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Insect Glossary

AbdomenThe abdomen is the third of an insect’s three main body parts. The three body parts from front to back are: the head, the thorax and the abdomen. An insect’s reproductive structures arise from the abdomen.

Silverfish with caudal filaments
The three caudal filaments are visible at the rear of the insect (they are the “tails” at top of the photo). The two outer filaments are known as cerci, and the central filament is simply called a caudal filament (or median caudal filament). Caudal filaments may be thin, as they are here, or may be more robust, even pincer-like, as they are in earwigs. Photo credit: Sebastian Stabinger.

Caudal filamentA caudal filament is a projection that extends from an insect’s abdomen as if the insect has a tail. Depending on the species, an insect may possess up to three caudal filaments, or none at all. The cerci are types of caudal filaments.

CerciThe cerci are a pair of caudal filaments that occur in some insects. Depending on the insect, they may be short, long, thin, robust or pincer-like. Some insects possess a third median caudal filament that is located between the two cerci.

Chewing mouthpartsInsects with chewing mouthparts have a pair of mandibles, one on each side of the head. The mandibles move from side to side. Chewing mandibles come in many different sizes and shapes. For instance, some insect mandibles are broad and flat — similar a person’s incisors — and are good for shearing. Some chewing mandibles are long and narrow with jagged edges — rather like pinking shears — and are good for crushing.

ClawsThe claws are located on the tip of the last segment of the leg, which is called the tarsus. Most insects have claws, which may be large or small, depending on the type of insect.

CrossveinsThe crossveins are thin tubes present and visible in many insects’ wings. They run perpendicular (or nearly so) to the contain the insect’s crossveins veins, forming a network of small squares, rectangles and other windowpane-like shapes within the wing. Like the veins, the crossveins contain the insect’s blood, known as hemolymph.

Direct developmentDirect development, sometimes called ametamorphosis or ametabolous metamorphosis, is a type of metamorphosis seen in some insect groups. In direct development, insects go through three stages: eggs to immatures/nymphs to adults (the mature or imago stage). The nymph stage, however, is essentially indistinguishable from the adults. Other than the lack of functional reproductive organs, the nymphs look like the adults. The silverfish are examples of insects that exhibit direct development.

DorsalDorsal refers to the top side of an insect.

Dorsoventrally flattenedA dorsoventrally flattened insect is one that is flattened from top to bottom (like a penny that is laying flat on a table rather than standing on its end).

EntognathaEntognatha is a class of insect-like organisms that includes the orders Collembola, Diplura and Protura. The word entognatha refers to the mouthparts, which are contained inside a pouch that is within the head (ento is the Greek work for inside or within, and gnatha is the Greek word for jaw.

ExoskeletonIn humans and other vertebrates, the skeleton is inside the body. In insects, however, the skeleton is on the outside and it serves to protect and contain the organs and tissues inside it.

Parts of an Insect Leg
The insect leg has three main parts: the femur (thigh), the tibia (shin) and tarsus (foot). In addition, it has two smaller parts known as the trochanter and the coxa. The tiny lines at the end of the tarsus are the claws. some insects have larger claws and some have pads instead of claws.. Illustration credit: Nicholas W. Beeson.

FemurLike a human's leg, an insect’s leg is divided into three main parts. The three main parts of an insect leg are the femur (thigh), tibia (shin) and tarsus (foot). The femur is the main section closest to the body. In some insects, such as grasshoppers, the femur is much larger than the other leg sections.

ForelegsThe forelegs are the pair of legs that arise from the prothorax. They are the front pair of legs.

ForewingsThe forewings are the pair of wings that arise from the mesothorax. If an insect has two pairs of wings, the forewings are the front pair.

HalteresThe halteres are structures that take the place of one pair of wings in some insects. In flies, the halteres are knob-like structures that take the place of the hind wings. The halteres arise from the metathorax, which is the last segment of the thorax. They serve as balancing organs to assist the fly in flight. In twisted-wings, the halteres take the place of the forewings. No other insect groups have halteres.

HamuliThe hamuli are tiny hooks that link together the forewing and hind wing in insects within the order Hymenoptera, which includes the bees and wasps. Joining the wings together like this aids in the insect’s flight.

