Insect Morphology

Exoskeleton Principal layers Epicuticle Cuticle Epidermis waxy layer provides waterproofing in/out delicate, may be scratched Cuticle chitinous, sometimes sclerotized layer Epidermis cellular layer the living “skin” with multiple secretory functions

Exoskeleton Protection from injury and disease Control of body fluids (preventing dessication and over-hydration) Support for muscles

Chitin Tough Flexible (not stretchable) Structurally cellulose-like Covers Entire body externally Digestive system (except midgut) Tracheae (except tracheoles)

Exoskeleton modifications Immovable projections wrinkles, spines – sound production, predation, etc. Movable projections Spurs, hairs/setae, scales – proprioception, external movement Invaginations Pits, grooves - indicate location of internal projections

Invaginations – Pits, Grooves

Directional definitions Anterior – toward the head Posterior – toward the tail (caudal) Dorsal – top or upper side Ventral – bottom or lower side Mesal – longitudinal centerline of dorsum or venter Axial – longitudinal axis of body Lateral – on side (pleural) Basal – near point of attachment (proximal) Apical – farthest from point of attachment (distal)

Body Regions Head – prostomium and 4 segments – sensation, ingestion Thorax – 3 segments – locomotion Abdomen – up to 12 segments – digestion, circulation, excretion, reproduction

Head Positions Hypognathous – mostly chewing herbivores/detritivores Prognathous – most predators Opisthognathous – sucking herbivores and predators

Head Regions Occiput Vertex Frons Clypeus Genae Ecdysial lines (frontal sutures + epicranial suture)

Sensing Organs Compound eyes or stemmata - mosaic vision Ocelli – phenology regulation? Antennae (scape, pedicel, flagellum) – touch, sound, smell

Mouthparts Labrum (“upper lip”) Mandibles (paired) Maxillae (paired) Lacinia Galea Palp Labium (“lower lip”) Submentum Mentum Glossae Paraglossae Palps Hypopharynx (“tongue”)

Thorax Alinotum = scutum + scutellum Pleuron Sternum

Leg Coxa Trochanter Femur Tibia Tarsus (subsegmented) Claw(s)

Wings

Abdomen Segments I–X visible in most insects Tergum Pleuron Sternum

Abdominal Appendages Respiratory structures – gills, siphon Cerci – tactile processes of abdominal segment XI Caudal filament – dorsal process of some mayflies Anal claws – caddisflies, some beetles Crochets – moths Genitalia – mating/oviposition structures of adults

Metamorphosis Ecologically similar larvae and adults “Ametabola” = Egg–larva–adult (“incomplete”) Collembola “Paurometabola” = Egg–larva–adult (“incomplete”) Orthoptera, Hemiptera Ecologically different larvae and adults “Hemimetabola” = Egg–larva–adult (“incomplete”) Ephemeroptera, Odonata, Plecoptera Holometabola = Egg–larva–pupa–adult (“complete”) Megaloptera, Neuroptera, Trichoptera, Lepidoptera, Mecoptera, Coleoptera, Diptera, Hymenoptera

Metamorphosis – Holometabola and “Hemimetabola”