Oak apple or oak gall is the common name for a large, round, vaguely apple-like gall commonly found on many species of

oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

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

larva A larva (; plural larvae ) 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. ...

of certain kinds of

gall wasp Gall wasps, also incorrectly 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 gener ...

in the family Cynipidae. The adult female wasp lays single eggs in developing leaf

bud In botany, a bud is an undeveloped or embryonic shoot and normally occurs in the axil of a leaf or at the tip of a stem. Once formed, a bud may remain for some time in a dormant condition, or it may form a shoot immediately. Buds may be spec ...

s. The wasp larvae feed on the gall tissue resulting from their secretions, which modify the oak bud into the gall, a structure that protects the developing larvae until they undergo metamorphosis into adults. 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 stro ...

and the acorn cup gall, but each of these has its own distinctive form. Some common oak-apple-forming species are the '' Biorhiza pallida'' 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.

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 ( la, Imperium Romanum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn Rhōmaíōn) was the post- Republican period of ancient Rome. As a polity, it included large territorial holdings around the Mediter ...

. From the

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

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 precipitate proteins and various other organic compounds including amino acids and alkaloids. The term ''tannin'' (from Anglo-Norman ''tanner'' ...

in the production of iron gall ink. 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 Iron(II) sulfate (British English: iron(II) sulphate) or ferrous sulfate denotes a range of salts with the formula Fe SO4·''x''H2O. These compounds exist most commonly as the hept ...

and

gum arabic Gum arabic, also known as gum sudani, acacia gum, Arabic gum, gum acacia, acacia, Senegal gum, Indian gum, and by other names, is a natural gum originally consisting of the hardened sap of two species of the ''Acacia'' tree, '' Senegalia se ...

. 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 some Western liturgical calendars on 29 September, an ...

, 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''. Pengun 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 t ...

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

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

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 (1642–1651) was a series of civil wars and political machinations between Parliamentarians (" Roundheads") and Royalists led by Charles I ("Cavaliers"), mainly over the manner of England's governance and issues of re ...

when Charles hid in an

oak tree An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...

. 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. Image:Oak apple Wiltshire October 2007.JPG, Oak apples on the undersides of oak leaves 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 of the Pacific Northwest, with a range stretching from southern California to southwestern British Columbia. It is commonly known as the Oregon white oak or Oregon oak or, in Canada, the Garry oak. It ...

'') 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, '' Biorhiza pallida'' male

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 Oak galls