HeadAn insect’s body is divided into three main parts: the head, the thorax and the abdomen. The antennae, eyes and mouthparts are part of the head.

HemelytraThe hemelytra are a type of forewings seen in members of the suborderHeteroptera. A hemelytron (the single form of hemelytron) is thick at the base and membranous at the tip.

Hemimetabolous MetamorphosisHemimetabolous metamorphosis, also called incomplete or gradual metamorphosis, is a form of development seen in some insect groups. In hemimetabolous metamorphosis, insects go through three stages: eggs to immatures to adults (the mature or imago stage). The immature stage is called a nymph if it is terrestrial (lives on land) and a naiad if it lives in the water. Dragonflies, grasshoppers and earwigs are examples of insects that exhibit hemimetabolous metamorphosis. You may see the alternate term paurometabolous metamorphosis used for terrestrial insects that undergo hemimetabolous metamorphosis

Holometabolous MetamorphosisHolometabolous metamorphosis, also called complete metamorphosis, is a form of development seen in some insect groups. In holometabolous metamorphosis, insects go through four stages: egg to larva to pupa to adult (the mature or imago stage). Depending on the type of insect, the larva may be a caterpillar, grub, maggot, or some other form. As the larva enters the pupal stage, it reduces its movement and becomes encased in a cocoon or chrysalis. Examples of orders that exhibit holometabolous metamorphosis include Lepidoptera (butterflies and moths), Diptera (flies) and Coleoptera (beetles).

LarvaA larva is the immature form of an insect. It is typically used for the immature form of those insects that undergo holometabolous metamorphosis. Among those insects that undergo hemimetabolous metamorphosis, the immature form is typically called a nymph if it is terrestrial or naiad if is is aquatic.

Laterally flattenedA laterally flattened insect is one that is flattened from side to side (like a penny that is standing on end, rather than laying flat on a table).

MandiblesThe mandibles are an insect’s jaws. Insects that chew may have small or large, but typically noticeable mandibles, which move in a side-to-side fashion (rather than up and down, as human jaws do). Chewing insects include beetles, dragonflies and grasshoppers. Insects that pierce or suck rather than chew have modified mandibles. Piercing mouthparts may be shaped like blades that the insect uses to pierce a plant or an animal to reach its food. Mosquitoes and various true bugs have piercing mouthparts. Sucking mouthparts include tubes that the insect uses to draw up nectar or other fluids. Butterflies are examples of insects with sucking mouthparts. Some insects, including houseflies, have no mandibles. Instead, they have sponge-like mouthparts that the insects use to lap up liquids.

MembranousMembranous refers to a wing type. A membranous wing is one that is thin and filmy. Depending on the insect, membranous wings may be clear (as in most dragonflies) or opaque and sometimes quite colorful (as in most butterflies and moths).

MesothoraxThe mesothorax is the middle segment of the thorax. The thorax has three segments. From front to back, they are: the prothorax, the mesothorax and the metathorax. If the insect has two pairs of wings, one pair arises from the mesothorax and one from the metathorax. If the insect has one pair of wings, that pair may arise from either the mesothorax (as in flies) or the metathorax (as in twisted-wings.

MetathoraxThe metathorax is the hind segment of the thorax. The thorax has three segments. From front to back, they are: the prothorax, the mesothorax and the metathorax. If the insect has two pairs of wings, one pair arises from the mesothorax and one from the metathorax. If the insect has one pair of wings, that pair may arise from either the mesothorax (as in flies) or the metathorax (as in the twisted-wings).

NaiadA naiad is the immature form of those types of aquatic insects that undergo hemimetabolous metamorphosis. Examples of insects that have a naiad form are dragonflies and mayflies.

Net-veinedNet-veined refers to the network of veins and crossveins that form windowpane-like patterns within the wing in some insects. Some insects, such as lacewings have extensive “windowpanes” in their wings, giving them a lacy quality.

NymphA nymph is the immature form of those types of insects that undergo hemimetabolous metamorphosis. Nymphs of terrestrial insects typically look like wingless versions of the adult form. Examples of insects that have a nymph form are true bugs and grasshoppers. Nymphs of aquatic insects are more correctly called naiads.

