BeetlesInsects

Coleoptera Beetles

Coleoptera Beetles: The Insanely Massive Order Of The Beetles

 

Beetles are everywhere. If you explore the open grasslands of the United States or densely vegetated rainforests of Southeast Asia, the likelihood of finding a beetle will be high. Oreina cacaliae, Coleoptera (Chrysomelidae) Beetle

So much so, they make up to 40% of all described insect species on planet Earth.

This article will guide you through different beetle species and their life histories.

Beetles Classification

  • Kingdom: Animalia             
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Coleoptera 

Beetle Characteristics

  • Habitat: Nearly all habitats including: freshwater, coastal, marshland etc  
  • Diet: Some are selective herbivores, many are omnivores and some are carnivorous.
  • Color:  Some are dull shades of black or brown. Others are beautifully colored with metallic shades of red, green or blue.
  • Speed: The fastest recorded insect, the tiger beetle, can reach speeds of 9 km/h
  • Weight: Some species, such as the rhinoceros beetle, can reach weights of 100g
  • Length: Hercules beetles can reach up to 19 cm in length
  • Sexual age: It can take many years for some species to reach sexual maturity. Other species take just a few months.
  • Gestation Period: Beetles lay eggs. Eggs take between 4 – 19 days to hatch.
  • Litter Size: A female beetle can lay hundreds of eggs at any one time.
  • Number of species: 400,00+, with more being discovered. 

Beetle Facts 

Here are 10, possibly useless, but nonetheless interesting, beetle facts for you to win that next pub quiz: 

#1 Beetles are the largest group of insects.

#2 Beetles vary greatly in size. The smallest beetle is just 0.3mm, whilst the biggest is 19cm.

#3 Some beetles can make a lot of noise by tapping, clicking, banging and stridulating.

#4 Fireflies are beetles and can glow in the dark via chemical reactions involving the enzyme luciferase.

#5 There is a metallic beetle (Chrysina aurigans) so reflective, you can see your own face!

#6 Many beetles release strong chemical odors in defense. The smelliest being the burying beetles.

#7 Some beetles can change color to suit their environment. This is especially evident in the tortoise beetles.

#8 Beetles pollinate 90% of plants on Earth.

#9 Some beetles are obligate carnivores, preying on frogs.

#10 Some beetles, such as stag beetles or goliath beetles, make great pets.

What Are Beetles? The Largest Order of Insects.

The Coleoptera (beetles) is the largest single order of insects. 

So far, there are thought to be more than 400,000 beetle species described by science. It is thought that 25% of all animal species on Earth are beetles. 

Like all insects, beetles are separated into distinct sections: a head, thorax and abdomen.

Unlike other insects, however, beetles have evolved protective wing-cases, known as elytra, derived from the front pair of wings. 

The presence of elytra may have contributed to their successful colonization of a variety of harsh habitat types and niches across the globe. Elytra also protects the hindwings from physical damage, aiding with flight.

Another possible advantage to the beetles success may be due to their hard exoskeleton, which is used as protection and preventing moisture loss.   

Distribution, Diversity, and Habitat

Beetles can be found in nearly all parts of the world. The exceptions, of course, are seas and oceans and polar regions.

They are one of the most adaptable insect groups on our planet. As such, they have colonized diverse habitat types.

Although it wouldn’t be a stretch to find beetles in the open ocean, that doesn’t stop certain species from hanging around coastal regions. In fact, several hundred different species of beetle can be found throughout coastal regions of the world.

Many coastal beetle species hunt small marine prey that have been washed ashore, or amongst seaweed beds.

Of the 400,000 beetles described, approximately 13,000 are aquatic, living in freshwater habitats such as ponds, rivers, waterfalls and aquifers.

These aquatic beetles have evolved some pretty nifty tricks to thrive in this niche environment. Diving beetles trap air bubbles under their elytra, and use the oxygen reserves whilst diving for prey.

