a small creature such as a fly or ant, that has six legs, and sometimes wings.——朗文当代大辞典

A small invertebrate animal, usually having a body divided into segments, and several pairs of legs, and often winged; in popular use comprising, besides the animals scientifically so called (see 2), many other arthropods, as spiders, mites, centipedes, wood-lice, etc., and other invertebrates, as the ‘coral-insect’; formerly (and still by the uneducated) applied still more widely, e.g. to earthworms, snails, and even some small vertebrates, as frogs and tortoises.——牛津当代大辞典  @en