An oak apple or oak gall is a large, round, vaguely apple-like

gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants. Plant galls are abnormal outgrowths of plant tissues, similar to benign tumors or war ...

commonly found on many species of

oak An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...

. Oak apples range in size from in diameter and are caused by chemicals injected by the

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 ...

of certain kinds of

gall wasp Gall wasps, also traditionally called gallflies, are hymenopterans of the family Cynipidae in the wasp superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1,300 species of this gene ...

in the family

Cynipidae Gall wasps, also wikt:gallfly#Usage notes, traditionally called gallflies, are hymenopterans of the family Cynipidae in the wasp superfamily Cynipoidea. Their common name comes from the galls they induce on plants for larval development. About 1 ...

Formation

The adult female wasp lays single eggs in developing leaf

bud In botany, a bud is an undeveloped or Plant embryogenesis, embryonic Shoot (botany), shoot and normally occurs in the axil of a leaf or at the tip of a Plant stem, stem. Once formed, a bud may remain for some time in a dormancy, dormant conditi ...

s. The wasp larvae feed on the gall tissue resulting from their

secretion Secretion is the movement of material from one point to another, such as a secreted chemical substance from a cell or gland. In contrast, excretion is the removal of certain substances or waste products from a cell or organism. The classical mec ...

s, which modify the oak bud into the gall, a structure that protects the developing larvae until they undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into adults. Some common oak-apple-forming species are the ''

Biorhiza pallida ''Biorhiza pallida'', also known as the oak apple gall wasp, is a gall wasp species in the family Cynipidae. This species is a member of the tribe Cynipini: the oak gall wasp tribe. Cynipini is the tribe partially responsible for the formation o ...

'' gall wasp in Europe, '' Amphibolips confluenta'' in eastern North America, and '' Atrusca bella'' in western North America. Oak apples may be brownish, yellowish, greenish, pinkish, or reddish.

Other galls

Considerable confusion exists in the general literature between the oak apple and the

oak marble gall ''Andricus kollari'', also known as the marble gall wasp, is a parthenogenetic species of wasp which causes the formation of marble galls on oak trees. Synonyms for the species include ''Cynips kollari'', ''Andricus quercusgemmae'', ''A. minor'', ...

. The oak marble is frequently called the oak apple due to the superficial resemblance and the preponderance of the oak marble gall in the wild. Other galls found on oak trees include the

oak artichoke gall ''Andricus foecundatrix'' (formerly ''Andricus fecundator'') is a parthenogenetic gall wasp which lays a single egg within a leaf bud, using its ovipositor, to produce a gall known as an oak artichoke gall, oak hop gall, larch-cone gall or hop st ...

and the acorn cup gall, but each of these has its own distinctive form.

Iron gall ink

Oak galls have been used in the production of ink since at least the time of the

Roman Empire The Roman Empire ruled the Mediterranean and much of Europe, Western Asia and North Africa. The Roman people, Romans conquered most of this during the Roman Republic, Republic, and it was ruled by emperors following Octavian's assumption of ...

. From the

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...

to the early twentieth century, iron gall ink was the main medium used for writing in the Western world. Gall nuts are a source of

tannin Tannins (or tannoids) are a class of astringent, polyphenolic biomolecules that bind to and Precipitation (chemistry), precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' is widel ...

in the production of

iron gall ink Iron gall ink (also known as common ink, standard ink, oak gall ink or iron gall nut ink) is a purple-black or brown-black ink made from iron salts and tannic acids from vegetable sources. It was the standard ink formulation used in Europe for t ...

. Tannins belong to a group of molecules known as polyphenols and can be taken from different parts of plants such as leaves, pods, fruits, and gall nuts. Along with gall nuts, other important ingredients in the production of iron gall ink include

iron sulfate Iron sulfate may refer to: * Ferrous sulfate, Iron(II) sulfate, FeSO4 * Ferric sulfate, Iron(III) sulfate Iron(III) sulfate or ferric sulfate (British English: sulphate instead of sulfate) is a family of inorganic compounds with the formula Fe2( ...

and

gum arabic Gum arabic (gum acacia, gum sudani, Senegal gum and by other names) () is a tree gum exuded by two species of '' Acacia sensu lato:'' '' Senegalia senegal,'' and '' Vachellia seyal.'' However, the term "gum arabic" does not indicate a partic ...

. The reaction between the tannins from the gall nut and the iron produces a complex that gives the iron gall ink its color. The gum arabic makes the ink more viscous and helps bind the ink to the writing surface.

Folklore

It is said that if a "worm" is found inside the gall on

Michaelmas Day Michaelmas ( ; also known as the Feast of Saints Michael, Gabriel, and Raphael, the Feast of the Archangels, or the Feast of Saint Michael and All Angels) is a Christian festival observed in many Western Christian liturgical calendars on 29 Se ...

, then the year will be pleasant and unexceptional, and if a spider is found, then it will be a bad year with shortages and ruined crops. If a fly is found inside, then it will be a moderate season, and if nothing is found, then serious diseases will occur all that year.Roud, Steven (2003). ''The Penguin Guide to the Superstitions of Britain and Ireland''. Penguin Books. p. 344.

Oak Apple Day Restoration Day, more commonly known as Oak Apple Day or Royal Oak Day, was an English, Welsh and Irish public holiday, observed annually on 29 May, to commemorate the restoration of the Stuart monarchy in May 1660. In some parts of England th ...

(or Royal Oak Day) is a former public holiday in

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

on 29 May that commemorated the Restoration of Charles II in 1660. The popular name refers to the event during the

English Civil War The English Civil War or Great Rebellion was a series of civil wars and political machinations between Cavaliers, Royalists and Roundhead, Parliamentarians in the Kingdom of England from 1642 to 1651. Part of the wider 1639 to 1653 Wars of th ...

when Charles hid in an

oak tree An oak is a hardwood tree or shrub in the genus ''Quercus'' of the Fagaceae, beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northe ...

. The commemoration persists in some areas today, although festivities have little to do with the Restoration.

Gallery

File:Oak apple BW 2014-11-16 20-35-06.jpg, An oak apple on an oak leaf. File:Andricus kollari oak marble gall, knikkergal.jpg, Oak apples File:Oakgall3800ppx.JPG, An

tree with multiple oak apples. Image:Oak Gall.jpg, ''Andricus kollari'' oak gall File:Galle.jpg, Oak apples on an oak tree. File:Gallrazorback.jpg, Oak apple gall on Garry oak (''

Quercus garryana ''Quercus garryana'' is an oak tree species named for Nicholas Garry, deputy governor of the Hudson's Bay Company. It is commonly known as the Garry oak, Oregon white oak or Oregon oak. The species is found in the Pacific Northwest, with a rang ...

'') File:Oak apples on oak leaf and in cross section.JPG, Oak apples on oak leaf and in cross section File:Biorhiza pallida male.jpg, ''

'' male

List of galls called oak apples

References

External links

Amphibolips confluenta

Biorhiza pallida

Gloucestershire Naturalists' Society photograph of galls with 'red apple' appearance
See also

The Oak Apple Gall
{{DEFAULTSORT:Oak Apple Cynipoidea