The majority of beetle species, however, are terrestrial, and are distributed worldwide. From dry desserts to wet marshlands. From deep within caves to high up on mountains. In underground root systems to within plant tissue. Beetles are unavoidable.

But scientists believe we’re only just scratching the surface of the true extent of beetle diversity. There could be as many as two million beetles waiting to be discovered!

Evolution

Ok, so we know there are a lot of beetles in the world.

But where did they all come from?

Studies suggest that one of the earliest common ancestors of beetles evolved in the late Palaeozoic (Permian era), some 295 million years ago.

A single specimen, recovered from a site in now-Germany, may hold the answers for the evolution of beetles.

Collectively referred to as “Protocoleoptera”, these Permian beetles were thought to bore into the bark of ancient trees and feed off the wood.

However, a mass extinction event is thought to have wiped out most of these Protocoleoptera beetles.

Fast forward to the Jurassic era, about 190 million years ago, and beetle diversity exploded. Flowering plants, and smaller pollinating insects, supported a greater number of beetles. Herbivorous and carnivorous beetles started to evolve.

By the end of the Cenozoic era, as recent as 1.6 million years ago, beetles were everywhere. Fossil records found across the globe are incredibly similar to extant species today, suggesting direct descendants.

Beetles Taxonomy 

The order Coleoptera comprises 125 Families in 4 Suborders (Adephaga, Archostemata, Myxophaga, and Polyphaga). 

It would be impossible to talk in general terms about such a vast panoply of organisms as the beetles. 

Instead, we’re going to be focusing on some key families: 

Bark Beetles

Family: Curculionidae 

Bark beetles are small. Typically, they are no larger than a grain of rice. They are dark red, brown or black hard-bodied insects. 

In the US alone, an estimated 600 species can be found. 

Many bark beetle species are pests, boring into living, inner-bark regions of trees. They can cause huge economic losses, and even the death of trees. 

Burying Beetles

Family: Silphidae 

Burying beetles have gained quite the gruesome reputation for themselves. 

True to their name, they bury small vertebrate carcasses in the ground and lay their eggs upon the corpse.   

Once hatched, the larvae feast upon the flesh. Yum. Both male and females release antibacterial and antifungal chemicals that prevent the carcass from rotting.

Burying beetles are often black, with bright red or orange markings on their elytra.

Chafer Beetle

Family: Scarabaeidae

Despite its small size of just 1.5cm, chafer beetles are pests in North America. 

They were introduced to the continent from mainland Europe and feed on the roots of grass, causing damage to open green spaces. 

They have a light brown colouration and can only be seen for a couple of weeks in June.

Click Beetles

Family: Elateridae 

Click beetles really can click! 

A spine, found on the beetle’s prothorax, can be snapped into a groove, found on the mesothorax (middle section). As a result, the beetle “clicks” and launches itself in the air. 

This is mostly used as predator avoidance, but also when the beetle is stuck on its back – a common occurrence for many species. 

There are around 1,000 species of click beetles in North America. 

Watch a click beetle in action by clicking the link below:

https://www.youtube.com/watch?v=2rQ8tRK2Y5w

Dung Beetles

Family: Scarabaeidae

One of the most well-known beetle species on our planet, dung beetles can be found in arid environments across the world.

They have achieved world-wide fame for their ability to comedically roll poop. 

They’re not just doing this for fun, however. Dung beetles lay their eggs in fresh poop and their larvae consume it.

Dung beetles are the only known insect to navigate using the milky way. 

Jewel Beetles

Family: Buprestoidea 

Not only do jewel beetles form one of the largest beetle families, with over 15,000 species, they are also some of the most beautiful beetles on the planet. 

Many have iridescent, metallic markings of a variety of different colors. 

They can be found in forests and woodlands of most countries around the world.

Whirligig Beetles

Family: Gyrinidae

Aquatic, whirligig beetles can be found on the surface of water bodies. There are thought to be approximately 700 species worldwide. 

