What Is An Insect?

Why are Insects so Successful?

Throughout history, insects have been able to adapt and thrive in various environments. They have a high reproductive rate, with some species capable of producing hundreds or even thousands of offspring. 

Their success can also be attributed to their versatile diet and ability to eat plants, other insects, and even decaying matter.

In addition, insects have a hard exoskeleton that acts as a protective shield and supports their bodies. This allows them to survive harsh conditions and adapt to changing environments

What is an Insect?

An insect is described as an air-breathing animal with a hard-jointed exoskeleton and (in the adult) a body divided into three parts:

• The insect head with one pair of antennae.
• The insect thorax carries three pairs of legs and usually two pairs of wings.
• The insect abdomen contains the guts and reproductive organs.

Insect Habitats. Distribution and abundance

Where they live

Well, everywhere on land, anyway. Very few insects have colonized the sea.

Though some, like the Marine Flies (Halobates sp.) and the Seashore Collembolan, Anurida Maritima, live on the surface of it. Also, the larva of a small number of True Flies (Diptera) and Beetles (Coleoptera) have a habitat beneath the surface, mostly in rockpools.

On the land, however, there isn’t anywhere you can go that you can’t find some insects. Even in the frozen extremes of Arctica and Antarctica, you’ll find some insects alive and active during the warmer months.

You will find that insects are literally ubiquitous…

They are in the soil beneath your feet, in the air above your head, and on (and in) the bodies of the plants and animals around you. Oh, and as well as on and in you.

Some of the most adventurous insects you can find living in the strangest of places, like in Mono Lake, California, which is nearly as salty as the Dead Sea, in pools of crude oil, and also in the hot springs of Iceland.

How many insects species

The incredible number of insect species is only dwarfed by the incredible number they sometimes occur in.

In 1943, Professor Salt found that an acre of British pastureland near Cambridge supported over 1,000,000,000 Arthropods. Of which, nearly 400,000,000 were Insects, and 666,000,000 were Mites. The remaining 38,000,000 were Myriapods (Centipedes and Millipedes).

Population regulation

The insect population is regulated through natural factors and human intervention.

Natural factors such as predation, disease, and competition for resources play a role in controlling insect populations. 

Humans also play a role in regulating insect populations through the use of pesticides, introducing natural predators, and habitat management. 

It is important to carefully monitor and manage insect populations as they can cause harm to crops, spread disease, and affect the overall balance of an ecosystem. 

While some insect populations may need to be controlled, it is also important to consider the potential impact on non-target species and the environment.

Appearance and Anatomy

A fuller description of the various bits that make up an insect can be found on the Insect Anatomy page.

Sizes

There are several different ways of measuring the size of an insect.

The Largest Insect

Most people would consider the largest insect to be the bulkiest. In this case, the champion insect is the Acteon Beetle (Megasoma acteon) from South America. The males of which can be 9 cm long, 5 cm wide, and 4 cm thick.

However, there is a serious challenge for the heaviest insect in the world, in the form of the True Wetas from New Zealand. For instance, a gravid female Deinacrida heteracantha can weigh as much as 70 grams.

Another competitor for the title of largest insect is the weird insect South American Longhorn Beetle Titanus giganteus.

These giants can have a body length (not including antennae) of over 16 cm (6.5 in). Other longhorn beetles are nearly as large and may look even bigger because of their long legs, i.e. Xixuthrus heros from Fiji.

The Smallest Insect

There are many very small insects, far more than there are giants.

Many beetles are, in fact, less than one millimeter in length.

The North American Feather winged Beetle Nanosella fungi, at 0.25mm, is a serious contender for the title of smallest insect in the world.

There are also many small Hymenoptera, especially in the Superfamily Chalcidoidea. These include the Fairy Flies (of the family Myrmaridae), of which Alaptus magnanimus at 0.21mm long, was once thought to be the smallest insect in the world. 

However, another Hymenopteran parasite now holds the record.

Other insect orders with extremely small members are the Diptera (True Flies) and the Collembola (Springtails).

External morphology

Cuticle

An insect’s outer skeleton, or cuticle, is made of chitin and proteins. This protective layer helps the insect maintain water balance and defend against predators and environmental stressors. The cuticle may also have sensory functions, such as detecting touch or vibrations.

Depending on the insect species, the cuticle may be smooth or have protective spines, bristles, or scales. Certain insects, such as butterflies and moths, also have specialized pigment-containing cells in their cuticle called ommatidia, which give them colorful patterns for camouflage or mating displays.

