Entomological Terms    

The following is a list of terms you will find useful in using the keys in the book to identify your
insects. Yes, you will have some quizzes asking you the meaning of some of these terms as well!

Insects are hexapodous – that is, they have six legs (on the thorax)
The insect body has three regions: Head, thorax, and abdomen
All regions are segmented:
    Head has 4 or 5 segments plus prostomium (unsegmented part of body in front of mouth)
    Thorax has three segments: pro-, meso- and metathorax
        Each segment has a pair of legs; the meso- & metathorax often each have a pair of wings
    Abdomen: Typically has 11 segments, though 10 usually visible; some hexapods have fewer

Directional terms
    Anterior or cephalad – toward the front or head
    Posterior or caudad – toward the rear or tail
    Dorsal – toward the back or top (upperside) in the case of insects
    Ventral – toward the belly or underside in the case of insects
    Lateral – toward the sides
    Medial -- toward the middle/midline of the body+
    Proximal (basal) – toward the base; for wings/legs, proximal is near the thorax
    Distal (apical) – toward the tip; for wings/legs, distal is near the tip of the wing/leg
    Longitudinal – along the body
    Transverse – across the body
    External – toward the outside
    Internal – toward the inside
    Porrect – pointing directly forward

Exoskeleton or Cuticle
    General Terms
        Epicuticle: Outer portion of cuticle
        Procuticle: The rest of the cuticle
        Chitin: An important nitrogen containing protein in the cuticle
        Intersegmental folds/grooves: Grooves between body segments; cuticle often thin here to
            allow for movement.
        Suture: A groove, typically between sclerites (see below)
        Stria: A simple “decorative” groove; seen typically on the elytra of beetles
        Apodemes, apophyses, phragmata: These are various indentations in the cuticle that are used
            for muscle attachment internally
    Sclerites – the harden “pieces” that make up the exoskeleton (cuticle)
        Tergite: dorsal sclerite; sclerite on the top -- Notum: tergite in the thoracic region            
        Pleurite: lateral sclerite; sclerite on the side
        Sternite: ventral sclerite, sclerite on the bottom
    Hairs and spines
        Trich-: a prefix meaning “hair”
        Chaetotaxy: the study of the patterns of hairs on an insect
        Setae: hairs
        Sensillum: a simple sense organ, often a hair used to detect movement (like your hairs)
            Vibrissa – a sensory hair around the mouth; Arista – a large bristle at the end of antennae
        Style: any sharply pointed organ; a spine, typically sticking off the cuticle

    General Terms
        Occiput: Back of the head
        Vertex: Top of the head
        Frons: Top of face between the eyes
        Clypeus: middle of face above labrum
        Gena: side of face; “cheek”
        Labrum: upper lip, just above mouthparts
        Gula: underside of “chin”
    Mouthparts are three-parted (each representing one of the head sements):
        Mandible (anterior), Maxilla, Labium (posterior)
            Spinneret: specialized organ of mouthparts for spinning silk
        Palps: extensions off of the mouthparts (none on mandible)
        Proboscis/Rostrum: highly modified, tubular mouthparts for sucking
    Position of mouthparts 
        Entognathous: mouthparts are retracted into a pouch
        Exognahthous: mouthparts visible and extending out from head; not retractable
            Prognathous: mouthparts pointing anteriorly
            Hypognathous: mouthparts point downward
            Opisthognathous: mouthparts pointing posteriorly
        Scape: basal segment of an antenna
        Pedicel: segment above the scape
        Flagellum: many segmented region of the antenna distal to the pedicel
        Ocellus: simple eye, often located on the face below or between the larger compound eyes
        Compound eye: complex eye for forming images; made up of several separate ommatidia

Thorax – pro-, meso- and metathorax (the three segments)
    General Terms
        Notum: top of thorax; thoracic tergites; divided into scutum (anterior) and scutellum (post.)
        Thoracic pleurites divided into the episternite (anterior) and epimeron (posterior)
    True Legs – one pair on each thoracic segment; several parts:
        Meron, Coxa, trochanter, femur, tibia, tarsus (with several separate segments called
            tarsomeres), pretarsus (includes claws and pulvillus/arolium)
        Pulvillus/Arolium: padlike structures between claws used for gripping on smooth surface
    Wings – typically two pair (not always) on the meso- and metathorax
        -pter-: prefix or suffix meaning “wing”
        Apterous: without wings
        Brachypterous: with very reduced wings
        Alate (or pterous): fully winged
        Veins of wings – from anterior to posterior edge:
            Costa, subcosta, radius, median, cubitus, anal
        Cell: a region of the wing surrounded by veins
            Basal cell: near base of wing; Discal cell: in the middle of the wing
        Tegula -- a sclerite at leading edge of base of wing, can be expanded back over wing base
        Elytra -- hard forewing; as in beetles
        Tegmen -- leathery forewing; as in grasshoppers
            Humeral region: anterior base of the wing
            Costal region: the leading edge of the wing
            Apical region: the tip of the wing
            Median region: the center of the wing
            Anal region: the trailing (back) edge of the wing