When alarmed, they frantically swim in rapid circles. They can also fly. 

They are smooth and black.

Weevils

Superfamily: Curculionoidea 

Approximately 97,000 species of weevil can be found worldwide.

They have a distinctive, elongated snout. However, they are typically no larger than 1cm.

Weevils are responsible for some of the worst agricultural disasters and have cost the global economy billions of dollars.

External Morphology

Beetles are holometabolous insects with biting mouthparts and two pairs of wings. The first pair of these are modified into leathery elytra, which are not used in flight (though they may act as aerofoils). The prothorax is large, and the Mesothorax is much smaller.

Did you know: holometabolous simply refers to an insect that undergoes complete metamorphosis.

Coleoptera range in size from 0.25 mm to over 190mm long and comprise the largest and, very nearly, the smallest insects worldwide. 

But, how do we measure beetle size? Is it the beetle that weighs the most? Or is it the one with the longest body length?

Well, scientists use both.

The award for the heaviest beetle goes to the rhinoceros beetles. Or more specifically, the Actaeon beetle.

Found across Central and South America, the larvae of this species, a pale, grub-like creature, can weigh as much as 200g.

The winner for the longest beetle goes to the South American longhorn beetle, reaching lengths of over 19cm.

So, if you’re not a fan of big bugs, stay clear of South America!

But if you ask the North American feather-winged beetle, it would say bigger isn’t always better.

At just 0.25mm long, this minute beetle is a serious contender for not only smallest beetle, but smallest insect in the world.

But enough about size. Let’s take a look at some of a beetle’s external characteristics.

Head 

The sense organs can be found on a beetle’s head. These are the antennae, eyes and mouthparts. 

Antennae are very important to beetles. They are used to detect external sensory information, such as touch, smell and taste. 

There is high variation in the shape of beetle antennae – some are club-like, some are feather-like and others are saw-toothed. There are normally 11 segments to an antennae.   

Some beetle species have an enlarged antennae tip, packed full of receptors. The receptors detect chemicals and pheromones, guiding the beetle to a mate or food. 

Beetles have compound eyes and are adapted to detect motion.

Each eye comprises thousands of units, referred to as ommatidia. The more ommatidia a beetle possesses, the better its motion detection. 

The mouthparts of a beetle are referred to as mandibulate. They are adapted for grinding, chewing, pinching or crushing solid food. There are 5 components that form the mandibulate: 

·   Labrum – acts as a front lip to contain food in the mouth.

·   Mandibles – laterally (side-to-side) operated jaws, used for crushing etc.

·   Maxillae – a pair of sensory appendages, extending from the side of the head.

·   Hypopharynx – a tongue-like structure that mixes food with saliva

·   Labium – a modified back lip 

Thorax

The thorax is the middle region of a beetle’s body. It comprises three segments: prothorax, mesothorax and metathorax.

The thorax is the site of attachment for the wings and legs, enabling beetles to fly and walk.

Legs

Adult beetles have three pairs of legs. Each pair of legs is joined at each section of the thorax.

Small, claw-like structures can be found at the last segment of the legs of some species. These help beetles grip onto vertical substrates, such as tree trucks.

The legs of a beetle have adapted to aid in its lifestyle. Predatory ground beetles, such as the tiger beetle, have long and slender legs that allow it to run at great speeds to catch its prey. These are known as cursorial legs.

Other species have legs adapted to swimming. This is known as a natatorial leg. Covered in hair-like seta, the legs enable species of diving beetles to swim to great depths. 

Abdomen 

The last section of the beetle’s body, the abdomen, is typically the largest segment and contains the digestive and reproductive organs

The abdomen has tiny holes, called spiracles, in which oxygen-rich air passes through and directly into the body via tracheal tubes. This is how beetles breathe without lungs.

The upper side of the abdomen is covered by the elytra, or sclerotized forewings, which aids in the protection of the delicate hindwings. 

