Hexapoda

Sub-Phylum: Hexapoda

Characteristics
- Insects possess a unique body structure divided into three parts: head, thorax, and abdomen.
- They have three pairs of legs (total of six legs), facilitating their locomotion.
- Most insects have two pairs of wings, located in the thoracic region, though some groups have lost this trait.
- A pair of antennae and compound eyes are essential sensory organs.
- Their body is encased in a thickened cuticle, known as sclerites, connected by softer areas called sutures.
- Insects utilize spiracles and a tracheal system for gas exchange.
- Other shared characteristics with arthropods are also relevant.

Insects are highly diverse and abundant, thriving in all habitats except sub-tidal marine environments.
Over 1 million species described, illustrating their evolutionary success on land and flight adaptations.
They play crucial roles as:
- Prey and predators in ecosystems.
- Bioturbators in soil and marine environments.
- Decomposers integral to nutrient cycling.
- Pollinators of the majority of crops globally.
While beneficial, some are pests, impacting agriculture, and can be vectors for diseases.

Subphylum Hexapoda
- Entognatha: Small, wingless insects with hidden mouthparts, lacking spiracles, and tracheae; e.g. springtails (<1% of Hexapoda).
- Class Insecta: Characterized by exposed mouth appendages and well-developed Malpighian tubules, many species exhibit flying capabilities across 30 orders.

Main Body Parts:
- Head
- Thorax
- Abdomen
- Structure includes various wings and appendages, such as forewings, hindwings, and specialized mouthparts.
- Key features: compound eyes, antennae, mandibles, and specialized sensory organs.

Insects have an exoskeleton, providing protection and support, essential for adapting to terrestrial life.
Strong and efficient appendages enhance mobility and aid in flight.
Adaptations like a waxy cuticle and specialized gas-exchange structures prevent desiccation and support life in various environments.

Legs are adapted to lift the body for effective locomotion. Movement occurs in an alternating tripod sequence to maintain balance.
Specific insects, like water striders, utilize surface tension for movement on water.

Insects with wings demonstrate true flight capabilities, often with two pairs of wings.
The wing structure includes thin cuticular membranes and veins filled with hemolymph.
Wing movement requires significant energy expenditure, with some species achieving hundreds of wing beats per second.

Insects exhibit diverse feeding strategies, allowing resource utilization across environments.
Categories:
1. Biters-Chewers: Includes orthopterans; possess well-developed mandibles.
2. Suckers: Modified mouthparts for extracting liquids from plants or animals; e.g., butterflies.
3. Spongers: Use capillary action to feed on liquids, with some digestion occurring externally.

Insects possess a dorsal tubular heart and a unique blood system for nutrient and waste exchange. Gas exchange occurs through tracheal systems or the body surface, facilitated by spiracles.

Land insects evolved Malpighian tubules for water balance and nutrient reabsorption. Nitrogenous waste is primarily in the form of uric acid.

Insects demonstrate a highly developed nervous system with sensory adaptations such as compound eyes for various wavelengths of light, including UV capture.
Microscopic sensilla on various body parts enhance tactile and chemosensory perception.

Most insects are dioecious, displaying sexual dimorphism and complex mating behaviors.
Internal fertilization and egg-laying are common, with some species exhibiting live birth.

Ametabolous: Juveniles resemble mini adults and grow through moulting.
Hemimetabolous: Nymphs transition into winged adults with intermediate stages.
Holometabolous: Includes caterpillars and pupae, leading to transformation into adult forms.

Largest insect order, found in diverse habitats globally, significant as pests and recyclers.
Historical and cultural significance of beetles, such as the scarab in ancient Egypt.

Includes diverse species with substantial ecological roles, including pollination and decomposition.
Remarkable adaptations in flight and larvae to extreme environments.

Economically and ecologically important for their beauty but also destructive to crops. Migration patterns have significant biological and conservation implications.

Noteworthy for social systems and interactions within ecosystems as pollinators and pest controllers.

Includes significant agricultural pests and species with unique feeding adaptations affecting plant health.

Known for their acoustic communication and ecological impacts on agriculture. Increased interest in sustainable consumption of crickets and locusts.

Fleas play critical roles as pests and disease vectors in mammals, exhibiting diverse adaptations for life as bloodsuckers.

Exploration of the medical and ecological roles of insects through studies and historical context.
Increasing interest in the intersection of human health, agriculture, and insect populations.