Use this glossary to explore terms found in the virtual beetle dissection or to increase your knowledge of anatomy & physiology. You will find extra terms here that are not included in the virtual beetle dissection. If you are looking for something specific, just use the page search tool on your computer (likely Control F) and type in what you are hoping to find.

General Anatomy & Physiology Terms

• Dorsal: top side
• Ventral: underside
• Lateral: left and right sides
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  Scarab beetles are found all over the world. This is a scarab dung beetle found in Arizona. He is very colorful and has a large horn on his head. Click to enlarge.

  Anatomy: a branch of biology that studies body structures of humans or other organisms
• Physiology: a branch of biology that studies how organisms function
• Micro-CT: a technology that uses x-rays to produce a series of images that are slices through a structure or an organism. These slices can be put together to form a 3-D image or model.
• Scarab beetle: a beetle in the family Scarabaeidae. These are stout beetles and males often have horns used for competition against other males. They are found on all continents but Antarctica. The ecology of scarab beetles varies greatly – some are dung beetles, some fruit eaters, some are flower chafers (eaters), and some are pests.

External Insect Anatomy Terms

• Cuticle: outer layer of the exoskeleton
• Exoskeleton: hard outer surface of the beetle body that protects the inside of the beetle and acts as a skeleton. Muscles and other internal parts attach to the exoskeleton.
• Apodeme: an internal ridge of the exoskeleton where muscles attach.
• Sclerotization: hardening and darkening of the exoskeleton as the beetle gets older.
• Seta: a hair found on the outside of the beetle’s body that can be used for protection, sensing air movement and touch, and other tasks. Setae is the plural form.
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  Like this green tiger beetle, many insects have hairs called setae that help them sense movement around them. Click to enlarge.

  Head: hard body segment at the front of the beetle that houses the brain, mouthparts, eyes, antennae, horns, and some other important parts.
• Thorax: middle segment of the beetle that mostly contains the leg muscles and flight muscles. All legs and wings attach to this segment. Muscles that move the neck and support the head are also found here. The esophagus, heart, ventral nerve cord, and ganglia can also be found here.
• Abdomen: hind segment of the beetle that contains the intestines, reproductive parts (testes and penis in males or eggs in females), and many air sacs and trachea.
• Prothorax: forward-most section of the thorax that contains the leg muscles and muscles that support the head and neck.
• Metathorax: second segment of the thorax that contains mostly flight muscles.
• Sclerite: a hard plate of exoskeleton found on the dorsal (top) surface of the beetle.
• Sternite: a hard plate of exoskeleton found on the ventral (bottom) surface of the beetle.
• Sclerotin: protein material in the cuticle that allows the cuticle to harden and darken.
• Chitin: material made of polysaccharides (carbohydrates) that makes up most of the cuticle.

Insect Head Anatomy Terms

• Antenna: a structure used for sampling chemicals in the air for olfaction, taste, and air movement. In the beetle dissection, the antennae are composed of several segments that can splay outward like a fan.
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  A close-up of a scarab beetle head shows many of the head features including antennae, compound eyes, and palps. Click to enlarge.

  Johnston’s organ: organ in the antennae that senses the movement of air.
• Compound eye: an eye composed of many (oftentimes thousands) smaller units called facets that work together to form an image. The beetles in the dissection can see colors, ultraviolet light, and even polarized light.
• Palpus: a mouthpart; plural, they are palps.
• Maxilla: a mouthpart; plural, they are maxillae.
• Mandible: a mouthpart.
• Ocellus: an extra eye that is mostly used for sensing the brightness of light and movement of large objects. Insects usually have multiple ocelli.
• Esophagus: a tube that carries food from the mouth to the crop where it can be stored until digestion in the intestines.

Insect Thorax Terms

• Pronotum: a plate-like structure that covers the prothorax
• Prothoracic legs: the front pair of legs or forelegs.
• Mesothoracic legs: the middle pair of legs or midlegs.
• Metathoracic legs: the back pair of legs or hindlegs
• Coxa: a joint where a leg attaches
• Trochanter: the first short section of the leg attached to the coxa.
• Femur: the longest segment of the leg between the trochanter and tibia. The femur can have large spikes used for climbing and protection.
• Tibia: the long section of the leg between the femur and tarsi. The tibia can have large spikes used for climbing and protection.
• Tarsus: a small section of the leg that can be easily bent and have hooks used for climbing and walking.
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  Wings are part of the thorax and are unfolded when used in flying. Click to enlarge.

  Wing: a large, thin, flat (membranous) section of cuticle attached to the thorax that is used for flying. When beetles are not flying, wings are folded and stored underneath the elytra.
• Cross-vein: a hard and thick piece of  wing that is used for support, flapping, and folding the wings.
• Elytron: a hard, shell-like covering that protects the wings when the beetle is not flying. Elytra are modified forewings that are not used to fly.
• Skeletal muscle: a muscle attached to the cuticle that moves different parts of the beetle.Skeletal muscles can be moved voluntarily.
• Striation: a long parallel line in a muscle. Each muscle is made of many smaller contractile units that appear striped. In the beetle x-rays, the muscles appear striped because of trachea that run through the muscles to supply oxygen.
• Smooth muscles: muscles that are used for movement in the digestive system, reproductive system, and other parts of the body that do not move voluntarily.
• Direct flight muscle: a muscle that is used primarily to control the wings. In some insects, like these beetles, some direct flight muscles are also used for power.
• Indirect flight muscle: a muscle that is attached to either the top and bottom cuticle of the thorax or the front and back cuticle of thorax. When indirect flight muscles move, they deform the cuticle that they are attached to in order to move the wings.