Head

The eyes, mouthparts, and antennae can all be found on an insect’s head. Many insects have compound eyes, composed of numerous small visual units called ommatidia. These provide a wide field of vision and the ability to detect movement quickly.

Insects also have various mouthparts for feeding, including chewing, sucking, and piercing-sucking. The antennae, located on the forehead, serve as sensory organs for touch and smell.

Thorax

The thorax is the middle section of an insect’s body and comprises three segments: the prothorax, the mesothorax, and the metathorax. Each segment has a pair of jointed legs, allowing insects to walk, jump, and fly.

The thorax also houses the insect’s flight muscles and legs.  Many insects have several pairs of legs, ranging from four to six. The legs are adapted for different functions, such as digging, jumping, or grasping prey. Some insects also have wings attached to the thorax, allowing them to fly.

These wings may be membranous and flexible, like in dragonflies, or hard and protective, like in beetles. In some species, only the male has wings, while in others, both sexes are capable of flight.

Abdomen

The abdomen is the hind section of an insect’s body and contains vital organs such as the digestive system, reproductive system, and nervous system. 

The abdomen also houses structures for producing silk or defensive chemicals, as well as external reproductive structures in males. 

 

For insects such as bees, the abdomen also contains the “stinger” or ovipositor, used for defense or laying eggs. Some insects, such as caterpillars, have fleshy appendages called prolegs on their abdomen for grasping and locomotion.

Internal morphology

Digestive system

Insects have a digestive system responsible for breaking down food and extracting nutrients. However, insects also have a specialized region called the crop, where they can store food before it enters the rest of their digestive tract. Bees, for example, use the crop to store nectar to bring back to their hive. 

Their digestive system also includes salivary glands, which secrete enzymes to break down food, and a rectal

 chamber for waste disposal. Regarding excretion, insects have several specialized cells called Malpighian tubules that help remove waste from the blood and release it as urine.

Some insects, like termites and certain beetle species, have adaptations that allow them to break down cellulose from plant material. This is accomplished through symbiotic relationships with microorganisms in their digestive tract that produce enzymes capable of breaking down the tough substance.

Circulatory system

Insects do not have a traditional circulatory system, with a heart pumping blood throughout the body. Instead, they have an open circulatory system where hemolymph, the insect equivalent of blood, is pumped through the body cavity and into organs.

Some insects, such as dragonflies and bees, have a dorsal heart that pumps hemolymph through the body. Other insects, like cockroaches, have several small tubular hearts along their abdomen that pump hemolymph to different body parts.

Respiratory system

Insects also have a unique respiratory system consisting of tiny openings called spiracles located along the sides of their body. These spiracles lead to air tubes called tracheae, which deliver oxygen to tissues and remove carbon dioxide waste. 

As insects lack lungs, gas exchange occurs directly at the tissues through diffusion. Some insects, like beetles, also have adaptations such as special muscles that can open and close their spiracles to regulate gas exchange.

The respiratory system in insects also plays a role in sound production, as some insects, like crickets and cicadas, use their spiracles to vibrate and create noises. These noises are used for communication and mating calls.

Reproductive system

While the specifics vary between male and female insects, both have reproductive organs responsible for producing and transferring gametes.

In males, this includes testes that produce sperm and external genitalia for mating and fertilization. In females, the ovaries produce eggs, and there is internal genitalia for receiving sperm and laying eggs.

Certain insects, such as honeybees, also have a special organ called the spermatheca, which can store sperm for the later fertilization of eggs. In honeybees, the queen bee will mate with multiple male drones and use stored sperm to control the genetics of her offspring.

Another unique adaptation in insect reproduction is the process of parthenogenesis, where females can produce offspring without male fertilization. This adaptation is seen in insects such as aphids, allowing for rapid population growth and survival in harsh environments. 

Nervous system

You’d be surprised to find that insects have a fairly advanced nervous system, consisting of a brain and nerve cords running along the body. Their brain is responsible for coordinating sensory information and controlling behavior and movement.

Related article: The 10 Smartest Insects In The World

The nervous system also includes a network of sensory receptors, allowing insects to detect stimuli such as touch, taste, smell, and sound. Some insects also have specialized sensors for detecting things like temperature and magnetic fields.

Insects such as bees and ants also have a sophisticated social system, with advanced communication and division of labor. This is made possible through their complex nervous system that allows for learning and information sharing within the colony.

Insects locomotion

Flight

Many insects are able to fly using their wings. This allows them to quickly escape predators and find food or mates. Some examples of flying insects include butterflies, bees,  and moths. Wings not only work as a mode of transportation but can also be used for communication and courtship displays.

