Pleidae
Encyclopedia
Pleidae, the pygmy backswimmers, is a family
of aquatic insect
s in the order
Hemiptera
(infraorder Nepomorpha
, or "true water bugs"). There are 37 species
in three genera
, distributed across most of the world, except the polar region
s and remote ocean
ic islands.
Pleidae belong to the Tripartita which contains the more advanced lineages of true water bugs, and are closely related to the true backswimmers (Notonectidae), but closer still to the Helotrephidae, another family of tiny Nepomorpha
, which usually swim upside-down and, like the Pleidae, have a sensory organ in the center of the clypeus
. Either the pygmy backswimmers are united with the Helotrephidae in the superfamily
Pleoidea, or these two and the true backswimmers are placed in a single superfamily Notonectoidea.
there is a single species, Plea minutissima, widely found in that continent. Plea species occur in the Old World
, while Neoplea is found in the Americas
. Paraplea can be found in all warmer parts of Earth, including Australia
, where three species occur. Given their inability to fly well – if they can fly at all –, it is not surprising that the Pleidae do not have as many endemic island taxa as some other Heteroptera
(true bugs). Only five species are known from the entire Malesia
n archipelago
for example. Neoplea apopkana has been introduced to the Hawaiian Islands
in Polynesia
. One species, originally native to South Asia
and Southeast Asia
, was found in aquaria
in New Zealand
. In 2006, Paraplea puella was found to be introduced to Guam
in Micronesia
. Like in the preceding case, this originally American
species was probably accidentally introduced with aquarium plants.
are only 2–3 mm long and usually of a light brownish color overall. Their body is oval, plump, with a concave back. Their compound eyes are large and the ocelli vestigial, like in other Nepomorpha
. Also characteristic for the infraorder are the short and weak antenna
e which are usually carried tucked to the head. In the case of the Pleidae the antennae are shorter than the head is long and only consist of three segments.
The scutellum is small and triangular. The wings are reduced in some fully flightless species, but normally developed in most; due to their compact, rotund bodies and generally short wings, even those with well-developed wings fly weakly at best. By and large the Pleidae may be considered an effectively flightless group when it comes to biogeography
and dispersal into new habitat
.
The tarsi
consist of two or three segmnents; two claws are borne on the last tarsal segment of the hindlegs. Though the hindlegs are hairless and appear ill-suited for swimming compared to the stout "flippers" of the water boatmen (Corixidae) or the backswimmers (Notonectidae), the small size of the pygmy backswimmers makes for different physics
and allows them to swim well regardless.
Both sexes are able to stridulate. The sounds they produce apparently have an intraspecific
communication
function, as the animals are able to perceive and react to them. Possibly they make sounds to maintain contact among the loose swarm
s in which the Pleidae roam their habitat
.
The larva
e have gland
s between the third and fourth abdominal tergite. Development is direct, without a pupa
l stage.
ecosystem
s, where they occur in loose groups. Like many of their relatives, they are predatory, hunting other tiny invertebrate
s, from which they suck out the body fluids with their rostrum
. They can to some extent biologically control mosquito
larvae. Unlike true backswimmers (Notonectidae), they are completely harmless to humans, as their rostrum is far too small to pierce skin.
Their hindleg claws enable them to clamber through vegetation which apart from swimming is their main form of locomotion
. Like Notonectidae, they are in an upside-down position when swimming. This is ultimately because as all true water bugs, Pleidae are air-breathers without gill
s. Similar to the true backswimmers, pygmy backswimmers carry an air reserve with them which is periodically replenished by a dash to the water's surface. This air is contained in a felt-like cushion on the underside. Thus, the belly has higher buoyancy
, resulting in the animal turning upside down as soon as it lets loose from the substrate
.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of aquatic insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s in the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...
(infraorder Nepomorpha
Nepomorpha
Nepomorpha is an infraorder of insects in the "true bug" order . They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world outside the polar regions, with about 2,000 species altogether...
, or "true water bugs"). There are 37 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
in three genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
, distributed across most of the world, except the polar region
Polar region
Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. The North Pole and South Pole being the centers, these regions are dominated by the polar ice caps, resting respectively on the Arctic Ocean and the continent of Antarctica...
s and remote ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
ic islands.
Pleidae belong to the Tripartita which contains the more advanced lineages of true water bugs, and are closely related to the true backswimmers (Notonectidae), but closer still to the Helotrephidae, another family of tiny Nepomorpha
Nepomorpha
Nepomorpha is an infraorder of insects in the "true bug" order . They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world outside the polar regions, with about 2,000 species altogether...
, which usually swim upside-down and, like the Pleidae, have a sensory organ in the center of the clypeus
Clypeus
The clypeus is one of the sclerites that makes up the "face" of an arthropod.In insects, the clypeus delimits the lower margin of the face, with the labrum articulated along the ventral margin of the clypeus. The mandibles bracket the labrum, but do not touch the clypeus. The dorsal margin of the...
