Insect communication: It’s an art

Scientists have estimated that there are 7-10 million species of insects alive today. As insects evolved into their various species, many forms of insect communication arose: chemical, auditory, visual, and tactile. Insects find all kinds of ways to communicate with each other – even things like music, dance, and theater.

People generally know that crickets chirp and fireflies signal to each other with light, but most people do not grasp the full breadth and complexity of insect communication behaviors. Insects communicate primarily to attract mates, avoid predators, identify individuals of their own species, and find food.

Many insects use auditory signals or “music” to communicate, mainly to attract a mate but also to repel predators and to raise an alarm to other members of its species when predators are close by. Bess beetles, hissing cockroaches, and death-head moths exemplify insects that make noise in order to deter predators.

“Males and females have different wing beat patterns which convey sexuality”

During courtship, insects make sounds to mark territories and to attract mates. For example, male fruit flies sing to females using wing vibrations. “Males and females have different wing beat patterns which convey sexuality,” said Douglass Morse, an entomologist and emeritus professor at Brown. “One of the sexes gives off wing beat patterns that it can’t hear itself but that the other sex can.”

Bombardier beetles make noise by spraying fluid. (photo from skepchik.org)
Bombardier beetles make noise by spraying fluid. (photo from skepchik.org)

When scaring away predators, bombardier beetles, death-head moths, and hissing roaches make sounds the way brass instruments do by ejecting air or fluid from an opening.

Grasshoppers and crickets make sounds by rubbing a row of pegs along the inside leg against the rough surface of its wing, similar to a musical washboard, and beetles rub their wings to make sound in a fashion mechanistically similar to violins.

Cone-headed grasshoppers and crickets also sing in choruses. Two or more individuals of the same species will produce noise at the same time, with their songs at times pulsing synchronously and at other times alternately in order to more effectively attract females.

Insects that use percussive methods to create sounds include damp wood termites, which make sound similar to xylophones by striking a body part against the wood in which they burrow. Cicadas also make their characteristic clicking and screeching sounds by alternately flexing muscles that move two drumlike areas called “tymbals” on either side of their bodies. As the tymbal membrane buckles inward and outward, it creates a clicking sound.

The deathwatch beetle (photo by Leo Reynolds)

Everything from the name to the behavior of the bizarre deathwatch beetle elicits an image of a heavy metal band: the insect literally head-bangs against the walls of its wooden tunnels, making a loud knocking sound to attract mates. The beetle’s name originates from an old superstitious belief that its hair-raising mating call counts down to one’s time of death.

Some insects’ noises actually do foretell imminent death. Certain bees use a method called the “hot defensive bee ball” in which swarms of sometimes hundreds of buzzing bees create so much heat with their vibrations that they cook a predator to death. Bees usually do not resort to this drastic defensive method unless a predator physically encroaches a bee’s space by landing on or sneaking into a hive.

hot defensive bee ball
Honeybees overwhelm a giant hornet by forming a “hot defensive bee ball”

Visual cues are also an important method of communication for insects. The bright, metallic blue coloring of morpho butterflies’ wings distracts predators by reflecting bright light in different directions, making it difficult to focus on the butterfly itself. Eyespots can drive predators away by making the butterfly look like an owl or other large organism, and color patterns help butterflies identify members of their own species.

Bright-colored insects can have a disadvantage when they are trying to hide from predators. In order to conceal the flashy patterns on its upper wing surface, the red admiral butterfly can close its wings and more easily avoid detection by predators.

But while some insects show off their identities with flamboyant patterns and coloration, others attempt to deceive the beholder into believing that the insect is something that it is not. Some insects camouflage themselves with coloration that matches their surrounding, while others masquerade as actual objects, like sticks or leaves. The leaf insect not only looks nearly exactly like a leaf in order to deter insect-eating predators, but it also looks like a dying, browning leaf in order to deter unsuspecting herbivores from nibbling on a decidedly non-vegetarian food source.

 orchid-mantis   leaf_insect  A Praying mantis mimics a flower, left, (photo by Thomas Marent, Minden Pictures/Corbis) and a leaf insect mimics a leaf, right (photo from cals.ncsu.edu)

Other insects try to make themselves look more intimidating than they are, either by displaying threatening body parts or mimicking poisonous organisms. Treehoppers grow elaborate helmets that are sometimes adorned with menacing-looking horns, branch-like formations, and even appendages that make the treehopper look like an ant.

  tree hoppers 4 tree hoppers 3 tree hoppers 2 tree hoppers 1Various treehopper helmets (photos from natgeo.com and nature.com)

Several bizarre species of flies even have near-perfect images of ants on their wings:

  fly with ant pattern on wings ant wings

(photos from pinterest.com)

Mimicry can be used as an aggressive strategy as well. Parasitic Large Blue butterfly caterpillars mimic ant predators so as not to be detected by them when they invade the ant nests and eat their larvae and eggs. Similarly, the death’s head hawk moth mimics the pheromones of bees to enter its hive and steal nectar.

uv vision
Flowers as seen by humans, left, and by bees, center and right (photo from whyflies.org)

Insects pick up signals not only from other insects, but also from the plants from which they collect nectar. Flowers attract bees through bright coloration and distinct smells, sometimes displaying “landing pads” in UV light invisible to people but visible to bees to guide the bee to the nectar at the center of the flower.

We are familiar with a set of senses specific to humans; however, the senses humans use are neither the only senses nor the best; rather they simply differ from other species’ sensory systems based on differing needs and abilities. Insects have highly developed sense of smell or olfaction, which they use for various activities including predator and food detection, sex, aggregation, spacing, trail forming, and alarm. Often, insects place emphasis on olfaction, which is atypical of most other types of organisms, many of which rely heavily on vision and audition. Scientists hypothesize that insects utilize olfaction to such a great extent due to the specificity and lingering nature of the olfactory cues they emit.

