External Morphology of Insects

Tagmosis

The formation of specialized body segments in arthrpods.

Head

Anterior-most tagma of an insect, crucial for food ingestion and sensing the environment.

Thorax

Middle tagma of an insect, between the head and abdomen, primary purpose is for locomotion

Abdomen

Posterior-most tagma of an insect, houses digestive canal, doral blood vessel, & reproductive organs, made of 11 segments

Integument

The tough, outer body layer of an insect. The largest organ of insects, very diverse in structure, and critical to their success.

Cuticle

The outermost layer of an insect’s integument, the exoskeleton.

Epidermis

A deep, single layer of cells, innermost layer of an insect’s integument.

Sclerites

Rigid, discrete plates making up an insect’s cuticle.

Setae

Hair-like projections on an insect’s integument.

Spines

Rigid outgrowths of an insect’s integument.

Spurs

Movable outgrowths of an insect’s integument

Sutures

Grooves on the surface of an insect’s integument that separate sclerites

Hypognathous

Directional position of the head where mouthparts are directed downward, below the eyes

Prognathous

Directional position of the head where mouthparts are directed forward, anterior to the eyes

Opisthognathus

Directional position of the head where mouthparts are directed posteriorly, beneath the thorax

Cervix

A membranous neck region of the head

Cervical sclerites

Lateral plates of cervix that help move the head

Compound eyes

Large pairs of sensory organs composed of many ommatidia

Ommatidia

Individual light-processing units that comprise insect’s compound eyes

Vertex

Dorsal section of head, between eyes

Gena

The area ventral to the vertex and compound eyes, may not be visually distinct

Antennae

Paired, segmented sensory structures on an insects head, main function is sensory. May be more elaborate in males and have additional sensory capacity

Frons

Ventral to the vertex, between eyes and antennae

Clypeus

Area of an insect’s head ventral to the frons

Ocelli

Simple eyes located between compound eyes

Tentorium

A special modification of the head, serves as a site for muscle attachments and also stabilized the head.

Scape

Basal-most section of an insect’s antennae

Pedicel

Middle section of an insect’s antennae

Flagellum

Distal-most segment of an insect’s antennae, often multi-segmented into flagellomeres

Sensilla

Sensory receptors on the antennae, pegs, cones, pits, or hairs. Sense heat, chemicals, moisture, and movement

Filiform

Antennal type that is thread-like with segments nearly uniform in size, often cylindrical

Setaceous

Antennae type that are bristle-like, segments becoming more slender distally

Moniliform

Antennae type with bead-like spherical segments similar in size

Clavate

Antennae type where segments increase gradually in size distally

Capitate

Antennae types where segments increase suddenly in size distally

Serrate

Antennae type that are saw-like, with triangular segments, especially in distal 2/3

Stylate

Antennae type with distal-most segment having an elongate finger-like process

Pectinate

Antennae type that are comb-like and have long lateral processes

Geniculate

Antennae type that are elbowed, with the scape long, and the pedicel small and at an angle to the scape

Lamellate

Antennae type with the terminal segments expanded laterally to form rounded or oval plate-like lobes

Plumose

Antennae type that are feathery, most segments have whorls of long hair

Aristate

Antennae type with the last segment enlarged, with a dorsal bristle

Mouthparts

modified, paired appendages used to capture, manipulate, gather, chew food

Labrum

Anterior-most segment of mouthparts, “upper lip”

Mandibles

Paired, heavily-sclerotized jaws, used to cut & crush food and used for defense

Molar area

Section of mandibles modified for biting and often hardened with metal deposits

Maxillae

Smaller pair of jaws that assist mandibles in processing

Cardo

Basal sclerite of maxilla

Stipes

Distal sclerite of maxilla

Lacinia

Distal pointed lobe of maxilla

Galea

Distal rounded lobe of maxilla

Labium

Posterior-most section of mouthparts, “lower lip”, similar to maxillae but not paired

