Insect talk

Insects communicate to fulfil their physiological needs as do all living beings on the earth, including humans.

INSECTS can be vociferous and cacophonic. They need to message each other just like any other life form on the earth. But their communication evokes different kinds of responses from humans. At Rishi Valley School, located near Madanapalle (150 kilometres from Bangalore) in Andhra Pradesh, students from the United Kingdom would visit as part of an exchange programme. In 1998, a young boy from London arrived at the school when insect life was in full vigour: courtship calls, new swarms, and the self-destructive attraction to lights were at their peak. He arrived at night and was escorted to a room that everyone thought would catch his fancy; it was surrounded by thick woods and a scenic hill was visible from the balcony. But next morning, we found him groggy, irritable and visibly tired. He had not slept a wink! As a person used only to the sounds of silence in his urban home, the night calls of insects and other animals were a petrifying experience for him; a chirpy set of crickets and katydids chattering non-stop on his balcony added to his woes. As long as he stayed at the valley, he could never look at the insect life without a shudder.

Acoustics is only one of the means of communication in the insect world. Chemical, mechanical, tactile (touch) and visual through mimicry or by emitting lights are the other ways insects share information. In the human world, verbal communication is universal, with everything else being associate means. In the insect world, no one means of communication can be said to be universal or dominant, but the most prevalent, perhaps, is chemical. Of interest are the intriguing non-chemical ways of communication. In terms of structure and process, communication among insects is completely different from what humans are familiar with.

As the young man from the U.K. found out, insects that produce sound can be loud indeed. But imagine his plight if human ears were able to detect all the sounds made by insects! There are many insects that produce sounds in bandwidths that are beyond the detecting capacity of the human ear an adaptation we should all be thankful for. Sounds or calls in the insect world are largely for the purpose of finding mates. When insects produce sounds repeatedly for certain periods of time, they are said to be singing. These nuptial calls, therefore, are persistent and loud. Structures for sound production and reception are quite interesting in the insect world. Sounds are produced in five different ways, and sound-producing and -receiving organs differ in different species.

CICADA

The loudest singers are male cicadas. It is their sound that greets you first in any forest or small wooded area. Some large species can produce sounds exceeding 120 decibels, which at a close range can cause severe pain in the human ear. The sound produced by some of the smaller species is not audible to the human ear but is said to have a nasty effect on animals such as dogs. The next time your dog howls for no apparent reason, he might just be suffering the love calls of the cicada.

This Japanese haiku is to female cicadas, which are always silent.

oshizemi mo naku semi hodo wa iru naramu( as many voiceless cicadasthere cannot be to match thecicadas that are singing )Yamaguchi Seison

The cicada's voice box is a tymbal located at the base of its abdomen. It consists of a pair of ribbed membranes (which are a part of its exoskeleton) attached to muscles. Muscular contractions move the tymbals to help generate the sound. A hollow area in the abdomen acts as an amplifier. These two parts together form the organ responsible for the sounds one cannot miss even if one is hard of hearing. The ear for hearing these sounds is found in both males and females. It is located in the second abdominal segment, and the male cicada often shuts it to prevent damage from its own loud singing. All the songs of cicadas may sound the same to us, but to female cicadas the calls are as different from each other as are the notes produced by the Ventures and Lalgudi Jayaraman.

Tettigonids and gryllids

Comparatively less loud yet quite shrill are the songs of katydids and crickets. The mechanism of sound production is the same in both these insects. According to the biologist Darryl T. Gwynne, a song is more than just an acoustical beacon; it contains information about the quality of the caller that is assessed not only by females or eavesdropping rival males but even by some predators.

The katydids and crickets use their forewings to produce sound by a process called stridulation. This fact was first deciphered by the Chinese in 250 B.C. It also finds mention in the ancient hieroglyphics of Egypt.

One of the veins at the base of the forewing is thick, hard and ridged and acts like a file. The upper surface of the wing is hardened like a scraper. The rest of the wing is thin and papery. When the insect wants to sing for his mate, he raises his wings to pull the file of one wing over the scraper of the other. The sound that is produced gets amplified by the vibrations of the thin papery portions of the wing. This process of rubbing two body parts to produce sound is called stridulation. Katydids, also called bush-crickets or long-horned grasshoppers, belong to the family Tettigonidae and are close cousins of grasshoppers and crickets. Since the insect's call sounds as if it is saying katy-did, katy-did, they were christened katydids.

There are different types of crickets. The nature of calls can vary within each species. The song that attracts the attention of a female changes to a different courtship call when she responds. When the courtship successfully culminates in copulation, the male insect produces a rapturous celebratory song.

According to May R. Berenbaum, head of the Entomology Department at the University of Illinois, crickets of the family Gryllidae are right-winged, that is, they use their right forewing to produce sounds. A cricket's rate of chirping is governed by the ambient temperature. It is in fact possible to calculate the temperature of the environment from a cricket's call.

