Dominic Stone
Beetles, like all insects, have muscles. They have an open circulatory system and lack an extensive network of arteries and veins. Instead, their hemolymph bathes their tissues directly, transporting nutrients and carrying waste products from the organs to the malpighian tubules. Beetles have powerful muscles that operate their wings and legs, and they also contain visceral and cardiac muscles. The skeletal muscles of beetles are bundles of multinucleated cells called fibres, which attach at each end to the exoskeleton.
| Characteristics | Values |
|---|---|
| Do beetles have muscles? | Yes |
| What type of muscles do beetles have? | Skeletal, visceral, and cardiac muscles |
| What are skeletal muscles? | Bundles of multinucleated cells called muscle fibers that attach at each end to the exoskeleton |
| What are visceral muscles? | Cause movement of the gut, malpighian tubules, and parts of the reproductive system |
| What are cardiac muscles? | Cause contraction of tissue sheets and vessels associated with the circulatory system |
| What is the function of the 3rd axillary (3Ax) muscle in beetles? | It is a minor flight muscle that pulls the beating wing to attenuate the stroke amplitude, leading to left-right turning in flight or wing folding to cease flying |
| What is the difference between major and minor flight muscles? | Major flight muscles have shorter myofilaments (3.5 μm) with a smaller ratio (1:3) while minor flight muscles have long myofilaments (5 μm) with a ratio of 1:5 or 1:6 |
| What is the exoskeleton made of? | An inert compound made mostly of a carbohydrate called chitin (polyacetylglucosamine) |
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What You'll Learn
Beetles have an external skeleton or exoskeleton
Beetles are insects, and insects have exoskeletons. An exoskeleton is a hard external skeleton, derived from the Greek words "exo" meaning "outside" and "skeleton". Exoskeletons are found in invertebrates, or animals without backbones, and insects are the largest group of animals with exoskeletons. Exoskeletons are made of a substance called chitin, a complex sugar molecule that is tough yet flexible. The more proteins and minerals in an exoskeleton, the harder and stiffer it is, while a higher chitin component provides more flexibility.
Beetles, like other insects, have hard exoskeletons to protect their soft bodies. The exoskeletons of arthropods, the group of invertebrates that includes insects, consist of hard plates, called sclerites, connected by more flexible material at the joints and between body segments. Beetles' exoskeletons are made of chitin, strengthened with elastic proteins and minerals such as calcium carbonate.
The exoskeletons of insects have joints or bendable sections that allow the animals to move easily. The three biggest and most visible joints in an insect's exoskeleton are found between the head, thorax, and abdomen. The skeletal muscles of insects are bundles of long, multinucleated cells called muscle fibres, which attach at each end to the exoskeleton. These muscles span the joints of the exoskeleton and cause bending or stabilization of the joint when active.
Unlike vertebrate endoskeletons, arthropod exoskeletons cannot increase in size as the animal grows. Instead, arthropods grow in stages by moulting their exoskeletons and replacing them with larger ones. During moulting, the animal's body is vulnerable to predators as the new exoskeleton is soft at first. As the chitin and protein molecules bind together, the exoskeleton hardens.
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The exoskeleton is made of a compound called chitin
Beetles, like all insects, have muscles. The skeletal muscles of insects are bundles of multinucleated cells called muscle fibres, which attach at each end to the exoskeleton. The exoskeleton is a tough, resilient outer covering that protects the beetle's body. It is made of a compound called chitin, a long-chain polymer of N-acetylglucosamine, which is a derivative of glucose.
Chitin is a key component of the exoskeleton, providing tensile strength and flexibility. The exoskeleton is composed of four layers: the epicuticle, procuticle, epidermis, and basement membrane. The outermost layer, the epicuticle, acts as a barrier against desiccation, or drying out. The procuticle, which lies just beneath the epicuticle, provides strength and flexibility and is composed of fibrous chains of alpha-chitin within a matrix of silk-like and globular proteins. The relative abundance of chitin and protein varies across the exoskeleton, with softer parts containing a higher proportion of chitin.
The procuticle is further divided into the exocuticle and the endocuticle, with the potential for another layer called the mesocuticle in between. The exocuticle is the layer where thickening, armouring, and biomineralization occur. Biomineralization is a process in which mineral crystals, primarily calcium carbonate, are deposited among the chitin and protein molecules, reinforcing the exoskeleton and providing additional hardness and resistance to compression.
The internal surface of the exoskeleton is often infolded, forming structures called apodemes that serve as attachment points for muscles. These invaginations, or inward folds, increase the surface area for muscle attachment and contribute to the overall strength and rigidity of the exoskeleton. Beetles and other insects owe their incredible strength to the geometry of their musculature, which provides optimal leverage for the movement of their appendages.
