| Nacre | The innermost, lustrous layer of a mollusc shell, secreted by the mantle, mother-of-pearl. |
| Natality | births |
| Natural history | the study of nature |
| Native | Indigenous. Living naturally within a given area. |
| Naturalized | an alien, or introduced species, that has become successfully established |
| Natural selection | The differential success in reproduction of different phenotypes resulting from the interaction of organisms with their environment |
| Nauplius | the earliest larval stage of Crustaceans when they (usually) have 3 pairs of functioning limbs |
| Nautiloid | A free-swimming marine animal in the phylum Mollusca. It has a coiled, chambered cell. |
| Nectar | the sugary substance secreted by flowers to attract insects so aiding pollination |
| Nectarivorous | feeding on nectar |
| Nematocyst | the stinging cell of cnidarians |
| Nematodes | Unsegmented round worms, usually small, often parasitical. |
| Nematomorpha | hairworms, Gordian worms, horsehair worms |
| Nemertea | ribbon worms |
| Neonatal | newborn, recently hatched |
| Neoteny | the retention of juvenile features into the adult stage |
| Nephridium | a excretory tube in earthworms |
| Nest odour | the distinctive odour of a nest enabling the inhabitants to distinguish their nest from the others, e. g. as in social hymenoptera |
| Nest parasitism | symbiosis between 2 termite species where one colony lives in and feeds on the walls of the nest of another (host) species |
| Neurons | Nerve cells which receive and transmit stimuli. |
| Neuroptera | the order of insects containing the lacewings, alder flies, ant lions etc. |
| Neurotoxin | A substance that deactivates nerves or that disrupts the way nerves work. Some insects can produce neurotoxins and they are commonly found in many insecticides. |
| Niche | the limits for all important environmental features, within which individuals of a species can survive, grow and reproduce. |
| Nit | an egg of a louse, especially the human head louse |
| Noctuidae | family of moths containing the cutworms and army worms |
| Nocturnal | Active at night |
| Nomad | a wandering organism |
| Nomenclature | the system and application of scientific naming of species |
| Noosphere | that part of the biosphere altered or influenced by man |
| Notochord | A reinforcing rod that runs the length of the body. It is found in chordates. |
| Notostraca | tadpole shrimp |
| Nucleus | The central body in a eukaryotic cell. It contains the genetic information on chromosomes. |
| Nuda | a class of sea gooseberry (Ctenophora) |
| Nuptial flight | the mating flight of insects, especially social insects, where it involves the queen mating with males. |
| Nutrient cycle | the path of a chemical substance (carbon, nitrogen, etc.) back and forth between the living and non-living worlds |
| Nymph | the immature stage of certain insects in which there is some similarity to the adult form |