Mole crickets live underground. They dig tunnels whose openings are shaped like a megaphone. When they sing from inside their burrows, the shape of the tunnel serves to amplify the sound. The ear, which is a tympanic membrane, is present on the tibia the middle part of their leg in crickets and katydids, whereas for grasshoppers and moths, it is present on the abdomen.

There was a European custom that a dead person was not to be left alone until burial. All through the night, one person would stay up with the deceased, a practice referred to as death watch. In the silence of the night, the watchers would hear a spooky tapping sound on the wooden walls or roofs of the house. Those sounds were made by a beetle that infests and resides in tunnels bored in the wood. When it has to attract a mate, it strikes its head against the roof of the tunnel and this is heard as a tapping sound. Thus, the beetle came to be known as the death-watch beetle.

Producing sound by striking a part of the body against a hard surface is seen amongst several insects such as ants, stoneflies, termites and a species of katydid, inspiring Ogden Nash to write:

Some primal termite knocked on woodAnd tasted it, and found it good!And that is why your Cousin MayFell through the parlour floor today.

This description would be incomplete without the inclusion of an insect whose renderings can rob humans of their sleep. When female mosquitoes sing, unappreciated of course by humans, the sound comes from her wingbeats. The male listens to his lady love's songs with his feathery antenna his ear. Nature has endowed insects with organs that can multitask.

luminescence

Long before sailors discovered light signals, insects had mastered the art of signalling to perfection. The firefly and its consort, known to humans by the name glow-worm, practise light talk.

The firefly's flame is something for which science has no name

I can think of nothing eerierThan flying around with an uni5low on a person's posteerier.Ogden Nash

The firefly is a beetle and not a fly. Its light-producing organs are located at the posterior end of the abdomen. Present in this organ are two chemicals, luciferase and luciferin. The enzyme luciferase triggers the process of light production, and luciferin produces the light. The light emission is 100 per cent and is described as cold light because unlike bulbs or tube lights there is no loss of energy in the form of heat. The light produced may be in the form of a glow or flashes.

It is not just the adults that produce light. Even eggs and larvae have the ability to glow. In the world of fireflies, light talk is carried on by varying the duration and intensity of the light signals. The topics for conversation could range from defending territories and warning about predators to the most important one, wooing mates. Signals could be short flashes, long glows or light signals. It is believed that nitric oxide plays a significant role in controlling the nature of a flash. Studies {+1} indicate that the time interval between flashes is a few hundred milliseconds.

In unpolluted habitats, the flashing lights of fireflies at night can be a dramatic sight. This used to be frequent magical sight in my backyard. Today, surrounded by habitat destruction and light pollution, which show no sign of decline, I see an odd firefly now and again wandering aimlessly, stumbling on concrete objects to finally lie hurt, doing the only thing it is instinctively wired to do emit light signals.

When attacked, fireflies shed blood, a chemical so bitter and poisonous that animals do not like eating them. Because of this, there are other insects such as the trilobite beetle and certain flies that mimic the light-producing habit to avoid being predated upon.

Colour display

Colour in the insect world is a passive signal used to scare away predators. Bright red, yellow and black serve to warn predators that the insect so coloured is poisonous and unpalatable, while patterns may convey the information that the insect can sting or cause some other harm. Colourful displays are also used to escape predation. Several moths and butterflies advertise their intent through the presence of large eyespots on the wings. The eyespots can fool a predator into believing that the insect is alert. Some flaunt the eyespots, while others keep them hidden only to reveal them suddenly to startle the predator and escape. Eyespots with fluorescent colours are seen on the caterpillars of several moths.

Birds do not find milkweed butterflies such as tigers and crows tasty since their bodies contain alkaloids derived from the plants they feed on. Several swallowtail butterflies such as gulls and mimes and nymphalids such as the eggflies mimic the colour and pattern of these butterflies to avoid predation. The female of the common mormon butterfly can mimic the body colouration of more than one species of swallowtail butterfly; the choice of colouration is decided by the species that is found in her habitat.

The forewing of many moths appears dull but the brightly coloured hindwing is revealed in a surprise move to escape capture when these moths are attacked. Grasshoppers do the same. The female cabbage butterfly has scales on the dorsal side of its wings that can reflect ultraviolet rays. Brief flashes created by the downstroke of its wings are signals recognised by the male as an invitation for courtship. In certain species of Colias, or the sulphur yellow butterflies, the males have these scales for signalling.

Insect telephones

Research has revealed how insect talk happens via the plant tissue system. The Dutch ecologist Roxina Soler {+2} and her colleagues discovered that flies that chewed the roots of a mustard plant induced the plant to produce a specific type of volatile compound. This chemical travelled through the plant tissues to the stem and leaves. Braconid wasps and cabbage white butterflies can detect this chemical signal and alter their behaviour. Butterflies do not lay eggs on such plants and braconids did not parasitise the caterpillars on this plant to raise their young. The insect below the ground had effectively communicated with those above to stay off the plant. Conversely, leaf-feeding insects transmit similar signals to root-feeding ones using chemicals signals and plant tissues as signal pathways.