The abdomen is heavily chitinized, but flexible. 

Wings

Unlike most insects, which have two pairs of wings, beetles just have one pair of hindwings. This is due to the evolution of the sclerotized elytra. 

The elytra meet along the elytral suture, a pronounced line running along the length of the abdomen. In some species, most notably ground beetles, the elytra has fused altogether and wings are not present. 

The elytra are often heavily textured with grooves; a potential indication of the remaining framework of membranous veins.

Anatomy and Physiology

Digestive System

The digestive system varies for certain beetle groups.

Digestion in herbivorous beetles takes place in the midgut, or mesenteron, via enzymatic digestion.

Digestion in carnivorous beetles, however, occurs in the crop; a food-storage organ. Salivary enzymes, along with tooth-like denticles, begin to break down food. 

Nervous system

Beetles possess a simple nervous system, consisting of a dorsal brain and a ventral nerve cord, as well as paired segmental ganglia. 

The brain of a beetle houses three pairs of fused ganglia, each of which controls a certain area or activities within the body. 

Respiratory system 

Beetles do not have lungs. Instead, they have small holes along the abdomen, called spiracles, that allow the flow of oxygen through the beetle’s body. 

This influx of oxygen, along with the exhalation of carbon dioxide, is via a tracheal system. Oxygen mixes with free-flowing haemocoel within the body cavity. 

Certain beetle species, especially aquatic species, have evolved ways to have a continuous flow of oxygen, even underwater.

They trap an air bubble under their elytra, which covers some of their spiracles, allowing air to enter into the trachea. 

Circulatory system

Like other insects, beetles have an open circulatory system. This means they do not possess veins, arteries or capillaries. 

They do not have blood. Instead, they have hemolymph – a yellowish fluid that remains in direct contact with the beetles tissues. 

A primitive heart-like organ can be found in the abdomen region of the dorsal vessel. 

Haemolymph flows into the heart when relaxed. The heart contracts and pumps hemolymph through the vessel, towards the insect’s head. It flows freely back through the body and into the heart again. 

Specialized organs 

Many beetle species produce specific pheromones to attract mates. These pheromones are produced in a variety of specialized organs. These include:

 ·   Epithelial cells of the subfamily Rutelinae

·   Eversible glands in the subfamily Melolonthinae

Beetles also have tympanal organs. These are hearing organs, consisting of a thin membrane stretched over an air-filled cavity and sensory neurons. 

Beetles that possess tympanal organs can hear ultrasonic frequencies, suggesting a possible defense mechanism against the echolocation of predatory bats.

Life Cycle

Most beetle species undergo complete metamorphosis. Young of recently hatched eggs do not resemble mature adults. Beetles go through four main stages:

Egg

Most beetle species lay anywhere between a few dozen to hundreds of thousands of eggs in her lifetime.

Beetle eggs are generally soft and smooth, and laid in big clutches.

However, some species of beetles take parental care very seriously. The giraffe weevils lay a single egg on a leaf. It will then delicately roll the leaf around the egg to enclose it in a protective capsule until it hatches. 

Larvae

Eggs hatch into the larval form. 

Larvae feed ferociously, often doubling or even tripling their size. The larval phase can be as long as several years. 

Beetle larvae differ from other insects. Many have a hard, dark head with chewing mouthparts. 

All beetle larvae go through several developmental stages between each molt before they pupate.

Pupae

The pupa is the transformation between an immature and mature insect. It is a period of complete physiological and morphological change. In this stage, appendages are not fully attached to the body.

It can take upwards of 15 days for the larvae to complete the pupation process.

A sexually mature adult beetle will emerge from the pupa.

Adult

Adult beetles have a very varied lifestyle, depending on the species. Some, such as the splendour beetle, can live for as long as 30 years, hidden away within trees.

Some, such as the carpet beetle, only have a couple of weeks to live. During this time, the beetle will attempt to mate with as many females as possible.

