Galls (from the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

, 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

tissues, similar to

benign tumor A benign tumor is a mass of cells ( tumor) that does not invade neighboring tissue or metastasize (spread throughout the body). Compared to malignant (cancerous) tumors, benign tumors generally have a slower growth rate. Benign tumors have r ...

s or warts in animals. They can be caused by various

parasite Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson h ...

s, from

virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...

es,

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

and

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...

, to other

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

s and

mite 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 e ...

s. Plant galls are often highly organized structures so that the cause of the gall can often be determined without the actual agent being identified. This applies particularly to some insect and mite plant galls. The study of plant galls is known as cecidology. In human

pathology Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...

, a gall is a raised sore on the skin, usually caused by chafing or rubbing.

Causes of plant galls

Insects and mites

Insect galls are the highly distinctive plant structures formed by some herbivorous insects as their own microhabitats. They are plant tissue which is controlled by the insect. Galls act as both the habitat and food source for the maker of the gall. The interior of a gall can contain edible nutritious starch and other tissues. Some galls act as "physiologic sinks", concentrating resources in the gall from the surrounding plant parts. Galls may also provide the insect with physical protection from predators. Insect galls are usually induced 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. ...

e of the insects into the plants, and possibly mechanical damage. After the galls are formed, the larvae develop inside until fully grown, when they leave. In order to form galls, the insects must take advantage of the time when plant cell division occurs quickly: the growing season, usually spring in temperate climates, but which is extended in the tropics. The meristems, where plant cell division occurs, are the usual sites of galls, though insect galls can be found on other parts of the plant, such as the leaves, stalks,

branch A branch, sometimes called a ramus in botany, is a woody structural member connected to the central trunk of a tree (or sometimes a shrub). Large branches are known as boughs and small branches are known as twigs. The term '' twig'' usuall ...

es, buds,

root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...

s, and even

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechanis ...

s and

fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in partic ...

s. Gall-inducing insects are usually species-specific and sometimes tissue-specific on the plants they gall.

Indicator insects

Gall-inducing insect A gall-inducing insect is any insect that can cause the growth of galls within plants. There are several groups of insects that meet this description. They include the gall wasps, scales, gall midges, aphids, psyllids and certain species of ...

s include

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 ...

gall midge Cecidomyiidae is a family of flies known as gall midges or gall gnats. As the name implies, the larvae of most gall midges feed within plant tissue, creating abnormal plant growths called galls. Cecidomyiidae are very fragile small insects ...

s, gall flies (e.g., the

goldenrod gall fly The goldenrod gall fly (''Eurosta solidaginis''), also known as the goldenrod ball gallmaker, is a species of fly native to North America. The species is best known for the characteristic galls it forms on several species in the ''Solidago'', o ...

), Agromyzidae, aphids (such as '' Melaphis chinensis'', '' Pemphigus spyrothecae'', and ''

Pemphigus betae ''Pemphigus betae'', also known as the sugarbeet root aphid, is a species of gall-forming aphid that forms galls specifically on the commonly found narrowleaf cottonwood (aka the willow-leaved poplar tree), ''Populus angustifolia''. Sugarbeet ro ...

''),

scale insects Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than t ...

, psyllids, thrips, gall moths (e.g., ''

Epiblema scudderiana ''Epiblema scudderiana'', the goldenrod gall moth, is a species of tortricid moth in the family Tortricidae. As their common name suggests, they do feed on and form galls on goldenrod stems. To overwinter the caterpillars line the inside of their ...

''), and weevils. Galls produced by insects and mites include: *

Ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non-gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

flower gall: this gall is caused by a small mite that causes irregular distortion of male flowers. The galls are initially green, then dry and turn brown. * Ash midrib gall: normally long, these galls are succulent and have thick walls. A small cavity within each gall contains one or more small maggots, the larval stages of very small flies called midges. Female midges lay their eggs in very young leaflets during early spring. Gall formation begins soon after the eggs are laid. Specifics of the biology of this insect are not known. The galls probably do not harm tree health. * Elm cockscomb gall: these distinct galls, caused by an aphid, are about long and about high. The irregular edge of the gall and its red color at maturity account for the common name. The galls dry, harden and turn brown as they age. Aphids may be seen through a slit-like opening in the underside of the gall. This insect has a complex life cycle—it forms galls on elm in early summer, then feeds on grass roots later in the summer. The galls apparently do not cause significant harm to the tree. * Hackberry leaf gall: this gall is caused by a small ( long) aphid-like insect with sucking mouthparts called a jumping plant louse. The adults spend the winter under bark crevices and can invade houses in large numbers in the fall. Females lay eggs over a long period of time beginning when leaves begin to unfold from the buds in the spring. Feeding by the nymphs that hatch from these eggs causes abnormal plant growth that forms a pouch. The psyllids remain inside the galIs until they emerge as adults in late summer to early fall. There is one generation each year. Heavy infestations can result in premature leaf drop which over a series of years may affect tree health. *

