Entomology Glossary

A

Abdomen

anatomy

The third and posterior section of an insect's body, containing the digestive and reproductive organs. Typically consists of 11 segments, though fewer are visible externally in many species.

Ametabolous

development

A type of development with no metamorphosis. The young resemble miniature adults and simply grow larger through successive moults. Found in silverfish and bristletails.

Antenna

anatomy

One of a pair of sensory appendages on the head of an insect, used for detecting odours, vibrations, humidity, and sometimes sound. Antennae come in many forms including filiform, serrate, pectinate, and plumose.

Aposematism

behaviour

Warning colouration that advertises an organism's toxicity, venomousness, or unpalatability to potential predators. Common examples include the bright yellow and black of wasps and the orange and black of monarch butterflies.

Apterous

morphology

Lacking wings. Some insects are naturally apterous (e.g. fleas, worker ants), while others have apterous forms within an otherwise winged species.

B

Binomial Nomenclature

taxonomy

The formal system of naming species using two Latin names: the genus name (capitalised) and the species epithet (lowercase), both italicised. Established by Carl Linnaeus in the 18th century.

Biological Control

ecology

The use of natural enemies (predators, parasitoids, or pathogens) to manage pest insect populations. Ladybirds controlling aphids is a classic example.

Bioluminescence

behaviour

The production of light by living organisms through a chemical reaction. In insects, bioluminescence is best known in fireflies (Lampyridae), where it is used for mate signalling.

Bivoltine

behaviour

Having two generations per year. Many temperate-region butterflies are bivoltine, with a spring and a summer generation.

Brachypterous

morphology

Having shortened or reduced wings that are not functional for flight. Some crickets and beetles have brachypterous forms.

C

Caste

behaviour

A specialised group within a social insect colony, defined by morphology and role. Typical castes include queens, workers, and soldiers. Found in ants, termites, and some bees and wasps.

Cercus

anatomy

One of a pair of appendages at the tip of the abdomen, often sensory in function. Cerci (plural) are prominent in earwigs, where they are modified into forceps-like pincers.

Chitin

anatomy

A tough, semi-transparent polysaccharide that forms the main component of the insect exoskeleton (cuticle). Chitin provides structural strength while remaining flexible at joints.

Chrysalis

development

The hard-shelled pupa of a butterfly. Unlike a cocoon, a chrysalis is not wrapped in silk but is the exposed pupal skin itself, often with gold or metallic markings.

Class

taxonomy

A major taxonomic rank below phylum and above order. All insects belong to class Insecta within the phylum Arthropoda.

Clavate

morphology

Club-shaped, gradually thickening towards the tip. Used to describe antennae (as in many beetles) or other body structures.

Cocoon

development

A silken case spun by the larva of many moths and some other insects, within which the pupa develops. The silk moth cocoon is the source of commercial silk.

Coleoptera

taxonomy

The order of beetles, the most species-rich order of insects with over 400,000 described species. Characterised by hardened forewings (elytra) that meet in a straight line down the back.

Commensalism

ecology

A relationship between two organisms in which one benefits while the other is neither helped nor harmed. Some insects live in ant nests without affecting the colony.

Complete Metamorphosis

development

A type of development (holometabolism) in which the insect passes through four distinct stages: egg, larva, pupa, and adult. Characteristic of beetles, butterflies, flies, and wasps.

Compound Eye

anatomy

An eye composed of many individual visual units called ommatidia. Dragonflies have the largest compound eyes, with up to 30,000 ommatidia per eye, providing nearly 360-degree vision.

Coxa

anatomy

The basal segment of an insect's leg, connecting the leg to the thorax. The coxa articulates with the body at the coxal cavity.

Critically Endangered

conservation

An IUCN Red List category indicating a species faces an extremely high risk of extinction in the wild. The most severe threat category before Extinct in the Wild.

Crypsis

behaviour

Camouflage — the ability of an insect to blend with its environment to avoid detection by predators or prey. Includes colouration, shape, and behaviour that match the surroundings.

Cuticle

anatomy

The non-cellular outer layer of the insect body, secreted by the epidermis. Composed primarily of chitin and proteins, it forms the exoskeleton and lines the foregut and hindgut.

D

Data Deficient

conservation

An IUCN Red List category for species where there is insufficient information to assess the risk of extinction. Many insect species fall into this category.

Detritivore

ecology

An organism that feeds on dead organic matter (detritus). Many beetles, fly larvae, and cockroaches are detritivores, playing a vital role in nutrient recycling.

Diapause

development

A period of suspended development triggered by environmental cues such as day length or temperature. Diapause allows insects to survive unfavourable seasons and is hormonally controlled.

