section_path: Morphology and physiology/Internal systems/Sensory
section_name: Sensory
paragraph_text: Sensory
  
  Many insects possess numerous specialized sensory organs able to detect stimuli including limb position (proprioception) by campaniform sensilla, light, water, chemicals (senses of taste and smell), sound, and heat. Some insects such as bees can perceive ultraviolet wavelengths, or detect polarized light, while the antennae of male moths can detect the pheromones of female moths over distances of over a kilometer. There is a trade-off between visual acuity and chemical or tactile acuity, such that most insects with well-developed eyes have reduced or simple antennae, and vice versa. Insects perceive sound by different mechanisms, such as thin vibrating membranes (tympana). Insects were the earliest organisms to produce and sense sounds. Hearing has evolved independently at least 19 times in different insect groups.
  
  Most insects, except some cave crickets, are able to perceive light and dark. Many have acute vision capable of detecting small and rapid movements. The eyes may include simple eyes or ocelli as well as larger compound eyes. Many species can detect light in the infrared, ultraviolet and visible light wavelengths, with color vision. Phylogenetic analysis suggests that UV-green-blue trichromacy existed from at least the Devonian period, some 400 million years ago.
  
  The individual lenses in compound eyes are immobile, but fruit flies have photoreceptor cells underneath each lens which move rapidly in and out of focus, in a series of movements called photoreceptor microsaccades. This gives them, and possibly many other insects, a much clearer image of the world than previously assumed.
  
  An insect's sense of smell is via chemical receptors, usually on the antennae and the mouthparts. These detect both airborne volatile compounds and odorants on surfaces, including pheromones from other insects and compounds released by food plants. Insects use olfaction to locate mating partners, food, and places to lay eggs, and to avoid predators. It is thus an extremely important sense, enabling insects to discriminate between thousands of volatile compounds.
  
  Some insects are capable of magnetoreception; ants and bees navigate using it both locally (near their nests) and when migrating. The Brazilian stingless bee detects magnetic fields using the hair-like sensilla on its antennae.