Pesky pests

Print edition : November 18, 2011

The adult and nymph (right) of the German cockroach (Blattella germanica), one of the four cockroach species that are pests. - PHOTOGRAPHS: GEETHA IYER

Flies, cockroaches and mosquitoes feature high on the list of creatures that humans wish they could banish from the earth.

i will admit that some of the insects do not lead noble lives but is every man s hand to be against them yours for less justice and more charity ?

- Archy and Mehitabel by Don Maquis

ONE of the first questions I am invariably asked is about my attitude towards cockroaches; flies are added as an afterthought. Flies, cockroaches and mosquitoes feature high on the list of creatures that humans wish they could banish from the earth. These three are among the most common images that arise in the mind when one utters the word insect. For eons, they have survived shifting land masses, meteorite hits, climate changes and predatory species, and human assault is just another event insects have adapted to. The proof of this: despite decades of research, we have not been able to eradicate them. We fret and fume and suffer the poisonous concoctions created to kill them, while they remain free, get stronger and continue to enjoy their feast on humans. Is there something that our research has missed altogether? How much do we really know about cockroaches, flies and mosquitoes?

Cockroaches

A common urban myth is that in the event of a nuclear holocaust, the cockroach will be the sole survivor. There is no scientific proof to justify this belief. If one were to go by available research1, then it would seem that only the tiny beetles that infect grain, flour and wood (and about whom we rarely get as bothered as we do about cockroaches) would survive; they would not only do so but reproduce with greater gusto. Cockroaches may be able to withstand higher radiation levels than humans, but they are no match for the aforesaid beetles.

Cucaracha is the root word from which the term cockroach is obtained. This insect belongs to the order Blattodea and made its appearance on earth during the Carboniferous Period (359-299 million years ago (MYA)). The fossil rocks of this period are so rich in cockroach species (about 800 in all) that some palaeontologists have labelled it the Age of the Cockroaches. Although the Carboniferous coal deposits have yielded a large number of fossils, many scientists believe that cockroaches must have evolved much earlier, during the Silurian Period (400 MYA). These fossils, preserved in amber, show parasitic wasps preying on cockroaches, much as they do today. And then, as now, this predation probably kept a check on cockroach populations. This relationship is considered one of the most natural and environment-friendly ways to keep cockroaches under control. In particular, the black wasp called Evania parasites the egg cases effectively, ensuring that no new cockroach is born.

In a dramatic event that unfolds in the darkness of the night, ants prey on live cockroaches. Humans may not be able to vanquish cockroaches, but they are no match for the soldier ants of the Camponotus species. A large swarm of them can take hold of the antennae, legs and wings of a live cockroach and slowly tear it to pieces. No chemicals, no sprays, just the jaws of ants!

THE DOMINO, OR seven-spotted, cockroach (Therea petiveriana) has flagellates and bacteria living symbiotically in its gut helping in digestion.-

Despite their early origin, cockroaches have not undergone much change in overall form and shape. Their dorso-ventrally flattened bodies are capable of occupying a wide variety of niches, especially in the small cracks and holes in human dwellings and in the warm, humid environment of closed kitchen cupboards. They are not too choosy about food either and can live on anything from their shed exoskeletons to motor oil, paper and, of course, the food in our kitchen stores, sinks or drains. Additionally, their life cycle does not require their developing young to search for new habitats or food sources when they hatch.

If there are any underlying principles of long-term survival, surely they are evidenced by roaches....The study of roaches may lack the aesthetic value of bird-watching and the glamour of space flight, but nonetheless it would seem to be one of the more worthwhile of human activities (H.E. Evans2).

There are over 4,000 species of cockroaches. Most of them are found in tropical rainforests. Apart from the four species that are pests, cockroaches show remarkable diversity in size, colour and form. They may be wood-boring; semi-aquatic; commensals in the nests of wasps, ants or termites; desert-dwellers; or, along with bats, cave-dwellers. The curious Madagascar hissing cockroach, sometimes described as a living fossil, is wingless, two to three inches long, and docile. It makes a hissing sound when disturbed. The sound is produced when it expels air from its spiracles (pores on the sides of insects used for breathing). A nocturnal insect in the wild African savannahs, it inhabits decaying logs, performing the ecological role of a scavenger. Since it has no odour and does not bite, it is often kept as a pet in this region.