Depending on the insect, the flight may be continuous or intermittent. Continuous fliers, such as dragonflies, constantly beat their wings to stay airborne. Intermittent fliers, like bees, alternate between flapping and gliding.

Wings are not the only way insects can fly. Some species, such as aphids and leafhoppers, have special structures called halteres that allow them to maneuver in the air. Others, like ants, use gas produced by their own bodies to float through the air.

Walking

While some insects fly, others use their six legs to walk on land. This allows them to search for food and mates, as well as evade predators. Walking is often the primary mode of transportation for beetles, cockroaches, and ants.

Insects have adapted specialized structures on their feet called pulvilli, which help them stick to surfaces and climb vertical surfaces like tree trunks or walls. Some species, such as spiders, also use silk to create webs or lines for walking on.

Swimming

Some insects, such as water striders, live and move mainly in water. They have hydrophobic hairs on their legs that allow them to glide over the surface of a body of water effortlessly. Other aquatic insects, like backswimmers and diving beetles, use their legs for paddling underwater.

Not all insects are able to swim, but many have adaptations that allow them to survive in water. Water boatmen, for example, trap air bubbles under their abdomen to increase their buoyancy and breathe underwater.

Senses & Communication

Eyes and vision

You’d be surprised as to how well insects see. Many have compound eyes made up of thousands of individual lenses, allowing them to detect movement and see in all directions simultaneously. An example of such an insect is houseflies, which can see in color and even perceive polarized light. 

Other species even have a 3D vision, like the praying mantises. They use their vision to hunt for prey. If you’ve ever seen a praying mantis catch and eat a fly, you know how precise its vision is. 

Ants also have excellent eyesight, using it to navigate and communicate with each other. They use visual cues from the sun to find their way back to the nest and can even recognize individual colony members through visual identification. 

Touch 

While not as sensitive as our own sense of touch, insects use hairs on their body, called sensilla, to detect vibrations and changes in temperature. This helps them navigate their surroundings and communicate with each other.

Insect sensilla are divided into four categories: olfactory, mechanosensory, gustatory, and those hygro- and thermoreceptors. In ants, sensilla on their antennae are used to transmit tactile information and help them communicate with each other through touch.

While many insects have sensilla on their antennae, others have them on various parts of their body, like the legs and wings. One example is the honeybee, which uses sensilla on its legs to detect and collect pollen.

The sense of touch is also important for mating. Many male insects tap or vibrate a female’s body to signal their interest and initiate copulation. Insects such as moths use sensilla on their antennae to detect the pheromones released by potential mates.

Insects, according to entomologists, do not have pain receptors as vertebrates do. They don’t feel ‘pain,’ but they may feel certain irritation and can probably tell if they’re hurt.

Sound and hearing

Many insects communicate through sound, either by stridulation (rubbing body parts together to make noise) or tymbalation (vibrating specialized organs to produce sound).

Crickets and grasshoppers are well-known for their ability to stridulate, using their wings to create chirping sounds. Each species has its own unique call, allowing them to attract mates and warn other individuals of potential danger.

Other insects, like cicadas and some species of beetles, use tymbal organs located on their abdomens to make loud buzzing or clicking sounds. These noises can be heard from a distance, attracting mates or warning off predators.

Some insects, like the parasitoid wasp, have ears located on their antennae or thorax and are able to hear and respond to specific frequencies. These insects use sound as a way to locate hosts (typically other insects) for their offspring to feed on.

Each insect species has its own unique way of communicating through sound, allowing them to survive and thrive in its environments.

Chemicals

Not all insects rely on sound to communicate. Many species, like ants, bees, and termites, use pheromones to transmit information.

Pheromones are chemicals released by an individual that can elicit a response from other individuals of the same species. In ants, for example, specific pheromones are used to mark trails to food or attract mates. Pheromones can also be used as alarm signals, warning others of danger.

In addition to pheromones, insects use chemicals to find food and identify potential mates. Butterflies, for example, have taste receptors on their feet that allow them to taste the nectar of flowers while they’re landing on them.

Chemicals also play a role in insect defense mechanisms. Beetles, like the bombardier beetle, can mix and release chemicals to create a hot, noxious spray to ward off predators.

Insect aggregation is another defense mechanism. These insects have some form of chemical defense against predation and are usually brightly colored.

Instincts

If you’ve seen a spider spin its web or a bird build a nest, you may think that these intricate tasks require some level of learning and experience. However, for many insects, these behaviors are instinctual and hardwired into their biology.

