SciOly Entomology

Insect Anatomy

Insect Leg Anatomy

What were the ancestors of present-day insects likely like?

Worm-like arthropods with a simple mouth opening near the front of a bilaterally symmetrical body.

How did the mouthparts of insects evolve?

They adapted for gathering and manipulating solid food as insects evolved and changed their diet.

What is adaptive radiation?

An evolutionary process in which two or more populations diverge from a common ancestor due to different selective pressures.

Why do entomologists pay close attention to insect mouthparts?

The structure of mouthparts allows inference about the type of food consumed — plant or animal, solid or liquid, dead or alive.

What does the phrase 'Form Follows Function' imply in biology?

The structure of an organism is closely related to its function, particularly in relation to its diet.

What can studying an insect's diet reveal?

It can provide information about its ecology and natural history.

Give an example of variability in insects due to adaptive radiation.

Variability in legs, wings, and antennae.

What does the evolution of insects demonstrate about their adaptability?

Insects became more complex, expanded in range, and adapted to new food resources over time.

What is the significance of the mouthparts in relation to insect ecology?

Mouthparts indicate the type of food consumed, which is crucial for understanding the insect's role in the ecosystem.

How does the structure of mouthparts correlate with an insect's lifestyle?

The structure changes in accordance with the insect's evolving diet and lifestyle.

What evolutionary process can be observed in the insect world?

Adaptive radiation, evident in the diversity of insect forms and functions.

Mandibulate mouthparts

Mouthparts adapted for grinding, chewing, pinching, or crushing bits of solid food.

Labrum

A simple plate-like sclerite that serves as a front lip to help contain the food.

Mandibles

A pair of jaws for crushing or grinding the food that operate from side to side.

Maxillae

Paired appendages that assist in manipulating food.

Cardo

Basal sclerite of the maxillae that articulates with the head capsule.

Stipes

Medial sclerite of the maxillae that supports a sensory palp.

Galea and Lacinia

Distal sclerites of the maxillae that act as fork and spoon to manipulate the food.

Hypopharynx

A tongue-like process that helps mix food and saliva.

Labium

A back lip derived from a pair of fused appendages along the midline.

Postmentum

Fused basal sclerites of the labium that articulate with the head.

Prementum

Distal sclerites of the labium that support sensory palps and divide apically into four lobes.

Glossae

The two innermost lobes of the prementum.

Paraglossae

The two outermost lobes of the prementum.

The maxillae has which 4 parts?

Cardo, stipes, galea & lacinia

Parts of the labium

Postmentum & prementum

sclerite

a component section of an exoskeleton, especially each of the plates forming the skeleton of an arthropod.

sensory palps

manipulating and smelling food

glossae

The two median ligular lobes of the labium, each provided with a muscle arising in the prementum.

paraglossae

The lateral ligular lobes of the labium, each with a muscle arising in the prementum

Mandibulate mouthparts

Mandibles

Mandibles image

What is the third functional region of an insect's body?

The abdomen

Where is the abdomen located in relation to the thorax?

Just behind the thorax

What is the appearance of the junction between the thorax and abdomen in some insects?

It can be very narrow (petiolate), giving the appearance of a 'wasp-waist'

From what type of ancestors did insects arise?

Primitive arthropod ancestors with eleven-segmented abdomens

Which present-day insects still have remnants of the eleven-segmented abdomen (or remnants of them)?

Silverfish and mayflies

How has natural selection affected the number of abdominal segments in advanced insect groups?

It has contributed to a reduction in the number of segments, sometimes to as few as six or seven (beetles, flies, etc.)

In most insects, the junction between thorax and abdomen is ____

broad

abdomen bugs

What are the two main sclerites that make up each segment of the insect abdomen?

The tergum (dorsal sclerite) and the sternum (ventral sclerite)

How are the tergum and sternum joined in the insect abdomen?

They are joined laterally by a pleural membrane.

What function does the telescoping of front margins of abdominal segments serve? Note: The front margins of each segment often "telescope" inside the sclerites of the preceding segment.

It allows the abdomen to expand and contract in response to skeletal muscle actions.

Where are spiracles typically located in adult insects?

Near the pleural membrane on each side of the first eight abdominal segments.

pleural membrane

membrane that encloses the lungs

What is the purpose of spiracles in insects?

They serve as openings to the respiratory system.

True / False: Some spiracles may be permanently closed, but still represented by a dimple in the sclerite.

True

What structures / sclerites protect the anus at the back of the insect abdomen?

A dorsal epiproct and a pair of lateral paraprocts.

epiproct

a process or appendage just above the anus, appearing to rise from the 10th abdominal segment

paraprocts

A pair of lobes located below and on each side of the anus.

What are cerci and where are they located?

Cerci are sensory organs located near the anterior margin of the paraprocts.

True / False: Cerci are tactilce (touch) receptors.