The seven-spotted cockroach, also known as the desert roach or Indian domino cockroach, is the crepuscular Therea petiveriana commonly seen in southern India. This beautiful species is often mistaken for the aggressive beetle Anthia sexguttata, which it mimics. Also like the beetle, the cockroach inhabits leaf litter in scrub forest habitat.

Although detested by most people, roaches have had their moments of glory. In 1972, a cockroach nearly made it to space on the Apollo 16 space module. It was spotted by an assistant during a routine check for readiness. He reported it, but the roach was never found afterwards. Cockroaches have figured in delightful comedies such as Joe's Apartment where they talk, sing and steal the limelight from the hero. The philosophical musing of Archy the cockroach in Don Marquis' creation The Lives and Times of Archy and Mehitabel is a book lovers' favourite. La Cucaracha is a Spanish folk corrido (a popular narrative song form) that became famous in Mexico during the Mexican revolution of 1910-20. Since this song evolved as an oral tradition, its origin remains unknown. Over the years, La Cucaracha, in its many versions, has become symbolic for many peoples and figures prominently in political satire.

Flies and mosquitoes

The success of insects on this planet has been attributed, among other things, to the development of wings. Evolutionary history records several modifications that wings have undergone in insect groups. The identifying feature of the order Diptera, to which true flies and mosquitoes belong, is that they have only one pair of wings.

Among true flies (as opposed to other insects that have the word fly as a suffix in their names), the hindwings are modified into a club-like structure called halteres, or stabilisers, that have been likened to a gyroscope. Scientific research dating from the 18th century onwards claims them to be necessary for balance during flight. Fossils from the Late Permian (260 MYA) show flies with two pairs of wings. Of the 3,100 fossils of flies from the Mesozoic Era (250-65 MYA), some from the mid-Triassic Period (250-200 MYA) indicate that the hindwings had by then evolved into halteres. During flight, halteres oscillate out of phase with, but at the same frequency as, the wings. And in some cases, they also oscillate when the fly is walking on the ground. Thus, they ensure stability during locomotion. A large body of research3 confirms that they do this by providing feedback on the inertia of the wings, legs and neck muscles.

The biologists David K. Yeats and Brian M. Wiegmann contend that dipterans are the most species-rich, anatomically varied, and ecologically innovative group of organisms. Most people are familiar only with the housefly. However, more than 1,25,000 species of flies have been described by specialists, and several hundreds are waiting to be discovered. Flies come in brilliant colours, sizes and forms and are not always carriers of disease as is commonly believed. In fact, they are very particular about personal hygiene, and if you observe them, you will notice that they clean themselves constantly. Flies are ecologically significant as pollinators, food for vertebrates, scavengers, parasitoids and predators of other insects, bioindicators of water quality and tools for scientific research.

Forensic entomology

Flies help forensic entomologists in medico-legal investigations because of their necrophagous habit as popularised in crime serials on television such as CSI and Bones. Historically, forensic entomology dates back to the 14th century. The first recorded instance of its use can be found in a book titled Washing Away Wrongs by Sung Tzu from China. In the past 30 years, it has been used systematically in criminal investigation. Hermann Reinhard, a German medical doctor, and Jean Pierre Mgnin, an army veterinarian, have contributed to establishing this field. Beetles, moths, wasps, ants and flies are all useful in such investigations. In particular, flies belonging to the families Calliphoridae, Muscidae and Sarcophagidae are helpful in post-mortem analyses.

CRANE FLIES, OFTEN mistaken for mosquitoes, are an important source of food for several vertebrate species such as fish, frogs and birds.-

Flies are often the first to arrive at the site of a dead body as their maggots prefer moist or rotting meat for food. After 72 hours, an estimate of the time of death by traditional means is difficult, and in such cases, entomological information on the life cycle and feeding preferences of flies and other insects is used to reach a conclusion. In the popular television serial Bones, the character Hodgins provides vital entomological information as clues to solving murders.

Blowflies belong to the family Calliphoridae. The word blowfly comes from an old English term flyblown used for meat that has eggs on it. Several blowflies are big, 10-12 millimetres in length, and easily recognised by their bright metallic body colour. They are, therefore, also known as bluebottle flies, greenbottles, and so on. William Shakespeare refers to these flies in plays such as The Tempest and Love's Labour Lost. Blowflies come to dead bodies first because they can smell animal matter from several kilometres away. It is a source of protein for them. They are also pollinators of flowers that have a decaying smell, such as some of the arum lilies. The nectar from these flowers is a carbohydrate source for these flies. Of the 1,100 species of known blowflies, many are common in India.