Postmentum

Basal section of labium

Prementum

Distal section of labium, with glossae, paraglossae, and palps

Glossae

Small pair of distal, inner lobes on prementum of labium

Paraglossae

Large pair of distal, outer lobes on prementum of labium

Palps

Antennae-like segmented appendages on the maxillae and labium, help manipulate food into mouth and sense food

Hypopharynx

A tongue-like structure in chewing insects, variously modified and often secreting saliva

Entognathous

Of arthropods whose mandibles and maxillae are withdrawn into the head capsule when not in use, 6-legged arthropods like Collembola, Diplura, Protura

Ectognathous

Of arthropods whose mouthparts are visible and not withdrawn into the head capsule, typical of “true” insects

Chewing mouthparts

Most adult and immature insects have these, least specialized & basic type, for solid food

Cutting-sponging mouthparts

Extremely specialized mouthparts seen in a few species of adult flies, parasitic blood-feeders of vertebrates. Mandibles and maxillae are long and pointed to pierce skin and labium sponges up blood

Sponging mouthparts

Specialized group of flies (house flies), proboscis formed of mostly labium, maxillae and mandibles largely lost (maxillary palps remain), sponging labellum at tip of proboscis sponges up liquid food, hypopharynx secretes saliva to liquefy solids

Siphoning mouthparts

Seen in butterflies & moths, long proboscis formed from galea take up water and nectar and is coiled under head when not in use, mandibles are reduced or lost, between galea is a food canal that siphons up food using sucking pump in head

Piercing-sucking mouthparts

Second-most common mouthparts, have independently evolved in distantly related groups, used to suck blood or plant nectar, elongate beak composed of long needle-like stylets

Stylets

Specialized maxillae and mandibles to be long and needle-like in piercing-sucking mouthparts, enter animal or plant tissue, may have two channels for food and saliva

Sheath

Specialized labium in piercing-sucking mouthparts, does not enter animal/plant tissue but guides and cradles stylets

Chewing-lapping mouthparts

Used in adult bees to take up nectar and honey, proboscis formed by glossae of labium and galea of maxillae, nectar is drawn in by a sucking pump in head and movement of proboscis. Mandibles are used for nest-building, feeding queen, grooming, fighting

Prothorax

Anterior-most segment of thorax, attachment point for first pair of legs

Mesothorax

Middle segment of thorax, attachment point for second pair of legs and forewings

Metathorax

Posterior-most segment of thorax, attachment point for third pair of legs and hindwings

Pronotum

Dorsal portion of prothorax, often enlarged in treehoppers & cockroaches

Mesonotum

Dorsal portion of mesothorax

Metanotum

Dorsal portion of metathorax

Propleuron

Lateral wall of prothorax

Mesopleuron

Lateral wall of mesothorax

Metapleuron

Lateral wall of metathorax

Prosternum

Ventral plate of prothorax

Mesosternum

Ventral plate of mesothorax

Metasternum

Ventral plate of metathorax

Pleural suture

Suture that divides pleuron into two areas, extending from wing to leg

Episternum

Pleural area anterior to the pleural suture

Epimeron

Pleural area posterior to the pleural suture

Scutellum

Posterior dorsal sclerite, often present on meso- and metathorax

Legs

Paired appendages of the thoracic segments, modified for various functions in different insect groups

Coxa

Basal-most segment of the leg

Trochanter

Second-most basal segment of the leg

Femur

Middle segment of the leg, may have long spines or spurs

Tibia

Second-most distal segment of the leg, may have long spines or spurs

Tarsus

Distal-most segment of the leg

Tarsomeres

Up to five sub-segments of the tarsus

Tarsal formula

Number of tarsomeres in each insect leg, useful for identifying beetles

Cursorial

Leg modification for running & walking

Raptorial

Leg modification for catching prey

Saltatorial

Leg modification for jumping

Natatorial

Leg modification for swimming

Fossorial

Leg modification for digging

Prehensile

Leg modification for grasping & holding onto

Corbiculum

Modification on hind tibia of worker honeybees, “pollen basket”, depression fringed by long stiff setae

Wings

Flap-like cuticular projections supported by tubular veins, found on meso- and metathorax, contain tracheae (air vessels), blood vessels, and nerves