Honeylocust The honey locust (''Gleditsia triacanthos''), also known as the thorny locust or thorny honeylocust, is a deciduous tree in the family Fabaceae, native to central North America where it is mostly found in the moist soil of river valleys. Hon ...

pod gall: this gall is caused by a small fly (midge). The sunburst cultivar appears to be very susceptible to this pest. Infested leaves have globular or pod-like distortions that contain one to several small maggots ( long). Infestations begin when females lay eggs in young leaflets. There are five or more generations each year. Infested leaves often drop prematurely and repeated damage can kill small branches. New shoots develop at the base of dead twigs. As a result, the natural shape of the tree may be lost. * Oak gall: see Oak apple * Petiole and stipule galls: thick globe-like galls can develop on leaf petioles and stems. Many of these are caused by insects called phylloxerans which are very similar to aphids. The hard, woody galls may remain on the tree for several years. Usually, there is one generation each year and the insects over winter on the tree in the egg stage. * Willow shoot galls: these swellings on shoots, twigs, or leaf petioles, may be caused by small flies (midges) or small wasps (sawflies). The gall increases in size as long as the immature stages are active. They cause no significant injury. The infestation may be reduced by pruning and destroying the galled areas before the adult insect emerges, usually in late summer. * Witchhazel gall: this gall is caused by an aphid that passes the winter in eggs laid on twigs of the plant. Feeding by the aphid causes the formation of conical galls on the upper side of the leaf. Each gall, produced by a single aphid, later becomes filled with offspring. Mature aphids with wings leave the galls in late spring and early summer and fly to

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' cont ...

. After several generations there, the insects return to witch hazel to lay the eggs that survive the winter. No galls are formed on the birch. * Banksia infructescence galls: microscopic Eriophyid mites ( Eriophyidae) commonly cause swellings on young infructescences of ''

Banksia integrifolia ''Banksia integrifolia'', commonly known as the coast banksia, is a species of tree that grows along the east coast of Australia. One of the most widely distributed ''Banksia'' species, it occurs between Victoria and Central Queensland in a ...

'' and '' Banksia marginata'' in south-eastern Australia Galls Banksia integrifolia2021

Fungi

RHODODENDRON FERRUGINEUM - GENTO - IB-137 (Neret)

Many rust fungi induce gall formation, including

western gall rust Pine-pine gall rust, also known as western gall rust, is a fungal disease A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familia ...

, which infects a variety of

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family (biology), family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanic ...

trees and

cedar-apple rust ''Gymnosporangium juniperi-virginianae'' is a plant pathogen that causes cedar-apple rust. In virtually any location where apples or crabapples (''Malus'') and Eastern red cedar (''Juniperus virginiana'') coexist, cedar apple rust can be a dest ...

. Galls are often seen in '' Millettia pinnata'' leaves and fruits. Leaf galls appear like tiny clubs; however, flower galls are globose. '' Exobasidium'' often induces spectacular galls on its hosts. The fungus ''

Ustilago esculenta ''Ustilago esculenta'' is a species of fungus in the Ustilaginaceae, a family of smut fungi. It is in the same genus as the fungi that cause corn smut, loose smut of barley, false loose smut, covered smut of barley, loose smut of oats, and o ...

'' associated with ''Zizania latifolia'', a wild rice, produces an edible gall highly valued as a food source in the

Zhejiang Zhejiang ( or , ; , also romanized as Chekiang) is an eastern, coastal province of the People's Republic of China. Its capital and largest city is Hangzhou, and other notable cities include Ningbo and Wenzhou. Zhejiang is bordered by Ji ...

and

Jiangsu Jiangsu (; ; pinyin: Jiāngsū, alternatively romanized as Kiangsu or Chiangsu) is an eastern coastal province of the People's Republic of China. It is one of the leading provinces in finance, education, technology, and tourism, with it ...

provinces of China.

Bacteria and viruses

Agrobacterium tumefaciens ''Agrobacterium radiobacter'' (more commonly known as ''Agrobacterium tumefaciens'') is the causal agent of crown gall disease (the formation of tumours) in over 140 species of eudicots. It is a rod-shaped, Gram-negative soil bacterium. Symptom ...

'' and ''

Pseudomonas savastanoi ''Pseudomonas savastanoi'' is a gram-negative plant pathogenic bacterium that infects a variety of plants. It was once considered a pathovar of ''Pseudomonas syringae,'' but following DNA-relatedness studies, it was instated as a new species. It ...