OcelliInsects may have two types of eyes: compound eyes and simple eyes, which are called ocelli. Many insects have two noticeable compound eyes and a number of small ocelli that often look like little more that slight spots on the “forehead.” Some insects lack compound eyes and/or ocelli.

OvipositorThe ovipositor is an egg-laying structure that is obvious in some female insects as a long appendage that extends from the rear of the abdomen. In some female insects, such as female katydids (in the order Orthoptera), the ovipositor looks like a spear. In others, such as the female snakeflies (in the order Raphidioptera), the ovipositor may look more like a stinger.

PronotumThe pronotum is the upper surface of the prothorax. In some insects the pronotum is extended forward over the head (as in cockroaches) or backward over the abdomen (pygmy grasshoppers).

ProthoraxThe prothorax is the first segment of the thorax. The thorax has three segments. From front to back, they are: the prothorax, the mesothorax and the metathorax. One pair of legs arises from each of the three thoracic segments. If the insect has two pairs of wings, one pair arises from the mesothorax, and one pair arises from the metathorax.

PupaA pupa is a development stage in of those insects that undergo holometabolous metamorphosis. Such insects’ develop from eggs to larvae to pupae to adults. Depending on the type of insect, the pupal stage may last from a matter of days to several years.

RostrumThe rostrum is the piercing mouthparts present in true bugs. The rostrum is often described as similar to a blade or long beak. Many true bugs hold their rostrum down and along their ventral side when it is not in use. When a true bug is feeding, it swings out the rostrum to pierce plant or animal tissue (depending on that particular species’s diet) and suck up the fluid within. The long snout of weevils (a group of beetles) is also sometimes called a rostrum, but it is not like a true bug’s rostrum. A weevil has jaws at the end of the rostrum, which is stationary, and it does not use its snout for piercing.

StyliThe styli are small, rudimentary, leg-like structures that extend from the abdomen of some adult insects, such as silverfish. An insect’s legs, in contrast, extend from the thorax. Insects have only six true legs.

Sucking mouthpartsSuctorial, mouthparts come in a number of different varieties. For instance, butterflies have long tubes that they use like straws to suck up nectar from plants. When it isn’t feeding, the butterfly coils up the tube. Many true bugs, such as stink bugs, have spear-like mouthparts that pierce into a plant so that the insect can suck up the plant juices. Some flies, including mosquitoes, have needle-like mouthparts that can slide into an animal’s skin, and allow access to the blood.

TarsusLike a human's leg, an insect’s leg is divided into three main parts. The three main parts of an insect leg are the femur (thigh), tibia (shin) and tarsus (foot). Many insect orders have a characteristic number of segments within the tarsus.

Tegmina Tegmina are the leathery forewings present in some insects, such as earwigs, which have short tegmina; and grasshoppers, which typcially have longer tegmina. Tegmina is plural; the singular is tegmen.

ThoraxThe thorax is the second of an insect’s three main body parts. The three body parts from front to back are: the head, the thorax and the abdomen. Both the legs and the wings arise from the thorax.

TibiaLike a human's leg, an insect’s leg is divided into three main parts. The three main parts of an insect leg are the femur (thigh), tibia (shin) and tarsus (foot). The tibia is the middle of the three main sections.

VeinsVeins are thin, longitudinal, tubes present and visible in most insects’ wings. The veins contain the insect’s blood, which is called hemolymph, are are therefore part of the insect’s circulatory system. In many insects, other smaller crossveins run perpendicular (or nearly so) to the veins, forming a network of small squares, rectangles and other windowpane-like shapes within the wing.

VentralVentral refers to the underside of an insect.



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Photos at the top of this website are (from left to right): potato beetle (Leptinotarsa decemlineata) — photo credit: Scott Bauer, U.S. Department of Agriculture; ebony jewelwing (Calopteryx maculata)— photo credit: U.S. Fish and Wildlife Service; sweat bee (Agapostemon splendens) — photo credit: Natalie Allen and Stephanie Kolski, U.S. Geological Survey; preying mantis, monarch butterfly (Danaus plexippus), hellgrammite (aka toe biter) larva and eyed click beetle (Alaus oculatus) — photo credit: Leslie Mertz, DailyGraceCards.com; Halloween pennant (Celithemis eponina) — photo credit: Kay Meng, U.S. Fish and Wildlife Service.

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