Humans can sense chemical cues through smell conveying messages varying in nature from sexual to warning – we can sense each other’s hormones and emotions through pheromones. Insects emit and detect similar signals through olfaction, but are much more sensitive to these cues than humans. For example, the male luna moth has huge antennae loaded with sensory receptors with which it is able to detect a single molecule of female sex pheromones and find a mate.

Parasitic wasps also use olfactory cues to locate caterpillars in which to lay eggs. Dr. Morse, who has studied these wasps for several decades, said, “A parasitized caterpillar will give off a different chemical than one that is not parasitized.” The chemical cue, Dr. Morse said, is “different than one that the caterpillar is generating on its own,” due to the parasitic wasp’s manipulation of the caterpillar.

Hyposoter sp., a parasitoid of cabbage butterflies in action
Parasitic wasp laying eggs in a caterpillar (photo from birdguides.com)

Because chemical signals consist of matter rather than energy, they persist in a particular location over a longer period of time than waves of energy, as with light or sound. Many insects are small, live solitarily, and travel long distances to find food, making it difficult for them to effectively communicate with one another. An insect can trace a physical substance more easily than a visual or auditory signal. In this way, chemical signals left hanging in the air act as a trail of breadcrumbs for the insect to follow towards food, its nest, or a potential mate.

With millions of insect species that are difficult to distinguish even for humans, it can be difficult for a poor-sighted insect to pick one of its own species out of a crowd from miles away. Chemical signals permeate the air in droves. Tracing a path of breadcrumbs through a forest made of breadcrumbs would be impossible if the breadcrumbs weren’t highly distinguishable – and they are, to insects. Chemical signals emitted by females are often species-specific with male counterparts possessing receptors specific to the female’s signals.

Similarly, auditory signals are often highly species-specific. Dr. Morse said, “many insects can hear only at certain restricted wavelengths.” He said he believes mating swarms of midges “are communicating in some way at wavelengths that we can’t perceive.” Many insects separate their songs temporally by singing only during the day or night so that they do not accidentally attract a female of the wrong species.

In these ways, insects avoid clogging the airwaves, or “smell-waves,” with too many signals. Otherwise, insects would be trying to mate across species lines – a doomed enterprise.

Social insects also perform multisensory theatrical displays in order to communicate. “Honeybee dancing is the obvious example, and is really quite remarkable,” Dr. Morse said. Honeybees have evolved highly complex system to visually communicate navigation to food sources through dances. When the honeybee runs in circles, it is indicating the presence of a nectar source in close proximity to the hive. When the food source is farther away, the honeybee runs in a figure eight pattern while waggling its abdomen. The frequency of waggles indicates distance while the angle of the figure eight run indicates the direction of the food source.

Dances are unique for each honeybee species. Dr. Morse said, “You can find other honeybee species in which various parts of this repertoire might be seen, or modifications of it.” He explains that sometimes, bees living in dense forests use olfactory cues more often than dances because dances would not provide successful navigational cues in such a complex environment. In the cases where bees use olfactory cues to lay down a trail, Dr. Morse said, “these patterns are extremely species-specific. There are two species of European bumblebees in which the olfactory cues differ only minutely. The chemicals involved are the same but the molecules differ in one place. In other instances there’s massive common use of similar or identical chemicals but they occur in concentrations that differ from one species to another.”

Other social insects like ants, which have no way of visually communicating food location, lead other ants to food and nest through pheromones. Ants actually combine a sun compass, visual cues, and step counting with chemical signals, but research indicates that ants choose to follow chemical signals over others – in fact, ants have four to five times more odor receptors than most other insects. In one study in which odors normally associated with a nest were moved away from the nest, ants repeatedly moved toward the odors rather than the nest, meaning that the combination of non-chemical signals was not adequate to overpower the importance of the chemical signals in nest location. This makes intuitive sense – if an ant can use a passively detected chemical signal to find its way, it can free up other senses like audition and vision for detecting danger.

Blowflies and cecropia moths also perform a “dance” of sorts by changing their foraging behaviors depending on how good a food source is: if presented with water drops containing varying concentrations of sugar, they will circle an area containing a high-concentration sugar drop, indicating to other insects in the area that the area is rich with a food source, and other insects will join in on the dance.

Insects also also use tactile cues to navigate their surroundings. Many insects use antennae to gather information about their environment and avoid running into obstacles or walking straight into predators lying in wait. Whirligig beetles can sense the ripples generated by movement of other beetles and animals nearby, allowing the whirligigs to avoid running into other members of their own species and detect the presence of nearby predators or prey.

Some treehoppers use tactile clues to warn each other of predators. When a treehopper detects a predator, it produces vibrations in the tissue of its host plant that other treehoppers on the same plant can feel. These kinds of tactile signals are effective communication systems for very small insects that are unable to make noises loud enough to serve as a warning signal.

Clearly, insect behaviors are multifaceted and complex. Insects interact with each other and their surroundings in surprisingly interesting and diverse ways, considering their simplicity as organisms and place on the food chain. We may not think we have much in common with them, but as it turns out, insects sing and dance and do plenty of other crazy, cool things, some of which outstrip human capacities by miles—try beating a leaf insect in a game of hide and seek.

Unfortunately, these diverse and often unique insect behaviors are disappearing. Many described insect species are endangered or on the verge of extinction, and many more undescribed species may go extinct before they are even discovered.

So the next time you see a bug, lean in a little closer and see what wacky wonders you might discover. Resist the impulse to squash it under your boot and think of the amazing things insects do. Let the bug live for one more dance, for one more song. After all, the world could do with a little more dancing and singing.

Advertisements

One thought on “Insect communication: It’s an art

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s