'' are examples of gall-causing bacteria. Gall forming virus was found on rice plants in central Thailand in 1979 and named rice gall dwarf. Symptoms consisted of gall formation along leaf blades and sheaths, dark green discoloration, twisted leaf tips and reduced numbers of tillers. Some plants died in the glasshouse in later stages of infection. The causal agent was transmitted by '' Nephotettix nigropictus'' after an incubation of two weeks. Polyhedral particles of 65 nm diameter in the cytoplasm of phloem cells were always associated with the disease. No serologic relationship was found between this virus and that of rice dwarf.

Nematodes

Nematodes are microscopic worms that live in the soil. Some nematodes (''Meloidogyne'' species or

root-knot nematodes Root-knot nematodes are plant-parasitic nematodes from the genus ''Meloidogyne''. They exist in soil in areas with hot climates or short winters. About 2000 plants worldwide are susceptible to infection by root-knot nematodes and they cause appro ...

) cause galls on the roots of susceptible plants. The galls are small, individual and beadlike in some hosts. In other plant species galls may be massive accumulations of fleshy tissue more than in diameter. Some ectoparasitic nematodes (nematodes that live outside the plant in the soil), such as sting and stubby-root nematodes, may cause root tips to swell. Nitrogen-fixing bacteria (''

Rhizobium ''Rhizobium'' is a genus of Gram-negative soil bacteria that fix nitrogen. ''Rhizobium'' species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells ...

'' species) cause swellings on the roots of most legumes (such as clover, peas and beans). These swellings, called nodules, are easily distinguished from root-knot galls by differences in how they are attached to the root and their contents. Nodules are loosely attached to the root, while root-knot galls originate from infection at the center of the root, so they are an integral part of the root. In addition, fresh ''Rhizobium'' nodules have a milky pink-to-brown liquid inside them, while root-knot galls have firmer tissues and contain female root-knot nematodes (creamy white beads less than in diameter) inside the gall tissues.

Other plants

Mistletoe can form galls on its hosts.

Uses

Galls are rich in

resin In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. Resins are usually mixtures of organic compounds. This article focuses on nat ...

s and tannic acid and have been used widely in the manufacturing of permanent inks (such as

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 ...

) and astringent ointments, in dyeing, and in leather tanning. The

Talmud The Talmud (; he, , Talmūḏ) is the central text of Rabbinic Judaism and the primary source of Jewish religious law ('' halakha'') and Jewish theology. Until the advent of modernity, in nearly all Jewish communities, the Talmud was the ce ...

records using

gallnut 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, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...

s as part of the tanning process as well as a dye-base for ink. Medieval

Arabic Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walter ...

literature records many uses for the gall, called in Arabic. The Aleppo gall, found on oak trees in northern

Syria Syria ( ar, سُورِيَا or سُورِيَة, translit=Sūriyā), officially the Syrian Arab Republic ( ar, الجمهورية العربية السورية, al-Jumhūrīyah al-ʻArabīyah as-Sūrīyah), is a Western Asian country loc ...

, was among the most important exports from Syria during this period, with one merchant recording a shipment of galls from Suwaydiyya near

Antioch Antioch on the Orontes (; grc-gre, Ἀντιόχεια ἡ ἐπὶ Ὀρόντου, ''Antiókheia hē epì Oróntou'', Learned ; also Syrian Antioch) grc-koi, Ἀντιόχεια ἡ ἐπὶ Ὀρόντου; or Ἀντιόχεια ἡ ἐπ� ...

fetching the high price of 4½ dinars per 100 pounds. The primary use of the galls was as a

mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains in ...

for black dyes; they were also used to make a high-quality ink. The gall was also used as a medication to treat

fever Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...

and intestinal ailments. The larvae in galls are useful for a survival food and fishing bait, as in the

Indigenous Australian Indigenous Australians or Australian First Nations are people with familial heritage from, and membership in, the ethnic groups that lived in Australia before British colonisation. They consist of two distinct groups: the Aboriginal peoples ...

foods bush coconut and

mulga apple The mulga apple is an Australian bush tucker food, often eaten by the Indigenous Australians of Central Australia. The mulga apple is in fact a combination of plant and animal; the insect gall grows inside the wood of the mulga tree ''(Acacia a ...

. Nutgalls also produce

purpurogallin Purpurogallin is an aglycone natural product. It is an orange-red solid that is soluble in polar organic solvents but not in water. Its glycoside (ether-linked to sugar), called dryophantin, is found in nutgalls and oak barks. Purpurogallin ca ...

. The gall of '' Rhus chinensis'', ''Galla chinensi'', has long been considered to possess many medicinal properties.Zhang, J.; Li, L.; Kim, S. H.; Hagerman, A. E., Lü, J. (2009). "Anti-cancer, anti-diabetic and other pharmacologic and biological activities of penta-galloyl-glucose". ''Pharmaceutical Research'' 26(9): 2066–2080. .

