| Tactile | able to be touched, pertaining to touch |
| Tagma, tagmata | a body segment of an arthropod resulting from the embryotic fusion of two or more segments, as in insects which have a head , thorax and abdomen |
| Tagmosis | organisation of the arthropod body into tagamata (segments) |
| Taiga | The coniferous or boreal forest biome, characterised by snow, harsh winters, short summers, and evergreen trees. |
| Tarsus/tarsi | the jointed feet of some animals such as insects |
| Taxis | A movement towards or away from some stimulus. |
| Taxon | a taxonomic group or entity |
| Taxonomy | The branch of biology concerned with naming and classifying the diverse forms of life. |
| Tegmen | plural = tegmina The leathery forewing of some insects, e.g. crickets and cockroaches. |
| Tegula | a covering over the structures which articulate the wings with the thorax at the base of the wing, see the diagram of the bumblebee body |
| Telson | Posterior projection of the last body segment in some crustaceans and horseshoe crabs |
| Tentacle | a slender, flexible, projecting structure; can be sensory or used for food capture. |
| Tergum/tergite | dorsal part of an arthropod body segment |
| Terminal | the last or end of a series |
| Terrestrial | Living wholly or mainly on the ground |
| Territory | An area defended by an animal, or group of animals, against other animals. |
| Test | In echinoderms, the skeleton made of calcareous plates. |
| Thermoregulation | The maintenance of internal temperatures within a tolerable range, see Bumblebees. |
| Thigmotaxis | the tendency to press the body against a surface or into a corner, as seen in Dermaptera - earwigs. |
| Thorax | The middle region of an arthropod's body. It contains the powerful muscles that operate the legs and wings, see bumblebee |
| Tibia | In insects, the part of the leg immediately above the tarsus or foot. |
| Tissue | An integrated group of cells with a common structure and function. |
| Tracheae | Tiny air tubes that ramify through the insect body for gas exchange. |
| Trilobites | A group of animals that became extinct at the end of the Permian. They were marine and resembled woodlice externally. |
| Torpor | A sleep-like state in which the body processes slow down. Animals usually become torpid to survive difficult conditions, e.g. cold or lack of food. |
| Torsion | a process of twisting during growth, e.g. in snails |
| Tracheal system | A system of minute tubes found in insects and arachnids used to carry oxygen into their bodies. The air enters through the spiracles (small openings found down the sides of the thorax and abdomen) and flows through the branching trachea to the cells. |
| Tracheoles | the very fine ends of tracheal tubes |
| Transverse | wider than long |
| Trivoltine | having three generation a year |
| Trochanter | the second segment from the body of an insect's leg, between the coxa and the femur |
| Trophallaxis | The exchange of alimentary liquid among social insect colony members and their guests. In stomodeal trophallaxis the material originates from the mouth; in proctodeal trophallaxis the material originates from the anus. |
| Trophic structure | The different feeding levels of an ecosystem which determines the route of energy flow and the pattern of chemical cycling. |
| Tropical rain forest | The most complex of all communities located near the equator where rainfall is abundant. It has many more species of plants and animals than any other ecosystem. |
| Truncate | cut off or blunt |
| Tube foot | a hydraulic organ protruding from the bodies of most echinoderms |
| Tubercle | A hard swelling on an animal's body. |
| Tundra | A biome at the northernmost limit of plant growth and at high altitudes, where plant forms are limited to low, shrubby or mat-like vegetation. |
| Tunic | in tunicates a cuticular, cellulose-containing covering of the body |
| Tymbal organ | Drum-like organs on either side of a cicada's abdomen that vibrate to produce sound. |
| Tympanum | an auditory organ consisting of a vibration-sensitive membrane on the abdomen or forelegs of grasshoppers and some moths |
| Univoltine | having a single generation a year |
| Uric acid | The insoluble precipitate of nitrogenous waste excreted by land snails, insects, birds and some reptiles. |
| Uropod | Posterior appendage of many crustaceans |
| Valve | one of the two shells of a bivalve mollusc or a brachiopod |
| Variation | Differences among individuals in a species that have nothing to do with age, sex, or position. |
| Vascular | containing blood vessels |
| Vector | An agent that carries and transmits a pathenogenic microorganism from one animal to another, e.g. fleas transmit the plague bacterium, Pasturalla pestis to rats and man. |
| Veins | Vessels that return blood to the heart. |
| Ventral | On or near the underside |
| Vermiform | worm-like |
| Venation | the patterns of veins in an insect's wing |
| Vestigial | Relating to an organ that has atrophied or is non-functioning, e.g. vestigial wings of some insects. |
| Viviparous | producing live young rather than eggs |
| Voltinism | the number of generations per year |
| Waggle dance | The dance whereby workers of various species of honey bee communicate the location of food and new nest sites. The basic dance is a figure of 8 pattern with the middle part of the 8 containing the information about the direction and distance of the target. |
| Warning colouration | A combination of contrasting colours that warns that an animal is dangerous, e.g. black/yellow of insects. |
| Water vascular system | In echinoderms, a system of fluid-filled tubes and chambers that connects with the tube-feet. The fluid in the water vascular system is under pressure, giving the tube-feet their shape. |
| Wing case | the hardened first pair of wings of some beetles and bugs |
| Worker | The infertile member of a colony of social insects, e.g. bumblebees |