. Either the pygmy backswimmers are united with the Helotrephidae in the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
Pleoidea, or these two and the true backswimmers are placed in a single superfamily Notonectoidea.
Distribution
In EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
there is a single species, Plea minutissima, widely found in that continent. Plea species occur in the Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
, while Neoplea is found in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
. Paraplea can be found in all warmer parts of Earth, including Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, where three species occur. Given their inability to fly well – if they can fly at all –, it is not surprising that the Pleidae do not have as many endemic island taxa as some other Heteroptera
Heteroptera
Heteroptera is a group of about 40,000 species of insects in the Hemiptera. Sometimes called "true bugs", that name more commonly refers to Hemiptera as a whole, and "typical bugs" might be used as a more unequivocal alternative since among the Hemiptera the heteropterans are most consistently and...
(true bugs). Only five species are known from the entire Malesia
Malesia
Malesia is a biogeographical region straddling the boundaries of the Indomalaya ecozone and Australasia ecozone, and also a phytogeographical floristic region in the Paleotropical Kingdom.-Floristic province:...
n archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
for example. Neoplea apopkana has been introduced to the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
in Polynesia
Polynesia
Polynesia is a subregion of Oceania, made up of over 1,000 islands scattered over the central and southern Pacific Ocean. The indigenous people who inhabit the islands of Polynesia are termed Polynesians and they share many similar traits including language, culture and beliefs...
. One species, originally native to South Asia
South Asia
South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
and Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
, was found in aquaria
Aquarium
An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
. In 2006, Paraplea puella was found to be introduced to Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
in Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
. Like in the preceding case, this originally American
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
species was probably accidentally introduced with aquarium plants.
Description
These tiny HemipteraHemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...
are only 2–3 mm long and usually of a light brownish color overall. Their body is oval, plump, with a concave back. Their compound eyes are large and the ocelli vestigial, like in other Nepomorpha
Nepomorpha
Nepomorpha is an infraorder of insects in the "true bug" order . They belong to the "typical" bugs of the suborder Heteroptera. Due to their aquatic habits, these animals are known as true water bugs. They occur all over the world outside the polar regions, with about 2,000 species altogether...
. Also characteristic for the infraorder are the short and weak antenna
Antenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
e which are usually carried tucked to the head. In the case of the Pleidae the antennae are shorter than the head is long and only consist of three segments.
The scutellum is small and triangular. The wings are reduced in some fully flightless species, but normally developed in most; due to their compact, rotund bodies and generally short wings, even those with well-developed wings fly weakly at best. By and large the Pleidae may be considered an effectively flightless group when it comes to biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
and dispersal into new habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
.
The tarsi
Arthropod leg
The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments are of Latin origin, and may be confused with terms for bones: coxa , trochanter , femur, tibia, tarsus, ischium, metatarsus, carpus, dactylus ,...
consist of two or three segmnents; two claws are borne on the last tarsal segment of the hindlegs. Though the hindlegs are hairless and appear ill-suited for swimming compared to the stout "flippers" of the water boatmen (Corixidae) or the backswimmers (Notonectidae), the small size of the pygmy backswimmers makes for different physics
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
and allows them to swim well regardless.
Both sexes are able to stridulate. The sounds they produce apparently have an intraspecific
Intraspecific
Intraspecific is a term used in biology to describe behaviors, biochemical variations and other issues within individuals of a single species, thereby contrasting with interspecific. For example:* Intraspecific antagonism...
communication
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
function, as the animals are able to perceive and react to them. Possibly they make sounds to maintain contact among the loose swarm
Swarm
Swarm behaviour, or swarming, is a collective behaviour exhibited by animals of similar size which aggregate together, perhaps milling about the same spot or perhaps moving en masse or migrating in some direction. As a term, swarming is applied particularly to insects, but can also be applied to...
s in which the Pleidae roam their habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
.
The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e have gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
s between the third and fourth abdominal tergite. Development is direct, without a pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
l stage.
Ecology
Pygmy backswimmers inhabit lacustrineLake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s, where they occur in loose groups. Like many of their relatives, they are predatory, hunting other tiny invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, from which they suck out the body fluids with their rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
. They can to some extent biologically control mosquito
Mosquito
Mosquitoes are members of a family of nematocerid flies: the Culicidae . The word Mosquito is from the Spanish and Portuguese for little fly...
larvae. Unlike true backswimmers (Notonectidae), they are completely harmless to humans, as their rostrum is far too small to pierce skin.
Their hindleg claws enable them to clamber through vegetation which apart from swimming is their main form of locomotion
Animal locomotion
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
. Like Notonectidae, they are in an upside-down position when swimming. This is ultimately because as all true water bugs, Pleidae are air-breathers without gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s. Similar to the true backswimmers, pygmy backswimmers carry an air reserve with them which is periodically replenished by a dash to the water's surface. This air is contained in a felt-like cushion on the underside. Thus, the belly has higher buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
, resulting in the animal turning upside down as soon as it lets loose from the substrate
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...
.