page_title: Notonecta glauca
section_title: Eye
hierarchical_section_title: Notonecta glauca / Eye
caption_attribution_description: Eyes of the beholder
context_page_description: Notonecta glauca is a species of aquatic insect, and a type of backswimmer. This species is found in large parts of Europe, North Africa, and east through Asia to Siberia and China. In much of its range it is the most common backswimmer species. It is also the most widespread and abundant of the four British backswimmers. Notonecta glauca are Hemiptera predators, that are approximately 13–16 mm in length. Females have a larger body size compared to males. These water insects swim and rest on their back and are found under the water surface. Notonecta glauca supports itself under the water surface by using their front legs and mid legs and the back end of its abdomen and rest them on the water surface; They are able to stay under the water surface by water tension, also known as the air-water interface. They use the hind legs as oars; these legs are fringed with hair and, when at rest, are extended laterally like a pair of sculls in a boat. Notonecta glauca will either wait for its prey to pass by or will swim and actively hunt its prey. When the weather is warm, usually in the late summer and autumn, they will fly between ponds. Notonecta glauca reproduce in the spring.
context_section_description: There has been a great deal of research on the eye of N. glauca. These insects use their eyes for both day and night vision, which is used for prey capture and flight when searching for new habitats. Notonecta glauca, like other insects, have a compound eye. 
  Specifically, their eye is an acone-type with corneal structure, which helps them create a sharp image when both in the water and in the air. The acone is the site of the pupil. Immonen et al. (2014), found that backswimmers are able to see in both day and night light conditions because of:
  their large variations in the peripheral photoreceptor cell properties
  having a roust migration of pigment and photoreceptors
  They also found that the green-sensitive peripheral photoreceptors function in a similar way as nocturnal Phasmatodea (or stick insects). 
  To protect their eye from direct sunlight during the day, the pigment cell's diaphragm are condensed, and during the night they open fully to allow as much light in as possible. Notonecta glauca have two photoreceptor subsystems: 
  Large and most sensitive peripheral photoreceptors
  Smaller peripheral and central photoreceptors
  The first subsystem is sensitive to green light, one of the colours in the visible spectrum. This sensitivity helps the backswimmer see in dimmer light or at night. The second subsystem allows the backswimmer to see in bright light and when in flight. Notonecta glauca pupil (acone) take a different amount of time to adjust to light. It takes the N. glauca approximately 40 minutes for the pupil to adjust to daylight and approximately 50 minutes to adjust to the light at night.
caption: Compound eye
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