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
Eusociality ( Greek 'good' and social) is the highest level of organization of sociality. It is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generations wit ...
insects such as
termite
Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...
s,
bees and
ant
Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...
s, in which the abdomen swells in order to hold enlarged
ovaries
The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...
, thus increasing
fecundity
Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the capability to produc ...
. 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
''Macrotermes'' is a genus of termites belonging to the subfamily Macrotermitinae and widely distributed throughout Africa and South-East Asia. Well-studied species include ''Macrotermes natalensis'' and ''Macrotermes bellicosus, M. bellicosus.'' ...
'', 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
termite
Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...
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
Arthropods are covered with a tough, resilient integument, cuticle or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. T ...
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 (SB), sometimes called stingless honey bees or simply meliponines, are a large group of bees (from about 462 to 552 described species), comprising the Tribe (biology), tribe Meliponini (or subtribe Meliponina according to other aut ...
species have physogastric queens, such as the South American species ''
Paratrigona subnuda'' and ''
Schwarziana quadripunctata''.
Physogastrism can also be seen in the stingless bee species ''
Melipona bicolor
''Melipona bicolor'' , commonly known as Guaraipo or Guarupu, is a Eusociality, eusocial bee found primarily in South America. It is an inhabitant of the Araucaria moist forests, Araucaria Forest and the Atlantic Rainforest, and is most commonly ...
'', which is facultatively
polygynous
Polygyny () is a form of polygamy entailing the marriage of a man to several women. The term polygyny is from Neoclassical Greek πολυγυνία (); .
Incidence
Polygyny is more widespread in Africa than in any other continent. Some scholar ...
, 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 gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...
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 Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
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 beetle family Chrysomelidae, commonly known as leaf beetles, includes over 37,000 (and probably at least 50,000) species in more than 2,500 genera, making it one of the largest and most commonly encountered of all beetle families. Numerous s ...
(e.g., ''
Gastrophysa'') and
Meloidae (e.g., ''
Megetra'').
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) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as ea ...
(ticks and mites) have physogastric females, sometimes involving precocious development of offspring inside the mother's body.
See also
*
Neosomy
References
{{reflist
Arthropod anatomy