As their name suggests, flesh flies, which belong to the family Sarcophagidae, breed in dung, decaying material and on carrion. They are medium-sized flies with a grey-and-white chequerboard pattern on their abdomen. They give birth to live young ones on the corpses of animals and humans. They prefer decaying old corpses over newly dead ones, but species differ in their choice of the degree of decay before they feed or breed. This feature along with predictable life-cycle timings are vital clues for forensic analysts.

The common housefly belongs to the family Muscidae, which also has species that are bright and attractive. The Hydrotea sp. of this family is significant for forensic study. These flies feed and breed only on carcasses that are four to five months old or in an advanced state of decay.

Medicine and the fly

The maggots of greenbottles are used in Maggot Debridement Therapy, or MDT, which is the medical use of selected, tested and disinfected larvae of these flies. The maggots do three things: clean out wounds by eating away the dead and infected tissue, kill the bacteria, and stimulate wound healing. This treatment is used very selectively as some species can eat healthy tissue too. Because of this feeding pattern, some species of greenbottle and bluebottle flies can infect animals and cause myiasis. They lay eggs on open wounds of animals, and their larvae begin to feed on the animal's dead and living tissue as they develop. Hygiene is the only way of keeping flies at bay.

(ABOVE AND TOP) Hoverflies, or flower flies, of the family Syrphidae are wonderful mimics and are mistaken for wasps or bees. They are excellent athletes and can hover in the air like birds. They are pollinators and do not sting.-

Ecological importance

With 14,000 species described so far, Tipulidae is among the largest family of the dipterans and are commonly called crane flies. Although found worldwide, they are more common and diverse in the tropics, where they can be seen in shaded areas and in humid and well-wooded habitats. They are rather unique-looking flies with long, slender bodies, legs and wings. In some countries, they are called mosquito eaters. Many adults do not feed at all, are short-lived and die soon after laying eggs. They do not eat mosquitoes, and if they do feed, it is mainly on decaying materials, occasionally nectar, honeydew or pollen. The larvae live for over a year or more in aquatic or semi-aquatic habitats. They play an important ecological role in fresh-water habitats, especially near streams, ponds and flood plains. They break leaf litter into smaller pieces, making feeding easy for those organisms that can take in only small particles of plant matter.

Long-legged flies belong to the family Dolichopodidae. These are small, predatory flies that may be recognised by their long legs on which they stand looking like tiny doll-stools. They have prominent eyes and sport metallic shining bodies. By preying upon small mites, aphids, plant lice, book lice, barklice, thrips and certain midges, they play a regulatory role in containing insect and arthropod populations in agricultural ecosystems.

Another significant group of flies whose adults and larvae serve a similar function are the robber flies of the family Asilidae. They are predators of flying insects, including wasps, bees, dragonflies, grasshoppers and other flies, and are seen in a wide variety of habitats. The larvae of most species live in the soil where they prey on the larvae of other insects too. Commonly known as midges, chironomid flies are bioindicators of water quality. They are very small insects that can be seen close to water sources, paddy cultivations and marshes, and several of them look like and therefore are mistaken for mosquitoes. Some of these adult chironomids do not possess mouth parts and only live for two to three days. Males swarm in large numbers in the evening so that the females can choose a mate swayamvara in chironomids. Swarms are species specific and are dictated by conditions of temperature and wind velocity. Eggs are laid in water or on wet soil. The larvae live in tubes constructed out of the debris found in water. Some larvae are red as they have haemoglobin and are called bloodworms. These bloodworms are food for aquatic animals.

Little fly'

Mosquito is a word derived from the Spanish musketas meaning little fly. Fossils of mosquitoes tell us that they evolved during the Cretaceous Period (145-65 MYA). There are close to 3,000 species of mosquitoes the world over, and they are the best known dipterans. Like the fly, the mosquito has only one pair of wings, which unlike the fly's has scales. They have a feathery antenna, which is put to several uses.

ADULT FLIES OF the family Bibionidae are pollinators. Certain bibionid species fly even when they are mating, which has given rise to the common name love bugs.-

Most mosquito species except the Aedes are crepuscular and feed at dawn and dusk. They mainly feed on nectar for their own survival. But the females need blood, which is their source of protein, for the development of their eggs.