Insects can also instinctively recognize members of their own species, as well as potential mates and enemies. These instincts, passed down through generations, ensure their survival and reproduction in the wild.

light production and communication

Fireflies and certain species of beetles are able to produce light through a chemical reaction in specialized organs called photophores. This bioluminescence can be used as a means of communication, attracting mates, or warning off predators.

In some cases, the production of light is linked to sexual selection. Male fireflies will flash specific patterns to attract females. When a female sees a male with the desired pattern, she will flash back to signal her interest.

Other insects, like click beetles, use their bioluminescent abilities as a defense mechanism. When threatened, they are able to startle predators by producing sudden flashes of light.

Classification & Taxonomy

All these species are divided up into about 32 orders (depending on whose taxonomic system you use) of which the largest is the Beetles or Coleoptera.

Related article: The 12 Ugliest And Creepiest Bugs In The World

They are an incredibly diverse group of animals with 125 different families and around 500,000 species.

What are the different types of insects?

The insect species are highly diverse and abundant in nature. Insects can be classified into a few main groups: beetles, cockroaches, butterflies and moths, bees, wasps and ants, true bugs, flies, grasshoppers, and crickets. Other smaller groups include dragonflies, cicadas, and stick and leaf insects. 

Arthropoda is a larger group that includes all animals with segmented legs, bodies, and exoskeletons. Insects belong to it. Entomology books primarily study four classes:

• Class Hexapoda or Insecta (Insects)
• Class Arachnida – (spiders, ticks, mites, scorpions, and relatives).
• Class Diplopoda (millipedes)
• Class Chilopoda (centipedes)

The insect orders currently stand at 27. Three other orders that were once considered insects, the Entognatha, are part of the Hexapoda but not recognized as true insects. 

The animals that most people consider insects are united in the term Hexapoda and comprise five distinct groupings, superorders, or sub-classes (depending on who you ask).

The Orders

Sub-Class	Order
Apterygota	Archaeognatha or Microcoryphia Zygentoma
Palaeoptera	Ephemeroptera Odonata
Polyneoptera	Orthoptera Phasmida Plecoptera Dermaptera Dictyoptera Embioptera Grylloblattaria Mantophasmatodea Zoraptera
Paraneoptera	Hemiptera Phthiraptera Psocoptera Thysanoptera
Endopterygota	Coleoptera Diptera Hymenoptera Lepidoptera Mecoptera Megaloptera Neuroptera Siphonaptera Raphidioptera Strepsiptera Trichoptera

Life cycle

Metamorphosis

Metamorphosis is the transformation that occurs as the insect develops from an early stage, called a larva, into an adult. This transformation can be gradual or sudden and includes changes in body structure and function.

During metamorphosis, the larva typically undergoes drastic changes, shedding its old body and growing a new one better suited for adult life. This process can take anywhere from days to months, depending on the specific insect species. 

Some examples of insects that undergo complete metamorphosis include butterflies, moths, bees, and beetles. While others, such as grasshoppers and cockroaches, undergo incomplete metamorphosis, where they gradually change into adults without a distinct larval stage,  instead going through different stages called nymphs. 

Ultimately, metamorphosis allows insects to adapt and survive in their environments as they mature into adults, ready to reproduce and continue the cycle of life.

Larva, eggs

When an insect first hatches from its egg, it typically enters the larval stage. This is a period of growth and development where the insect will undergo multiple molts, shedding its old exoskeleton as it grows. 

During this time, the larva will eat voraciously in order to fuel its growth and metamorphosis into an adult. Some insects, such as butterflies, spend their larval stage as caterpillars feeding on plants. Others, like mosquitoes, may live in water and feed on small organisms or plant matter. 

Reproduction

Different insect species have varying ways of reproducing, but the end goal is always to produce offspring. Male and female adults often mate, with the female laying eggs to continue the insect life cycle. 

Some insects, such as bees and ants, live in highly organized societies where a single queen will lay all the eggs for the colony. The male drones and female workers take on different roles to care for the young and maintain the colony. 

Other insects, such as certain species of beetles, engage in elaborate mating rituals or fights between males to determine which will mate with the female. 

Insect reproduction can also involve interesting adaptations, such as the male bark beetle’s ability to “sing” by rubbing its body parts together to attract a mate.

Once mating is complete, and the female is able to lay its eggs, It will usually take several weeks or months for the eggs to hatch for the new generation of insects to begin their own life cycles. 

Development

The main stages of the insect life cycle are the egg, larva, pupa, and adult. It occurs in a predictable pattern for each species. But within these stages, the insect undergoes various changes as it grows and develops into its adult form. 