Anti-predator adaptations and Camouflage

Mimicry 

Mimicry is when two separate organisms resemble one another. This could be between related or unrelated species. 

Mimicry functions as an anti-predator adaptation, and many beetle species have evolved different forms of mimicry. Let’s take a look:

Batesian mimicry

Batesian mimicry is when a harmless species mimics a harmful species.

Certain longhorn beetles successfully mimic toxic wasps. Not only do the beetles look similar, by using the same colouration and patterns, but also displays similar behavior.

Mullerian mimicry

Mullerian mimicry is when two unrelated, but harmful, species look the same. This increases the chances of predators leaving the mimic alone. 

Beetles belonging to the Lycid family are such species that use mullerian mimicry. It is estimated that nearly 600 different species of these toxic beetles share similar physical traits to ward off predators. 

Aposematism 

Aposematism is the use of warning colouration to advertise an individual’s toxicity, or harmfulness.

Aposematism is relatively common in the animal kingdom, and beetles readily use aposematism to display warnings. 

Blister beetles, with their striking black and yellow markings, and ladybirds, with their vibrant red and white markings, are two examples of beetles that use aposematism. 

Chemical Defenses

Chemical defenses normally go hand-in-hand with aposematism. The use of bright warning colorations advertise to predators not to get too close. 

If the warning signals do not work, some beetles resort to chemical warfare. 

Many beetles acquire toxic chemicals from their diet (plants or other insects). 

Other beetles, such as the bombardier beetles, produce chemicals within specialized glands, known as pygidial glands. The gland comprises two chambers: one for hydrogen peroxide and the other for enzymes. 

When mixed together, the reaction is explosive! Temperatures over 100°C are generated and can be aimed directly at predators. 

Other Defenses 

Beetles within the Carabidae family are often large and ground-dwelling. They are not toxic and do not mimic toxic species? 

So, how do they defend themselves? 

With armor! 

Many species, such as the rhinoceros beetle, have large, sclerotized horns or mandibles which they can use to defend themselves.

Role with nature

Parasitism

When we think of parasites, fleas, ticks and lice may come to mind. 

But beetles can also be parasites. 

One parasitic beetle, the aptly named beaver beetle, parasitises beavers. Strikingly similar to fleas, these minute beetles are flat and wingless to help navigate the beavers’ thick hair.   

Other beetles, such as the small hive beetle, are kleptoparasites. They can be found in bee colonies, feeding off stored honey and pollen. 

Did you know: Kleptoparasites are species that steal food from another species.

Some species of beetles, albeit a small percentage, are even parasitoids, laying their eggs and feeding upon host insects. Some ground beetles exhibit this behavior. 

Pollination 

Beetles are one of the most important pollinators on our planet, responsible for pollinating up to 90% of all plant species. 

However, most plant species do not rely solely on beetle pollination (due to their tendency to eat the flowers). 

Those flowers that do depend solely on beetles for pollination are referred to as cantharophilus plants. These plants tend to be greenish in color and produce heavy scents of fruit, spice or rotting material. 

Scavengers 

Like vultures, certain beetle species are scavengers. They are paramount to the health of our ecosystems.

Beetles are responsible for recycling nutrients back into the soil and preventing the spread of infectious diseases. 

Dung beetles are referred to as coprophagous, which means they consume poop. Although gross to you and I, they perform the incredibly important task of recycling. A task that would cost the human population billions of dollars per year. 

In the US cattle industry alone, dung beetles are thought responsible for saving over US$380 per year – just from burying dung!

Learn more about the dung beetle by following the link below:

https://www.youtube.com/watch?v=I1RHmSm36aE

Relationship to humans

As pests 

Beetles are important, there’s no doubt about it. 

However, they can also become quite the agricultural nuisance. Many species feed on economically important crops, bore into timber wood and infest our homes. 

The cotton boll weevil, no larger than 6mm, is responsible for $13billion worth of damage to the cotton industry per year! 