Native American legends abound with descriptions of the origin of the biting mosquito. How mosquitoes came to be is a legend of the indigenous people of the Pacific north-west coast, the Tlingit. According to the legend, there lived a giant in a cave who loved to eat humans, especially their hearts (to the Ojibwe, he was a shape-shifting spirit called the Windigo; in a Japanese folk tale, he was one-eyed hobgoblin). When the worried community gathered to discuss and find a solution, a brave young man came forward with a plan. He fooled the giant, hid in the cave and managed to kill him. The dying giant vowed to return to drink the blood of humans. The young man cut up the body of the giant to pieces and burnt it completely. As he scattered the ashes in the air, each particle of ash turned into a mosquito, and soon the cloud of ashes was replaced by clouds of mosquitoes. He heard the giant's voice echo from the cloud saying, I shall eat you people until the end of time.

Legends of the Tuscarora and Iroquois4 Indians describe a pair of giant mosquitoes that could even hide the sun with their wings and would attack humans and devour them. When these are killed and burnt to ashes, according to the legend, they re-emerge as tiny mosquitoes capable of stinging humans and feeding on their blood.

Ancient cultures wove stories to emphasise the presence and habits of insects and also to record how imperishable they seem. Modern humans invest their energies into scientific research to battle malaria, filariasis, chikungunya and dengue. If mosquitoes cannot be got rid of, what can be done?

THE BROWN CHIRONOMID and (below) the green chironomid. These chironomids may be recognised by their habit of keeping the first pair of legs above their heads. The legs are so long that they stretch well beyond the head. These flies blend very well with their environment.-

Chiang Mai, one of the largest cities in Thailand, is home to an unusual museum the Museum of World Insects and Natural Wonders a significant part of which is dedicated to mosquitoes. Manop Rattanarithikul and his wife, Rampa, set up this museum and are mosquito experts. Manop is referred to as mosquito man. Manop and Rampa, who between them have discovered 18 of the 422 mosquito species of Thailand and published several papers, have this advice to those wanting to avoid getting bitten by the bloodsuckers: They like dark places and breed in nearby water, if you leave a bag outside they will soon collect inside, usually they feed at dusk or dawn. ... Their perspective on these insects is, Mosquitoes are nature's way of naturally transmitting immunity, vaccinating people to resist virus.

The indigenous Algonquin peoples in North America refer to mosquitoes as Sawgimay, meaning little people who bite fiercely and hold that humans should not live on their land. There is wisdom in this statement. Mosquitoes need water to breed. If water accumulation in our neighbourhoods or homes does not bother us or if we wish to continue to occupy or build on marshes and swamps, then we should be prepared to be bitten.

But the last word on these insects is surely Archy's:

insects are not always

going to be bullied by humanity some day they will revolt i am already organising a revolutionary society to be

known as the worms turnverein Certain Maxims of Archy by Don Maquis
Who will be bullied, only time will tell.

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

REFERENCES

1. Berenbaum, May R.; The Earwig's Tail'; The nuclear cockroach; page 96; Harvard University Press, Cambridge (2009).

2. Evans, Mary Alice (editor); The Man Who Loved Wasps'; The Intellectual and Emotional World of the Cockroach by Howard E. Evans; page 53.

3. Thompson, Rhoe A.; Haltere mediated flight stabilisation in diptera: Rate decoupling, sensory encoding, and control realisation'; PhD dissertation, University of Florida (2009).

4. https://www.indianlegend.com /iroquois/iroquois_003.htm

A letter from the Editor


Dear reader,

The COVID-19-induced lockdown and the absolute necessity for human beings to maintain a physical distance from one another in order to contain the pandemic has changed our lives in unimaginable ways. The print medium all over the world is no exception.

As the distribution of printed copies is unlikely to resume any time soon, Frontline will come to you only through the digital platform until the return of normality. The resources needed to keep up the good work that Frontline has been doing for the past 35 years and more are immense. It is a long journey indeed. Readers who have been part of this journey are our source of strength.

Subscribing to the online edition, I am confident, will make it mutually beneficial.

Sincerely,

R. Vijaya Sankar

Editor, Frontline

Support Quality Journalism
This article is closed for comments.
Please Email the Editor