Diptera

taxonomy

The order of true flies, characterised by having only one pair of functional wings. The hindwings are reduced to halteres used for balance. Includes mosquitoes, house flies, and hover flies.

Diurnal

behaviour

Active during the daytime. Most butterflies, many bees, and numerous flies are diurnal. Contrasts with nocturnal (night-active) and crepuscular (twilight-active).

E

Ecdysis

development

The process of shedding the old exoskeleton (moulting) to allow growth. Controlled by the hormone ecdysone. An insect is most vulnerable immediately after ecdysis, before the new cuticle hardens.

Eclosion

development

The emergence of an adult insect from the pupal case, or the hatching of a larva from the egg.

Ectoparasite

ecology

A parasite that lives on the outside of its host. Fleas, lice, and bed bugs are common ectoparasites of mammals and birds.

Elytra

anatomy

The hardened forewings of beetles (Coleoptera) that serve as protective covers for the membranous hindwings. Elytra are not used for flight but are lifted during takeoff to free the hindwings.

Endangered

conservation

An IUCN Red List category indicating a species faces a very high risk of extinction in the wild. Populations are declining rapidly due to habitat loss, pollution, or other threats.

Endoparasite

ecology

A parasite that lives inside the body of its host. Many parasitoid wasp larvae are endoparasites, developing within the bodies of caterpillars or other insects.

Entomology

taxonomy

The scientific study of insects. Derived from the Greek entomon (insect) and logos (study). Sub-disciplines include forensic entomology, medical entomology, and agricultural entomology.

Eusocial

behaviour

The highest level of social organisation, characterised by cooperative brood care, overlapping generations, and division of labour with reproductive and non-reproductive castes. Found in all ants, all termites, and some bees and wasps.

Exoskeleton

anatomy

The rigid external covering of an insect's body, composed of cuticle. It provides protection, prevents water loss, and serves as an attachment point for muscles. Must be shed (moulted) to allow growth.

Exuviae

development

The cast-off outer skin (exoskeleton) shed during moulting. Collecting exuviae is a common method for studying insect populations without harming living specimens.

F

Family

taxonomy

A taxonomic rank below order and above genus. Family names in zoology end in -idae. For example, Coccinellidae is the family of ladybirds.

Femur

anatomy

The third segment of an insect's leg, typically the largest and most muscular. In grasshoppers and crickets, the hind femora are greatly enlarged for jumping.

Filiform

morphology

Thread-like and of uniform width throughout. Used to describe antennae, as in many ground beetles and cockroaches.

G

Ganglion

anatomy

A cluster of nerve cell bodies forming a nerve centre. Insects have a chain of ganglia running along the ventral side of the body, with the largest (the brain) in the head.

Genus

taxonomy

A taxonomic rank below family and above species. The first part of an organism's binomial name. For example, in Apis mellifera (honeybee), Apis is the genus.

H

Haemolymph

anatomy

The fluid that circulates in the open circulatory system of insects, analogous to blood. It transports nutrients and waste but does not carry oxygen (except in some aquatic insect larvae).

Haltere

anatomy

One of a pair of small, club-shaped structures in flies (Diptera) that are modified hindwings. Halteres vibrate during flight and function as gyroscopic balancing organs.

Hemimetabolous

development

Undergoing incomplete metamorphosis with three life stages: egg, nymph, and adult. The nymph gradually acquires adult features through successive moults.

Hemiptera

taxonomy

The order of true bugs, characterised by piercing-sucking mouthparts and often partly thickened forewings. Includes shield bugs, cicadas, aphids, and bed bugs.

Herbivore

ecology

An organism that feeds on plants. The majority of insects are herbivores, feeding on leaves, stems, roots, flowers, fruits, seeds, or sap.

Holometabolous

development

Undergoing complete metamorphosis with four life stages: egg, larva, pupa, and adult. About 85%% of all insect species are holometabolous.

Holotype

taxonomy

The single specimen designated as the name-bearing type of a species when it is first scientifically described. Holotypes are preserved in museum collections.

Hymenoptera

taxonomy

The order containing ants, bees, wasps, and sawflies. Many species are social. This order includes the most important insect pollinators and many parasitoids used in biological control.

I

Imago

development

The adult, sexually mature stage of an insect. The final stage of metamorphosis, following the pupa in holometabolous insects or the final nymphal instar in hemimetabolous insects.

Incomplete Metamorphosis

development

A type of development (hemimetabolism) in which the insect passes through three stages: egg, nymph, and adult. The nymph resembles a small adult and moults several times. Found in grasshoppers, bugs, and dragonflies.

Inquiline

ecology

An organism that lives in the nest or dwelling of another species, often exploiting food or shelter without directly harming the host. Some beetles and flies are inquilines in ant or termite nests.

