Physogastrism or physogastry is a characteristic of certain arthropods (mostly insects and mites), where the abdomen is greatly enlarged and membranous. The most common examples are the "queens" of certain species of eusocial insects such as

termite Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattode ...

bee Bees are winged insects closely related to wasps and ants, known for their roles in pollination and, in the case of the best-known bee species, the western honey bee, for producing honey. Bees are a monophyletic lineage within the superfami ...

s and

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22,0 ...

s, in which the abdomen swells in order to hold enlarged

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

, thus increasing fecundity. This means that the queen has the ability to hold more and produce more eggs at one time. Physogastric queens produce an enormous number of eggs which can account for a significant amount of their body weight. In the termite species '' Macrotermes subhyalinus'', eggs can make up a third of their body weight, and a 15-gram queen can produce up to 30 eggs per minute. The physogastric queens' egg production is supported by oocyte proteins supplied by the "queen body fat."

In termites

Physogastrism in

s presents itself in quite an unusual manner. Unlike most physogastric insects, the queen termite is able to increase its size without the use of cuticular molting. Rather, the queen unfolds and stretches her abdominal

epicuticle The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda. Morphology In arthropods, the integument, the external "skin", or "s ...

in order to make room for the subsequent egg deposits. This process has been observed to be incredibly slow (sometimes over the course of several years).

In bees

Many

stingless bee Stingless bees, sometimes called stingless honey bees or simply meliponines, are a large group of bees (about 550 described species), comprising the tribe Meliponini (or subtribe Meliponina according to other authors). They belong in the family ...

species have physogastric queens, such as the South American species ''

Paratrigona subnuda ''Paratrigona subnuda'', commonly known as the jataí-da-terra ("ground jataí"), is a species of eusocial stingless bee in the family Apidae and tribe Meliponini. These social bees are prevalent in Neotropical moist forests, including Brazilia ...

'' and ''

Schwarziana quadripunctata ''Schwarziana quadripunctata'' is a small, stingless bee found in a stretch of the South American Amazon from Goiás, Brazil, through Paraguay, to Misiones, Argentina.Michener, C.D. (2007). ''The Bees of the World''. Baltimore: Johns Hopkins Uni ...

''. Physogastrism can also be seen in the stingless bee species '' Melipona bicolor'', which is facultatively polygynous, and therefore one or more physogastric queens can be found in the same colony.Koedam, D., et al. "The behaviour of laying workers and the morphology and viability of their eggs In ''Melipona bicolor bicolor''." Physiological Entomology 26.3 (2001): 254-259. Academic Search Premier. Web. 26 Sept. 2015. These queens interact with each other within the colony, and during the patrolling phase, a queen may attempt to touch the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

of another queen. The other queen turns her abdomen away, and what follows is the two queens circling one another, trying to touch the other's abdomen; as such, the queens are almost always active.Hayo H.W. Velthuis, Han De Vries, Vera L. Imperatriz-Fonseca. The polygyny of ''Melipona bicolor'': scramble competition among queens. Apidologie, Springer Verlag (Germany), 2006, 37 (2), pp.222-239.

In non-social insects and other arthropods

Various lineages of non-social insects demonstrate various degrees of physogastry, especially among females. The most dramatic and best-known are among the

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s, especially certain groups that live inside ant or termite nests, where the distended abdomen is thought to enhance integration into their hosts' colonies, though it is also seen in several herbivorous beetle lineages such as

Chrysomelidae The insects of the beetle family Chrysomelidae are commonly known as leaf beetles, and include over 37,000 (and probably at least 50,000) species in more than 2,500 genera, making up one of the largest and most commonly encountered of all beetle ...

(e.g., ''

Gastrophysa ''Gastrophysa'' is a genus of beetles in the family Chrysomelidae, in which the females typically exhibit swollen, membranous abdomens, a condition known as physogastrism. Species These nine species belong to the genus ''Gastrophysa'': * '' G ...

'') and

Meloidae Blister beetles are beetles of the family Meloidae, so called for their defensive secretion of a blistering agent, cantharidin. About 7,500 species are known worldwide. Many are conspicuous and some are aposematically colored, announcing their ...

(e.g., ''

Megetra ''Megetra'' is a genus of blister beetle Blister beetles are beetles of the family Meloidae, so called for their defensive secretion of a blistering agent, cantharidin. About 7,500 species are known worldwide. Many are conspicuous and some a ...

''). Females of endoparasitic fleas, in particular in the genus '' Tunga'', exhibit severe physogastry once they have penetrated the host's skin and begun to produce eggs. Many

Acari Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

(ticks and mites) have physogastric females, sometimes involving precocious development of offspring inside the mother's body.C.R. Ferreira de Oliveira, L.R. D’Antonino Faroni, R.N. Carvalho Guedes, A. Pallini, J.R. Gonçalves. 2006. Parasitism of the mite ''Acarophenax lacunatus'' on ''Tribolium castaneum''. Pesq. Agropec. Bras., Brasília. 41(6): 1059-1061.

References

{{reflist Insect anatomy