When treehoppers wish to warn other hoppers of possible danger, they produce vibrations. These are transmitted through plant tissues to other hoppers present on the plant. Nymphs are known to use this system to attract the attention of their mother.

Social insects

Communication is essential to all insects, but among social insects such as ants, bees, wasps and termites, it is a vital need. In the dark, subterranean interiors of their nests, they relay messages mostly through touch or through chemical secretions called pheromones.

Ants, wasps and bees belong to the order Hymenoptera. These social insects live in colonies, and the queen who starts the colony must organise her workers, soldiers and males to function in a manner that makes the colony flourish. The scientific study of communication amongst these insects dates back to 1880, when the Baron of Avebury, John Lubbock, showed {+3} that ants used odour trails in foraging. Around the same time Father Wassmann, S.J. a distinguished biologist and theologian who worked extensively on ants and wrote a book on intelligence in animals claimed that ants talked to each other through antennal tapping, something similar to the Morse code. Is communication a learnt behaviour or is it instinctive?

When food is discovered, ants lay a pheromone trail on the ground. Other ants smell it using their antennae, and soon a trail is established from the nest to the food source. The movement of more ants on this trail is then brought about through tactile signals. An ant on the trail taps the hindlegs of the ant in front of it with its antenna to inform it that it is following the leader. If the tapping stops, then the leader stops until communication is re-established.

The ants that lay a trail use a suit of pheromones for their communication. Recent research with pharoah's ants, Monomorium pharaonis, showed that the suit contributes to establishing both short- and long-term memory in ants. So the ants can remember the foraging trails as rewarding ones or ones to avoid. Ants thus learn and remember. There is also variety in these chemicals: propaganda pheromones to confuse enemies, alarm pheromones to signal danger, colony-recognition pheromones to detect and evict intruders, caste-specific chemicals for division of labour and certain long-lasting ones to help lost ants find their way back to the colony.

In addition to pheromones, ants use displays, sound and tactile signals to communicate. Tapping on a substrate to share vibrations and direct touching such as antennae to antennae or antennae to legs are examples of tactile talk. Certain ants produce sounds by drumming their abdomen on the substrate, and when more ants join in, a sound, whose volume equals that of human speech is produced. Some ants produce sound by hitting the ground with their mandibles.

When a wider repertoire of messages needs to be communicated, ants use all the forms, that is, display, sound, touch and pheromones, together. No one system of communication is used as a replacement for others. Evolution of multiple signals to communicate is an advantage to help the survival of the colony and an indication of why ants are so successful.

The story of communication would remain incomplete without the inclusion of bees, the legend of the insect world. The classical work done by the ethologist Karl von Frisch in decoding the language of bees won him a Nobel Prize in 1973. That bees communicate has been known since the time of Aristotle, but Frisch found out the details. His elegant experiments showed that dance was the language used by bees to communicate about the location of food sources {+4}.

The nature of the dance signalled qualitative information such as distance, direction and quality of the resource. If a predator was suspected to be present, then bees changed the fervour of their dance. A circular dance indicated the food was close by, but this changed to an eight-shaped tail-wagging dance when the resources were at some distance. In addition to the dance, the bees buzzed, kept silent, danced faster, danced longer or slowed down to add quality to the information.

His experiments showed that bees could use the direction of the sun as a compass. Bees cannot see the sun directly but can see the polarisation pattern of the blue sky. Their ultraviolet vision helps them see the sun through the clouds.

When a new colony has to be started, it is the worker bees that decide the location and not the young queen. Here, too, there are a series of wagging dances that worker bees use to signal to each other to explore and decide the location, and the queen follows. Democracy in the world of bees!

The use of the word language' to describe the communication among bees is not without its detractors. Does it matter? Hugh Raffles, professor in the Department of Anthropology at the New School, New York, says, ...It just points to how our dependence on language has limited our imaginative capacity.

As Sakis Drosopoulos, a professor at the University of Athens, remarks in the book, Insects Sounds and Communication', there is no life without different kinds of sounds. Insects communicate to fulfil their physiological needs as do all living beings on the earth, including humans. Unlike humans, they do not rely merely on sound but take advantage of everything that is available in nature.

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

REFERENCES

1. Barua, Anurup Gohain; Hazarika, Simanta; Saikia, Nayanmoni and Baruah, Gauranga Dhar; Bioluminescence emissions of the firefly'; Nature Precedings: hdl:10101/npre.2007.1351.1. Posted November 19, 2007.

2. Gamorena, Roxina Soler; Plant-mediated multitrophic interactions between aboveground and belowground insects'; PhD thesis; Wageningen University, The Netherlands.

3.Jackson, Duncan E. and Ratnieks, Francis L.W.; Communication in ants'; Current Biology (August 8, 2006), Volume 16; Issue 15; R570-R574.

4. Von Frisch, Karl; Decoding the language of the bee'; Nobel Lecture (December 12, 1973); University of Munich, Federal Republic of Germany.