Insect Abdomen Terms

• Testis: a sex organ that produces sperm in males.
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  The aedeagus or penis is used by males during mating. Click to enlarge.

  Aedeagus: also called the penis. This organ is found in males and used to deliver sperm into the female during mating.
• Foregut: the first portion of the intestine that food moves through as it is digested.
• Midgut: the middle part of the intestine (site of most digestion and absorption).
• Hindgut: the last part of the intestine, where nutrients, salts, and water can be absorbed, and some toxins excreted. This functions like part of the kidney, being the most important site for regulation of water and salt content of the insect.
• Saliva: made in salivary glands in the head. Saliva has enzymes that moisten and begin to digest food as the beetle eats.
• Malpighian tubule: a thin tubular structure that functions like part of the kidneys of humans. These actively create a fluid that flows into the gut, containing most of the components of the blood, and some secreted toxins.
• Rectum: the last portion of the hindgut.
• Ovary: an organ where eggs are produced in females. The ovaries are difficult to distinguish from the eggs in the virtual beetle dissection because the eggs of adult females can be very large and can stretch the ovaries.

Insect Nervous System Terms

• Brain: found in the head. The brain processes sensory information from the eyes, antennae, mouthparts, sensory hairs, and other parts of the body. It receives information from the ventral nerve cord and delivers information to the body that is used to make decisions and react to the environment. Learning processes also occur in the brain.
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  Most insects have one or more ganglia that control the local movements of a body segment. Click to enlarge.

  Subesophageal ganglion: a section of the brain found underneath the esophagus and processes information from the mouthparts.
• Ventral nerve cord: a nerve cord, similar to a spinal cord, found near the ventral cuticle of the beetle.
• Ganglion: a concentrated area where nerves come together within body segments. Each body segment in an insect usually has its own ganglion that controls local movements. Two or more ganglia can be combined in some insects.
• Visual lobe: a part of the brain closest to the eyes that processes information from the eyes. These parts of the brain are called the lobula, medulla, and lamina.
• Olfactory lobe: a part of the brain that processes information from the antennae. These are also called antennal lobes.
• Mushroom bodies: a part of the brain that processes information from the visual and olfactory lobes together. This area of the brain is important for decision making and learning.

Insect Endocrine System Terms

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  Hormones released by the endocrine glands are an important part of the molting process. Click to enlarge.

  Fat body: diffuse tissue found throughout the body that appears yellowish or brownish in color. Fat body is often found close to the cuticle, surrounding the heart, or near muscles. Hormones can be made in the fat body but fat body is also used for energy storage and detoxification.
• Endocrine gland: an organ that specializes in manufacturing hormones. In insects the most important endocrine glands are the corpora cardiaca, corpora allata, and prothoracic glands. These produce hormones that are important for growth and metamorphosis.
• Neurosecretory cells: cells in the brain the produce molecules important for signaling functions such as growth, reproduction, regulation of blood sugar levels, and metamorphosis.

Insect Circulatory System Terms

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  The dorsal heart is a long tube that contracts in waves. Click to enlarge.

  Hemolymph: blood. Unlike blood in humans, beetle blood is not red because it does not have hemoglobin molecules, the protein that makes blood red and binds to oxygen and carbon dioxide.
• Dorsal heart: a tubular heart that pumps hemolymph using wave-like peristalsis movements, similar to the movement in the digestive system. Hemolymph is pumped forward to the head, spreads throughout the body tissues and is recollected into the heart at the hind end of the beetle. The heart is found very close to the dorsal cuticle and is surrounded by fat body. 

Insect Respiratory System Terms

• Trachea: a tube that delivers air (containing oxygen) to the tissues, and moves carbon dioxide produced by the tissues out of the body through the spiracles. Smaller trachea are called tracheoles and can be only a few micrometers wide.  
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  Air sacs and tracheae are responsible for delivering and storing air in insects. Click to enlarge.

  Air sac: a flexible, rounded portion of a tracheal tube that can store gases or act as bellows to move air when the beetle pumps its abdomen. Many air sacs are also used for cushioning and hydraulic movement at joints. Air sacs can be many sizes and are found throughout the body.
• Taenidia: a small stiff band on trachea that keeps tracheal passages open so air can flow through.
• Spiracle: a small opening in the exoskeleton that allows air in and out of the body as the beetle breathes. Air that enters a spiracle can go through tracheae and air sacs to get to the tissues. Most spiracles have valves or gates so they can be open or closed.

Additional images via Wikimedia Commons. Damselfly image by Sam Droege.