''Notonecta glauca'', also known as the greater water-boatman or common backswimmer, is a species of aquatic insect in the family

Notonectidae Notonectidae is a Cosmopolitan distribution, cosmopolitan family of aquatic insects in the order Hemiptera, commonly called backswimmers because they swim "upside down" (inverted). They are all predators and typically range from in length. They ...

. 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 water-boatmen. ''Notonecta glauca'' are ''

Hemiptera Hemiptera (; ) is an order of insects, commonly called true bugs, comprising more than 80,000 species within groups such as the cicadas, aphids, planthoppers, leafhoppers, assassin bugs, bed bugs, and shield bugs. They range in size from ...

'' (true bug) 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 (hence their common name "backswimmer" or "water boatman") 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 (

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

). 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.

Eye

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 An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

. 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 A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation ...

properties * having a robust migration of pigment and photoreceptors They also found that the green-sensitive peripheral photoreceptors function in a similar way as nocturnal

Phasmatodea The Phasmatodea (also known as Phasmida or Phasmatoptera) are an Order (biology), order of insects whose members are variously known as stick insects, stick bugs, walkingsticks, stick animals, or bug sticks. They are also occasionally referred ...

(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 The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

. 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 The pupil is a hole located in the center of the iris of the eye that allows light to strike the retina.Cassin, B. and Solomon, S. (1990) ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishing Company. It appears black becau ...

(acone) take a different amount of time to adjust to

light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...

. 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.

Air retention

Although ''N. glauca'' live in the water, they breathe

atmospheric An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere ...

air and do not have

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

s. When these insects are diving or resting under the water surface, they create a film of air that surrounds their body. This air film is also known as a superhydrophobic coating or surface, and it prevents the insect from becoming wet. It also reduces the

drag (physics) In fluid dynamics, drag, sometimes referred to as fluid resistance, is a force acting opposite to the direction of motion of any object moving with respect to a surrounding fluid. This can exist between two fluid layers, two solid surfaces, or b ...

that is created when diving. To be able to create this air film around it, ''N. glauca'' is covered in hairy structures, except on its head and legs. There are two types of hairs and air retention is maximized by having both types:

setae In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae ...

and microtrichia. The most important part in creating an air film is the density of the hairs. ''Notonecta glauca'' has dense microtrichia and their air film can last up to 120 days. The air film cannot last forever because as an insect respires ( breathes), the

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

will decrease and

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

will increase, causing the air bubble to decrease in size.

Model organism

''Notonecta glauca'' is used as a model organism for friction reduction and air retention. Possible applications for this include reduction of drag in ships.

Wave discrimination

''Notonecta glauca'' can discriminate between

prey Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...

and non-prey, like other backswimmers, by

surface wave In physics, a surface wave is a mechanical wave that propagates along the Interface (chemistry), interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occu ...

s. Lang (1979), completed an experiment that showed that

wave In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...

s that were created by other backswimmers

swimming Swimming is the self-propulsion of a person through water, such as saltwater or freshwater environments, usually for recreation, sport, exercise, or survival. Swimmers achieve locomotion by coordinating limb and body movements to achieve hydrody ...

, emerging, turning and

paddling Paddling, in regard to waterborne transport, is the act of propelling a human-powered watercraft using at least one hand-held paddle. The paddle, which consists of one or two blades joined to a shaft, is also used to steer the vessel via generatin ...

were of a lower

frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...

(below 40 Hz) compared to

s created by their

items, who had a

between 70–140 Hz.

Larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l backswimmers were found to create different

s that differed from adult backswimmers, but their

were similar to that of adult swimming produced waves (up to 70 Hz).

Foraging behaviour

Water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

depth can affect how ''N. glauca'' pick which prey they eat. Males and females both spend a lot of time on the surface of the water where they encounter mosquito (''

Culex ''Culex'' or typical mosquitoes are a genus of mosquitoes, several species of which serve as vectors of one or more important diseases of birds, humans, and other animals. The diseases they vector include arbovirus infections such as West Nil ...

'')

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e. They feed on this prey because there is a decrease in travel cost (having to dive for them) and ''Culex'' gives a higher energy rate. Mature females, however, will also dive to the bottom of the pond to feed on isopods (''

Asellus ''Asellus'' is a genus of isopod crustaceans in the family Asellidae. Species ''Asellus'' is divided into three subgenera which contain the following species: ''Asellus (Asellus)'' Geoffroy, 1762 * ''Asellus amamiensis'' Matsumoto, 1961 * ''As ...

''), but only in shallow waters. Reaching ''Asellus'' requires a higher travel cost of

energy Energy () is the physical quantity, quantitative physical property, property that is transferred to a physical body, body or to a physical system, recognizable in the performance of Work (thermodynamics), work and in the form of heat and l ...

. This behaviour is not consistent with the

optimal foraging theory Optimal foraging theory (OFT) is a behavioral ecology model that helps predict how an animal behaves when searching for food. Although obtaining food provides the animal with energy, searching for and capturing the food require both energy and ti ...

. It is possible, however, that because mature females are larger than males and immature females, they have a reduced

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

and therefore require less energy to capture ''Asellus''. Also, mature females have a larger abdominal size, which could support a larger air bubble and allow them to remain submerged for longer. However, if the water depth increases, mature females will switch and spend more time at the surface and not feed on ''Asellus'', as the deep water increases the amount of energy needed for diving and staying submerged. The oxygen concentration in the body of water can affect the choice of prey ''N. glauca'' pick, as Cockrell (1984) found that when oxygen was at a high dissolved level, ''N. glauca'' will spend more time submerged and attacking ''Asellus''. Notonecta

References

External links

arkive.org

naturespot.org.uk

Bug Guide

YouTube Videos

* https://www.youtube.com/watch?v=_TlBmQNfSc4 * https://www.youtube.com/watch?v=aHI-5bb_I2g * https://www.youtube.com/watch?v=1Uq3NUpM_zE * https://www.youtube.com/watch?v=E9i34x5A9v0 {{Taxonbar, from=Q266370 Hemiptera of Europe Insects described in 1758 Notonecta Taxa named by Carl Linnaeus