Plantations of conifer trees fall victim to bark beetles, which tunnel through the living portion within the tree.

The Colorado potato beetle causes vast amounts of damage to potato, tomato and eggplant crops. Unfortunately, some populations are now immune to all major insecticides. 

Beneficial Resources 

Despite their drawbacks, beetles are incredibly beneficial. 

As we touched upon, many species are essential for nutrient recycling and preventing the build-up of harmful pathogens. 

Predatory beetles, such as the ladybird, control populations of destructive fly pets, such as aphids and whitefly. 

Nutrient recycling and pest control benefit the global economy, and the health of global citizens, significantly. 

As food 

Across the globe, beetles are readily consumed by humans – both in their larval and adult stage. 

Mealworms, the larvae of the mealworm beetle, are high in minerals and vitamins, including protein. They can be grounded into a flour and added as a nutritional flour substitute. 

You can bake them, roast them or fry them with your favorite spices to make a tasty snack. 

As biodiversity indicators

Some species of beetle are highly specific in where they live. As such, they can be used to assess the quality of the ecosystem, based on the number of beetles present.

Found in the soil, wetlands, leaf litter and waterways, beetles can be used to assess the effects of human activities in these fragile ecosystems. Beetles are extremely sensitive to environmental changes, and react quickly to environmental modifications.

FAQs

  • What is the common name for Coleoptera? 

Beetles form the order Coleoptera. This also includes the weevils.

  • Are Beetles herbivores, carnivores, or omnivores?

Depending on the species, beetles can be herbivores, omnivores, carnivores and fungivores.

  • Are beetles harmful or helpful? 

Some species can be harmful and cause damage to crops and infrastructure. Other species are incredibly helpful to the human population.

  • Do beetles carry diseases?

Beetles can carry diseases, especially those that feed off feces or corpses.

  • How do I get rid of beetles in my house? 

Prevention methods include cleaning thoroughly after eating. Natural remedies to repel beetles include peppermint and lavender oil.

  • Why do I have beetles in my house?

Some species of beetle eat wood and can be found in furniture. Other species are attracted to open food.

  • Why do beetles come out at night?

Typically, there are fewer predators at night.

  • What are beetles attracted to? 

Beetles are attracted to lights. They are also attracted to food. This can be in the form of open trash or leaving food products uncovered.

  • What month do beetles go away? 

Towards the end of summer (late August to early September), some beetle species start to die out.

Conclusion

Beetles have been around for millions of years. Evolutionarily speaking, they haven’t really changed that much in this time.

They have, however, expanded into nearly every continent on Earth. Here, they have exploited an array of niches.

Although some beetle species negatively affect humans, the majority of species are extremely beneficial. Without beetles, we would be in a world of sh*t. Literally. 

References 

  • Nature, Scientific Reports, Article, Oct 2016
  • UC San Diego, Scripps Institution of Oceanography, April 2020
  • National Library of Medicine, Ecology, Jun 2016
  • Kerbteir.de, Phylogeny of the beatles, C. Benisch, 2010
  • Evolutionary Biology, Research Article, Nov 2021
  • University of California Agriculture and Natural Resources, bark beetles, Nov 2008
  • University of Minnesota, Department of Entomology, Revisited Nov 2022
  • ScienceDirect, Current Biology, Feb 2013
  • Arizona State University, Ask a Biologist
  • ResearchGate, Book, Jan 2016
  • NC State, Agriculture and Life Sciences
  • National Library of Medicine, Annual Review of Entomology
  • Springer Link, Encyclopedia of Entomology, 2008
  • University of California, PollenNation, Revisited 2022
  • Taylor and Francis Online, Human and Ecological Risk Assessment, Sept 2017

Gordon Ramel

Gordon is an ecologist with two degrees from Exeter University. He's also a teacher, a poet and the owner of 1,152 books. Oh - and he wrote this website.

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