Instar

development

The developmental stage of an insect between two successive moults. The first instar is the stage immediately after hatching; subsequent instars follow each moult.

L

Labium

anatomy

The lower lip of the insect mouthparts, formed by the fusion of the second pair of maxillae. In dragonfly nymphs, the labium is modified into an extendable prehensile organ for catching prey.

Labrum

anatomy

The upper lip of the insect mouthparts, a movable flap covering the mandibles from above. It helps to manipulate food during feeding.

Lamellate

morphology

Having plate-like or leaf-like segments at the tip. Used to describe antennae of scarab beetles, where the terminal segments fan out.

Larva

development

The immature, feeding stage of a holometabolous insect, typically worm-like and differing markedly from the adult form. Examples include caterpillars (Lepidoptera), grubs (Coleoptera), and maggots (Diptera).

Least Concern

conservation

An IUCN Red List category for species that are widespread, abundant, and not currently at significant risk of extinction.

Lepidoptera

taxonomy

The order of butterflies and moths, characterised by wings covered in tiny overlapping scales. The second-largest insect order with about 180,000 species.

M

Macropterous

morphology

Having fully developed wings capable of flight. The winged form in species that show wing polymorphism.

Mandible

anatomy

One of the paired, jaw-like mouthparts of an insect used for biting, cutting, and crushing food. Mandibles move laterally (side to side) rather than vertically.

Maxilla

anatomy

One of the paired mouthparts behind the mandibles, bearing a sensory palp. Maxillae help manipulate and taste food. In butterflies, the maxillae are modified into the coiled proboscis.

Mesothorax

anatomy

The second (middle) segment of the thorax, bearing the forewings and second pair of legs.

Metathorax

anatomy

The third and most posterior segment of the thorax, bearing the hindwings and third pair of legs.

Mimicry

behaviour

The resemblance of one species to another for protective advantage. Batesian mimicry involves a harmless species imitating a harmful one. Muellerian mimicry involves two harmful species resembling each other.

Moult

development

The process of shedding and replacing the exoskeleton to allow growth. Also called ecdysis. The discarded exoskeleton is called an exuviae.

Multivoltine

behaviour

Having more than two generations per year. Common in tropical insects and pest species such as aphids, which can produce many generations in a single season.

Mutualism

ecology

A symbiotic relationship in which both organisms benefit. Pollination is a classic example: the insect gets food (nectar/pollen) and the plant gets its pollen transferred.

Myrmecophily

ecology

An association between an organism and ants. Many insects (beetles, butterflies, crickets) have evolved to live in ant nests, sometimes as parasites, sometimes as mutualists.

N

Near Threatened

conservation

An IUCN Red List category for species that are close to qualifying for a threatened category, or likely to qualify in the near future.

Nocturnal

behaviour

Active during the night. Most moths, many beetles, and various cockroaches are nocturnal. Many nocturnal insects are attracted to artificial light sources.

Nymph

development

The immature stage of a hemimetabolous insect. Nymphs resemble small adults but lack fully developed wings and reproductive organs. They grow through successive moults.

O

Ocellus

anatomy

A simple eye found on the top of the head of many insects, usually occurring in a group of three. Ocelli detect light intensity and are thought to aid in flight stability, but do not form images.

Odonata

taxonomy

The order of dragonflies and damselflies, ancient predatory insects with large compound eyes and two pairs of strong, transparent wings. Among the fastest flying insects.

Order

taxonomy

A major taxonomic rank below class and above family. There are approximately 30 recognised orders of insects, including Coleoptera, Lepidoptera, Diptera, and Hymenoptera.

Orthoptera

taxonomy

The order of grasshoppers, crickets, and katydids. Characterised by enlarged hind legs for jumping and the ability to produce sound through stridulation.

Ovipositor

anatomy

A tubular organ at the end of the female abdomen used to deposit eggs. In some species (such as parasitic wasps), it is long and needle-like for penetrating plant tissue or host insects. In bees and wasps, it is modified into a stinger.

P

Palp

anatomy

A segmented, finger-like sensory appendage associated with the maxillae or labium. Palps are used for tasting and touching food before ingestion.

Parasitoid

ecology

An organism that develops in or on a host organism, eventually killing it. Parasitoid wasps and flies lay eggs in or on host insects; the larvae consume the host as they develop.

Pectinate

morphology

Having comb-like branches or teeth. Used to describe antennae with lateral projections, as in many moths and some beetles.

Pheromone

behaviour

A chemical substance released by an insect that triggers a response in others of the same species. Types include sex pheromones (mate attraction), alarm pheromones (danger signals), and trail pheromones (foraging paths).

Phylum

taxonomy

The highest major taxonomic rank within a kingdom. All insects belong to phylum Arthropoda, along with arachnids, crustaceans, and myriapods.