During the first stage, the egg, the insect embryo undergoes cell division and growth. Once it hatches, the larval stage begins. 

The larva often looks drastically different from the adult form and may have different feeding habits as well. This stage is focused on growth and development through molting or shedding their exoskeleton multiple times to accommodate their increasing size.  

Next, the pupal stage involves further changes as the insect transforms into its adult form. The pupa may be immobile and protected within a cocoon or chrysalis, or it may continue to move around actively 

Finally, in the adult stage, the insect is able to reproduce and carry out its role in the ecosystem.

Feeding and digestion

Different species of insects have a variety of feeding strategies, including herbivory, carnivory, and even scavenging. The insect’s mouthparts and digestive system are adapted to their specific diet and way of feeding. 

Insects may also have symbiotic relationships with bacteria or other organisms in their gut that aid digestion. These beneficial microbes can help break down tough plant matter or provide essential nutrients for the insect. 

Read more about what insects eat here.

Role in nature

Role for the environment

Despite the inconvenience they may cause, insects play an important role in our ecosystem. 

Many insects, such as bees, butterflies, and beetles, are pollinators responsible for the reproduction of plants which provide food for both animals and humans. Without them, our food supply would be significantly diminished 

Insects also contribute to the decomposition process by breaking down dead plants and animals into nutrients that can be reused in the environment.

Certain insects, such as dung beetles, help maintain cleanliness by disposing of animal waste.

Another benefit of having insects around is their role as natural pest control. Many insect species, such as ladybugs and wasps, prey on crop-damaging pests like aphids, thereby reducing the need for chemical pesticides. 

Insects are also food supply for various animals, including birds, fish, and small mammals. Even larger animals, such as grizzly bears, rely on the protein found in bee larvae and ants for survival. 

In terms of research and medicine, insects have been used to study genetics and have even played a role in developing various drugs and medical treatments. 

They have even been used in forensic investigations as their unique life cycles and body compositions make them valuable markers for estimating time since death. There are also Entomology societies.

While there are good things about these little critters, damage to crops,  spreading diseases, and causing structural damage to our homes are some negative effects that insects can have. 

However, it is important to remember their overall importance in maintaining a balanced ecosystem and to take measures to coexist with them in a way that minimizes harm to insects and humans. 

Role as commercial products

You may not be aware of this, but insects are actually valuable commercial products. Insects such as crickets, caterpillars, and mealworms are often used as food for animals such as fish, chickens, and even pets like reptiles and birds. 

They are also made into protein powders or flours for human consumption. One example is cricket flour, a popular alternative to wheat flour that is high in protein and nutrients.

In addition, insects also have commercial value in industries such as pharmaceuticals and biopesticides. Their bodies contain compounds that can be extracted for medicinal purposes, and their natural defenses against predators can be harnessed to create effective pesticides without the harmful side effects of synthetic chemicals.

While insects may not be a common source of commercial products in Western cultures, they have long been utilized in Asian and African countries as food and medicine. As awareness about the environmental impact of traditional livestock production grows, insect farming is becoming a more sustainable alternative.

Role as a source of raw food

If you’ve visited countries such as China,  Thailand, or Mexico, you may have seen insects sold as snacks on the street. Insects are a source of protein for many cultures and can be harvested sustainably with little impact on the environment. In fact, they emit fewer greenhouse gases and require less feed than livestock.

Popular insect foods include crickets, mealworms, grasshoppers, and ants. They can be fried, roasted, or ground into flour for baking. Other insects, such as bees and silkworms, are used to produce valuable products like honey and silk.

Origin of insects

The earliest known insects appeared during the Devonian period, about 400 million years ago.

They evolved from a group of arthropods called hexapods, including creatures such as centipedes and millipedes. Insects were an important food source for early amphibians and reptiles and later for birds and mammals as well.

The evolution of insects has led to a wide diversity of species, with over a million currently known and many more yet to be discovered and classified. They can be found in nearly every habitat on Earth, from the deepest ocean trenches to mountaintops.

Insect phylogeny, or the study of insect evolution, is an active and complex field, with new discoveries and theories constantly being proposed.

One current theory suggests that the first insects were aquatic, with adaptations for breathing and moving underwater. Over time, some insects evolved to live on land, likely aided by the development of wings for flight.

FAQs

This article has covered everything you need to know about insects. While these creatures may seem small and insignificant, they play a vital role in maintaining the balance of our ecosystem. From pollinating plants to providing food for other animals, insects should be appreciated and protected.

We hope this article has sparked a newfound interest and appreciation for insects in your life.

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