Abdomen – Typically 11 segments; though (only) 10 often visible
    General Terms
        Cercus: an appendage (hair, style, spine, claw) of the last (terminal) abdominal segment
        Cloaca: a common opening for the digestive and reproductive systems
        Paraprocts: lateral sclerites of last abdominal segment
        Prolegs, with crochets: on some abdominal segments on some larvae, used for locomotion
    Reproductive structures – typically associated with abdominal segments 8 & 9
        Aedeagus: penis (male)
        Ovipositor: Egg laying structure in female

Internal Body systems
        Spiracles: openings to outside, found on various thoracic and abdominal segments
        Tracheae: passageways inside the spiracles allowing air to pass throughout the body
        Tracheoles: smaller passageways reaching virtually every stationary cell in the body
    Circulatory – insects have an open system; “blood” bathes body tissues
        Hemolymph: insect “blood”
        Heart is located in abdomen; has ostia: openings to the body cavity to receive blood
        Aorta: the main blood vessel; carries blood anteriorly from heart
    Excretory: Malphighian Tubules are the internal excretory organs of insects
        Spermatophore: a capsule containing sperm; released by male into female
        Spermatheca: internal sac that receives sperm/spermatophore (bursa copulatrix in Lepidoptera)
        Ootheca: a capsule secreted by some female insects around the eggs for protection
    Digestive: Foregut (Stomodaeum), Midgut, Hindgut
        Brain, with ventral nerve cord; several large ganglia (control centers outside brain)

    General Terms
        Metamorphosis: changing body form through development
        Ametabolous: development without metamorphosis; what hatches from egg is a small version
            of the adult
        Hemimetabolous: development by incomplete metamorphosis; what hatches from egg looks
            like adults but lacks wings; wings get progressively bigger with each molt

        Holometabolous: development by complete metamorphosis (egg, larva, pupa, adult).
        Apterygotes: insects with no wings; ametabolous
        Exopterygotes: insects with external wing development; hemimetabolous
        Engopterygotes: insects with internal wing development; holometabolous
        Ecdysis: molting
        Teneral: recently molted individual; the exoskeleton is not hardened at this time
        Stadium, Instar: stadium - any stage between molts; instar - stages between molts in larvae
        Eclose: to emerge (hatch), typically from an egg or pupa
        Imaginal disks (anlage): a piece of tissue inside an immature stage that will grow into an adult
            structure; imaginal refers to the imago (adult) stage
    Egg: Has a chorion (egg shell)
    Nymph: immature hemimetabolous insect
        Naiad: an aquatic nymph
    Larva: in the strictest sense, this is an immature holometabolous insect
        Instar: a larval stadium; typically, a larva will pass through several instars
            ultimate instar – last larval stage; penultimate instar – next to last larval stage
        Vermiform: shaped like a worm
        Eruciform: shaped like a caterpillar
            Has prolegs on abdominal segments (not true legs), with minute hooks (crochets)
    Pupa: the stadium between larval and adult stages of holometabolous insects
        Chrysalis: a naked pupa
        Cocoon: a silken case woven around a pupa
        Decticious: a pupa having movable mouthparts
        Adecticious: a pupa having non-movable mouthparts
        Exarate: a pupa having movable appendages
        Obtect: a pupa with appendages appressed to the pupa (not free moving)
        Exuvium: a shed pupal skin
    Imago: the adult stadium; typically, the only stage with functional wings
    Parthenogenesis: a form of asexual reproduction in which females lay single sex eggs
        Arrhenotoky – only males produced; Thelytoky – only females produced

Mode of Life/Movement
    Cursorial: adapted for running
    Saltatorial: adapted for jumping
    Arboreal: adapted for living in the trees
    Fossorial: adapted for digging
    Natatorial: adapted for swimming
    Raptorial: adapted for grasping (a Praying Mantis’ forelegs, for instance)