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Beetles have three body sections: head, thorax, and abdomen
Beetles, like all insects, have a body divided into three sections: the head, the thorax, and the abdomen. This is known as the insect's body tagmata. The head is specialised for sensory input and food intake, with mouthparts located outside of the head capsule. The head capsule is made up of six fused segments, each with a pair of ganglia, or a cluster of nerve cells outside of the brain.
The thorax is the middle body region and is the anchor point for the legs and wings. It is composed of three segments, with a pair of legs located on each segment, and two pairs of wings found on the second and third segments. The thorax is where the muscles are located that help the beetle walk, jump and fly. Beetles have a total of six legs, and when they walk, they always have a tripod of three legs on the ground, with the other three legs lifted off the ground.
The abdomen is the posterior or last of the three body regions. It is the biggest body part and is composed of 9, 10, or 11 segments, depending on the source and type of beetle. The abdomen holds the beetle's digestive system, respiratory system, reproductive organs, and visceral muscles. Each abdominal segment has a pair of spiracles, the openings into the air-tube (tracheal) system.
The insect body is different from a human body in that insects have an exoskeleton, a hard outer layer made of chitin, instead of an interior skeleton. The exoskeleton varies in beetles from very horny and rigid to soft and flexible, but it usually consists of hard plates (sclerites) separated by flexible membranes.
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Beetles have powerful muscles that operate their wings and legs
Beetles, like all insects, have an external skeleton called the exoskeleton, which is made mostly of a carbohydrate called chitin. The exoskeleton is essential for muscle attachment and serves as protection. Beetles have powerful muscles that operate their wings and legs. These muscles are attached to the exoskeleton and are bundles of long, multinucleated cells called muscle fibres. Beetles have three pairs of well-developed legs with a strong femur and tibia and five or fewer tarsal segments.
The Mecynorrhina torquata beetle has a unique minor flight muscle called the third axillary (3Ax) muscle. This muscle is small in volume but generates large amounts of power, allowing the beetle to turn left or right in flight or fold its wings when it wants to stop flying. The 3Ax muscle has long myofilaments and a thick-to-thin filament ratio of 1:5 or 1:6, which contributes to its strength.
Beetles also have visceral and cardiac muscles in addition to their skeletal muscles. The visceral muscles control the movement of the gut, malpighian tubules, and reproductive system, while the cardiac muscles contract tissue sheets and vessels in the circulatory system. Beetles have an open circulatory system, meaning they lack a complex network of arteries and veins, and their hemolymph directly bathes their tissues and organs. The hemolymph delivers nutrients and removes waste, with the help of free cells called hemocytes that destroy foreign microorganisms.
The powerful muscles of beetles enable them to fly, escape dangerous situations, and seek mates over vast distances. Beetles' wings are essential for their survival and reproduction, and their ability to fly is a significant advantage over other insects that cannot. The combination of strong muscles, a lightweight exoskeleton, and efficient circulatory system allows beetles to be agile and manoeuvrable in their environment.
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Beetles have cardiac and visceral muscles in addition to skeletal muscles
Beetles, like all insects, have muscles. They have cardiac and visceral muscles in addition to skeletal muscles.
Cardiac muscle, also called the myocardium, is one of the three major categories of muscles found in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. Beetles, like other insects, have a heart that pumps haemolymph, a blood substitute, into circulation.
Unlike skeletal muscle, cardiac muscle is under involuntary control. Cardiac muscle cells, or cardiomyocytes, are striated, branched, and contain many mitochondria. Each cardiomyocyte contains a single, centrally located nucleus surrounded by a cell membrane called the sarcolemma. The sarcolemma of cardiac muscle cells contains voltage-gated calcium channels, specialised ion channels that skeletal muscle does not possess.
Visceral muscles are muscles that work automatically and are found in the organs of the body, such as the stomach and lungs. They are also known as smooth muscles and are found in the walls of internal organs such as the stomach, intestines, and bladder. These muscles are responsible for involuntary movements such as digestion and breathing.
Skeletal muscles, on the other hand, are attached to bones and allow for movement. They are typically under voluntary control, meaning that they respond to signals from the brain. In insect muscle systems, there is often an elastic-like tissue that compresses upon the contraction of one muscle. The energy from this compression is then released to extend the muscle back to its resting position. This eliminates the need for antagonistic muscles, which contributes to the preservation of low mass.
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Frequently asked questions
Yes, beetles have muscles.
Beetles have skeletal muscles, visceral muscles, and cardiac muscles.
Beetle skeletal muscles are bundles of multinucleated cells called muscle fibers. They attach at each end to the exoskeleton and cause the bending or stabilization of the joints.
Beetle muscles are made up of long myofilaments. The ratio of thick (myosin) filaments to thin (actin) filaments is approximately 1:5 or 1:6.