Plumose

morphology

Feather-like, with fine branches. Used to describe antennae with whorls of fine hairs, as in male mosquitoes and midges.

Pollinator

ecology

An animal that transfers pollen from the male parts of a flower to the female parts, enabling fertilisation. Key insect pollinators include bees, butterflies, moths, flies, and beetles.

Pollinator Decline

conservation

The observed worldwide reduction in pollinator populations, driven by habitat loss, pesticide use, disease, climate change, and invasive species. A major concern for global food security.

Predator

ecology

An organism that hunts and kills other organisms for food. Insect predators include dragonflies, ladybirds, praying mantises, and many beetles and wasps.

Proboscis

anatomy

A tubular, often coiled mouthpart used for feeding on liquids. Found in butterflies, moths, and some flies. In butterflies, it uncoils to reach nectar deep within flowers.

Pronotum

anatomy

The dorsal plate of the prothorax (first thoracic segment). In beetles, the pronotum is particularly prominent and forms a shield-like covering.

Prothorax

anatomy

The first segment of the thorax, bearing the first pair of legs but no wings. In praying mantises, the prothorax is elongated, giving them their characteristic appearance.

Pupa

development

The non-feeding, transformation stage between larva and adult in holometabolous insects. During this stage, larval tissues are reorganised into the adult body plan.

R

Red List

conservation

The IUCN Red List of Threatened Species, the world's most comprehensive inventory of the conservation status of biological species. Uses standardised criteria to assess extinction risk.

S

Saprophage

ecology

An organism that feeds on dead or decaying organic matter. Many fly larvae (maggots) and beetle larvae are saprophages essential for decomposition.

Scutellum

anatomy

A triangular plate on the dorsal surface of the thorax, visible between the bases of the wings. Particularly prominent in shield bugs (Pentatomidae).

Serrate

morphology

Having saw-like teeth or notches along the edge. Used to describe antennae with triangular, tooth-like segments, as in some click beetles.

Setose

morphology

Covered with bristle-like structures (setae). Many caterpillars are densely setose as a defence against predators.

Species

taxonomy

The fundamental unit of biological classification. Members of a species can interbreed to produce fertile offspring. The second part of the binomial name (e.g. mellifera in Apis mellifera).

Spiracle

anatomy

An external opening of the tracheal (breathing) system, typically found along the sides of the thorax and abdomen. Spiracles can be opened and closed to regulate gas exchange and water loss.

Stridulation

behaviour

The production of sound by rubbing two body parts together. Crickets stridulate by rubbing the forewings together; grasshoppers rub the hind leg against the forewing.

Symbiosis

ecology

A close and prolonged interaction between two different species. Includes mutualism (both benefit), commensalism (one benefits), and parasitism (one benefits at the other's expense).

T

Tarsus

anatomy

The foot of an insect, consisting of one to five segments. The terminal segment typically bears claws, and often adhesive pads that allow insects to walk on smooth surfaces.

Thanatosis

behaviour

The behaviour of feigning death (playing dead) to avoid predation. Many beetles, weevils, and some caterpillars exhibit thanatosis when disturbed.

Thermoregulation

behaviour

The ability to control body temperature through behaviour (e.g. basking, shivering flight muscles) or physiology. Honeybees can collectively regulate hive temperature to within 1 degree C.

Thorax

anatomy

The middle section of the insect body, between the head and abdomen. Divided into three segments (prothorax, mesothorax, metathorax), it bears the legs and wings.

Tibia

anatomy

The fourth segment of an insect's leg, between the femur and the tarsus. In bees, the hind tibia has a pollen basket (corbicula) for transporting pollen.

Trachea

anatomy

A tube of the respiratory system that carries air directly to the tissues. The tracheal system branches into increasingly fine tubes (tracheoles) that reach every cell.

Trochanter

anatomy

The second segment of an insect's leg, a small segment between the coxa and the femur.

Trophallaxis

behaviour

The exchange of food between members of a social insect colony, either mouth-to-mouth or anus-to-mouth. A key mechanism for distributing nutrients and chemical signals within ant and termite colonies.

Tympanum

anatomy

A vibrating membrane that functions as an ear. Found on the legs of crickets and katydids, or on the abdomen of grasshoppers, moths, and cicadas.

U

Univoltine

behaviour

Having one generation per year. Many insects in temperate and cold climates are univoltine, synchronising their life cycle with seasonal conditions.

V

Vector

ecology

An organism that transmits a pathogen from one host to another. Mosquitoes are vectors for malaria, dengue, and Zika; tsetse flies vector sleeping sickness.

Vulnerable

conservation

An IUCN Red List category indicating a species faces a high risk of extinction in the medium-term future. Less critical than Endangered but still of serious concern.