime or uric acid from bird faeces to seal its nest.


Throughout the year, the Chalybion is busy scraping the lime off whitewashed walls to use it to seal its nest, which it regularly builds within the sockets of electric switchboards. If one tries to dissuade it, closing all avenues to the switch, it turns its attention to the TV or wooden doors, looking for small nooks in which to rear its brood. Any small cavity is good enough for this wasp, including old nests of potter wasps. It sometimes removes the larvae of Scelipheron wasps and uses that space for raising its own brood. In the process, it seems to keep the population of other wasps under check.

As is evident from this narrative, my home is a haven for local wasps. Yet, not once have I been stung by them. Not while I glared inquisitively at their nests to see the occupants, nor even when I took down the nest from the TV. In my experience, wasps sting largely in response to physical harm. Otherwise, they mind their own business, which, for the most part, is to raise a new brood.



THE STICK MANTIS, or the Schizocephala bicornis, is often mistaken for a stick insect.

So far, I have described solitary wasps: mud daubers, potter wasps and spider-hunting wasps. The vespids are social wasps and hornets that live in colonies. There are about 750 species of paper wasps in the Vespinae family. These social insects live in extraordinarily complex and cohesive societies, where many individuals sacrifice personal reproduction to become helpers in the colony. Life for a social wasp consists of initiation, growth and expansion of its colony. These are architects in the wasp kingdom. When the colony has peaked in size and population, the members disperse and the colony declines.

But only infamy greets paper wasps and hornets. The beauty of the structures they create from the cellulosic contents of plants is lost on humans because they intimidate observers with their numbers and the way they fiercely guard their nests. Unlike potter wasps, they use stings to ward off any creature they perceive as dangerous. The word “hornet” is immediately associated with fear of stings and rightly so for their sting is quite venomous and can even result in death from anaphylactic shock. Paper wasps and hornets can both easily detect moving objects. But if one stays still, they are unable to see one. So if one ever happens to be chased by a hornet or wasp (or even a bee), one only has to remember that stillness is the way to escape from being stung. One must muster the courage to stay still even when they are buzzing near the face; they will soon go away.



THE LARVAE OF tiphiid wasps feed on beetle larvae.

There are several species of paper wasps that are seen both among human habitations and in forests. Species belonging to the genus Polistes and Ropalidia can be seen in many parts of India. If one visits the forests of the Periyar Tiger Reserve in Kerala, one can easily observe the large nests of Ropalidia montana on treetops. Paper wasps build nests of different shapes and sizes.

Social wasps are hunters and scavengers that prey on a variety of arthropod and other animal protein sources. Caterpillars are a favourite food for all wasps. While potter wasps paralyse caterpillars and stock them within their nests, paper wasps cut them down to pieces, chew them well into soft balls of meat and feed them to the larvae. In forests, the Vespa tropica4 often preys upon the nests of the Ropalidia and poaches its pupa. Wasps also need sugar sources to meet the energy needs of general metabolism and flight. Such sources are nectar from flowers, honeydew from aphids or other homopterous insects, and fluids from fruits. In most species, the trophallactic secretions produced by larvae in response to solicitation by adults are used as sugar supplements.



THE BARK-IMITATING MANTIS (Humbertiella sp.) is well camouflaged in its habitat.

A story on wasps would be incomplete without touching on the wasp epic – the story of fig wasps. The fig tree and the fig wasp share a co-evolutionary relationship that spans 80 million years.

There are about 755 fig tree species worldwide, banyan and peepal being two examples. These huge trees are completely at the mercy of a tiny wasp, a few millimetres long, for their propagation and survival. Pollination can occur only through these fig wasps. Conversely, these wasps cannot breed anywhere other than inside figs. Biologists describe this relationship as obligate mutualism. Their story in brief is like this.

A newly emerged female wasp often flies long distances to find another fig (they are believed to be the longest fliers among pollinating insects). Her entry into the fig, which holds the florets within it, is through a small opening called an ostiole. She bores her way using her mandibles and the spines on her legs to reach the florets. In the process, she loses her antennae and wings, but this does not deter her. In the process of reaching the ovary of the fig, she pollinates the fig flowers, after which she lays her eggs in the ovule of some of the florets and dies. When the eggs hatch, the larvae feed on the endosperm of the fig ovary. The newly hatched males and females mate. The male bores a hole through the fig for the females to fly out and the females, laden with pollen from the fig florets, emerge and fly off to find another fig to pollinate. The males die soon after, ei ther inside, or outside if they manage to fly out. Dr Steve Compton, of the University of Leeds, who examined three fossil specimens of fig wasps discovered in the 1920s, said: “[T]he complex relationship that exists today between the fig wasps and their host trees developed more than 34 million years ago and has remained unchanged since then.”

Wasps are so successful that many species of flies, bees and ants mimic them for survival. The significance of this small creature is brought out well by E.M. Forster in his book A Passage to India. He uses the wasp to highlight the spiritual approach of two characters. Critics view the reference to the wasp as Forster's way of saying that no matter how small or insignificant the insect, it and the human being are part of one unified being. This belief, held by many Indians, is spiritual ecology. And if one reflects on this relationship in its totality, one sees that wasps, mantids and humans each have their role to play.

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

REFERENCES

1. Knechta, Richard J., Engel, Michael S. and Benner, Jacob S.; ‘Late Carboniferous paleoichnology reveals the oldest full-body impression of a flying insect'; “PNAS” (2011); 108 (16); pages 6515-6519.

2. Moran, Matthew D.; ‘Praying mantids: Big arthropods producing big effects in food webs'; Department of Biology, Hendrix College, Conway, Arkansas; https://esa.confex.com/esa/2010/ webprogram/Paper46087.html

3. Genise, Jorge F. and Sarzetti, Laura C.; ‘Fossil cocoons associated with a dinosaur egg from Patagonia, Argentina”; “Palaeontology” (2011); Volume; 54, Part 4; pages 815-823; www.palass.org

4. Jeanne, Robert L. and Hunt, James H.; ‘Observations on the social wasp Ropalidia montana from Peninsular India”; “Journal of Biosciences” (March 1992); Volume 17, Number 1; pages 1-14.



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