True

Why are cerci considered a primitive trait in insects?

Because they are absent in the hemipteroid and holometabolous orders.

What is located just below the anus in the insect abdomen?

The insect's genital opening.

What forms the external genitalia in insects?

Specialized sclerites surrounding the genital opening.

What is the ovipositor and in which sex of insects is it found?

The ovipositor is an egg-laying mechanism found in females, formed by paired appendages of the eighth and ninth abdominal segments.

What is the role of the abdominal segments in insects?

They facilitate movement and house important reproductive and digestive structures.

What is the primary function of the pleural membrane in the insect abdomen?

It allows flexibility and movement between the tergum and sternum.

ovipositor image

ovipositor image

The ovipositor consists of

4 valvifers and 6 valvulae

valvifers

basal sclerites with muscle attachments (F6)

valvulae

apical sclerites which guide the egg as it emerges from the female's body (5 & 3)

What is the function of the aedeagus in male insects?

The aedeagus is a tube-like structure that enters the female's body during copulation.

What are claspers in the context of insect genitalia?

Claspers are part of the external genitalia that facilitate mating.

How do the genital sclerites vary among insect species?

The structure of genital sclerites differs from species to species, which usually prevents inter-species hybridization.

Why are genital sclerites important for insect taxonomists?

They serve as a valuable identification tool for distinguishing between different insect species.

What role do other sclerites play in insect reproduction?

Other sclerites, such as the subgenital plate and styli, facilitate mating or egg-laying.

aedeagus

male copulatory organ

claspers

specialized appendages found in male insects that are used to grasp females during mating

Grasshopper anatomy

subgenital plate

In males; located on bottom of aedeagus

styli

Peg-like appendages found along the sides of the abdomen in some very primitive insects like silverfish.

Pincers

In Dermaptera (earwigs), the cerci are heavily sclerotized and forceps-like. They are used mostly for defense, but also during courtship, and sometimes to help in folding the wings.

Median caudal filament

A thread-like projection arising from the center of the last abdominal segment (between the cerci). This structure is found only in 'primitive' orders (e.g. Diplura, Zygentoma, Ephemeroptera).

Cornicles

Paired secretory structures located dorsally on the abdomen of aphids. The cornicles produce substances that repel predators or elicit care-giving behavior by symbiotic ants.

Abdominal prolegs

Fleshy, locomotory appendages found only in the larvae of certain orders (notably Lepidoptera, but also Mecoptera and some Hymenoptera).

Sting

A modified ovipositor, found only in the females of aculeate Hymenoptera (ants, bees, and predatory wasps).

Abdominal gills

Respiratory organs found in the nymphs (naiads) of certain aquatic insects. In Ephemeroptera (mayflies), paired gills are located along the sides of each abdominal segment; in Odonata (damselflies), the gills are attached to the end of the abdomen.

Furcula

The 'springtail' jumping organ found in Collembola on the ventral side of the fifth abdominal segment. A clasp (the tenaculum) on the third abdominal segment holds the springtail in its 'cocked' position.

Collophore

A fleshy, peg-like structure found in Collembola on the ventral side of the first abdominal segment. It appears to maintain homeostasis by regulating absorption of water from the environment.

What are the only invertebrates that can fly?

Insects

How do insect wings develop?

As evaginations of the exoskeleton during morphogenesis.

When do insect wings become fully functional?

During the adult stage of an insect's life cycle.

What are the two main pairs of wings found on most insects?

One pair on the mesothorax and one pair on the metathorax.

True / False: Insects can have a pair of wings on the prothorax.

False (this never happens)

What are some adaptations of insect wings aside from flight?

protective covers (Coleoptera and Dermaptera), thermal collectors (Lepidoptera), gyroscopic stabilizers (Diptera), sound producers (Orthoptera), or visual cues for species recognition and sexual contact (Lepidoptera).

What runs throughout the wing tissue of insects?

A characteristic network of veins, extensions of the body's circulatory system

What do the veins in insect wings contain?

Hemolymph, a tracheal tube, and a nerve.

What is the function of veins in membranous wings?

To provide strength and reinforcement during flight.

Why are wing shape, texture, and venation important in insects?

They are distinctive among insect taxa and useful for identification.

What are some types of wing textures found in insects?

Membranous, parchment-like, heavily sclerotized, fringed with long hairs, or covered with scales.

Which insect orders are mentioned as having specific wing adaptations?

Coleoptera, Dermaptera, Lepidoptera, Diptera, and Orthoptera.

tegmen

The front wing of grasshoppers, crickets, katydids, and cockroaches

What is the function of the tegmen in insects?

It protects the hindwings when folded.

How does the tegmen contribute to insect behavior?

It plays a role in camouflage and displays, especially defensive displays.

What role does the tegmen play in sound production?

It is used as a soundboard by many insects, especially Orthoptera.