Claire Weiss' Online Dicotomous Insect Identification Key


Below is a glossary of insect morphology terms.  Click on linked words for illustrations.

Abdomen:  Third and last section of the insect's body, usually having 10 segments:

Antenna (pl. antennae): Appendages on the head of the insect, usually paired and segmented.  Antennae are made up of three basic segments:  the scape, pedicel, and flagellum which is in turn made up of multiple flagellomeres.  Antennae come in various forms depending on how the insect uses them.  These different forms are often very useful in identifying insects.  They include:

Setaceaous (bristled) Filiform (threadlike)
Moniliform ("beaded") Serrate (sawlike)
Pectinate (comblike) Clubbed (clubbed)
Geniculate (elbowed) Plumose (feathery)
Aristate (bulbous with a filament) Stylate (stylated)
from Borror, Donald et al., 1992

Abdominal appendages:  Either filaments or cerci.  Abdominal filaments are thread-like processes located at the end of the abdomen.  Cerci are shorter, usually scleritized appendages of the last segment of the abdomen.

Haltere (pl. halteres):  Modified wing structure resembling knobs.  Found in the place of the hind wings in Diptera and forewings in Strepsiptera.  Function as gyroscopic instruments in flight:

Haustellate:  Sucking.  refer to "mouthparts"

Head:  First section of the insect's body:

Hypognathous:  Mouthparts directed downward toward the ground.  Used for grazing:


Mandibulate:  Chewing.  refer to "mouthparts"


Mandibulate: "Chewing" mouthparts.  Scleritized mandibles ('jaws') which move side to side for biting and chewing food particles.
Haustellate:  "Sucking" mouthparts.  Often form tubular structures including beaks, probosces, and rostra:
Proboscis Rostrum

Opisthognathous:  Mouthparts that are directed backward below the insect's body:


Prognathous:  Mouthparts that are directed forward infront of the insect:


Scleritization:  Hardening of insect exoskeleton to make a strong, armor-like 'skin'.

Tarsus (pl. tarsi):  Last section of insect legs which are made up of several segments called tarsomeres. (see below)

Tarsomere (pl. tarsomeres):  Segments of the tarsus:

(Snodgrass, 1995)

Thorax:  Middle section of the insect's body, having three segments consisting of the prothorax, mesothorax, and metathorax.  The prothorax holds the front pair of legs.  The mesothorax holds the second pair of legs and the front pair of wings.  The metathorax holds the third pair of legs and the hind wings.

Wings:  Appendages used for flight.  Insects with wings have either one or two pair.  If a second pair is absent, halteres are often in the place of the missing pair (refer to halteres).  Wings may be membranous or scleritized.  Scleritized wings may be in the form protective elytra (in coleoptera) or tegmina (in orthoptera).  The scleritized forewing covers the membranous hind wing and protects it from undue wear and tear.  Membranous wings are usually highly veined with membrane between (hence 'membranous'), although the membrane may be covered with scales as in butterflies (lepidoptera).


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