Gallery

File:Maple leaf gall.jpg, Gall on a

maple ''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since h ...

leaf File:Diplolepis-rosae.jpg, Rose bedeguar gall on a wild rose in summer File:Andricus foecundatrix Quercus01.jpg,

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 strobi ...

(''Andricus fecundator'') File:Gallwespe bedient sich Eichel2.jpg, Knopper gall (''

Andricus quercuscalicis ''Andricus quercuscalicis'' is a gall wasp species inducing knopper galls. Knopper galls develop as a chemically induced distortion of growing acorns on pedunculate oak (''Quercus robur'' L.) trees, caused by gall wasps, which lay eggs in buds w ...

'') File:Diplolepis Quercus02.jpg, Knopper gall (''Andricus quercuscalicis'') File:Eikengallen op mannelijke bloeiwijze.jpg, ''Neuroterus albipes'' forma ''laeviusculus'' File:Eucalyptus gall.jpg,

Eucalyptus ''Eucalyptus'' () is a genus of over seven hundred species of flowering trees, shrubs or mallees in the myrtle family, Myrtaceae. Along with several other genera in the tribe Eucalypteae, including '' Corymbia'', they are commonly known as ...

leaf gall File:Oak Gall.jpg, '' Andricus kollari''

oak gall Oak apple or oak gall is the common name for a large, round, vaguely apple-like gall commonly found on many species of oak. Oak apples range in size from in diameter and are caused by chemicals injected by the larva of certain kinds of gall w ...

File:Andricus kollari - Capanne di Marcarolo.JPG, ''Andricus kollari'' oak gall File:Gymnosporangium juniperii telial form.jpg, Gymnosporangium File:Oak marble galls 1.JPG, Oak marble galls, one with a gall fly exit hole and another with ''Phoma gallarum'' fungal attack File:Red-Pea gall Cynips divisa on Oak.JPG, Red-pea gall (''Cynips divisa'') on pedunculate oak File:Andricus lignicola - Cola-nut Gall.JPG,

Cola-nut gall Cola-nut gallsDarlington, Arnold (1975) ''The Pocket Encyclopaedia of Plant Galls in Colour.'' Pub. Blandford Press. Poole. . P. 155. develop as a chemically induced distortion of leaf axillary or terminal buds on pedunculate oak (''Quercus robu ...

s ('' Andricus lignicola'') on pedunculate oak File:Pineapple gall.JPG, Pineapple gall on Sitka spruce caused by '' Adelges abietis'' File:Developing Pineapple Gall.JPG, Developing pineapple pseudocone galls on Norway spruce File:Gall of Japanagromyza inferna in Centrosema virginianum L. - ZooKeys-374-045-g006.jpg, Gall of '' Japanagromyza inferna'' in ''

Centrosema virginianum ''Centrosema virginianum'' is known by the common names of Spurred Butterfly Pea, wild blue vine, blue bell, and wild pea. ''C. virginianum'' is a member of the family Fabaceae, it is identified by its trailing and twining vine and showy fl ...

'' File:Oakgall3800ppx.JPG, An oak tree with multiple oak apples File:Galle.jpg, Oak apples on an oak tree File:Eriophyes tilae tilae close up.JPG, Lime nail galls (''Eriophyes tiliae tiliae'') File:Rhododendron ferrugineum b.JPG, Leaf galls on '' Rhododendron ferrugineum'' File:Dasineura investita gall.jpg, '' Dasineura investita'' nettle gall File:Schizomyia impatientis galls.jpg, ''

Schizomyia impatientis ''Schizomyia impatientis'' is a species of fly in the family Cecidomyiidae. This gall midge species induces galls on jewelweeds in eastern North America. It was first described by Carl Robert Osten-Sacken Carl Robert Osten-Sacken or Carl-Robert ...

'' jewelweed flower gall File:Pachypsylla celtidisumbilicus gall.jpg, '' Pachypsylla celtidisumbilicus'' hackberry gall File:Neolasioptera boehmeriae crop.jpg, '' Neolasioptera boehmeriae'' false nettle stem gall File:Kokkocynips rileyi oak gall crop.jpg, '' Kokkocynips rileyi'' oak gall File:Phylloteras poculum oak gall crop.jpg, '' Phylloteras poculum'' oak galls File:Gall of peach tree leaves.jpg, Gall on peach tree leaves File:Bottle Tree Eucalyptus cypellocarpa.jpg, '' Eucalyptus cypellocarpa'' at The Gap Scenic Reserve,

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

File:Gall attack.JPG, Gall attack on

due to '' Leptocybe invasa'' at

Acharya N. G. Ranga Agricultural University Acharya N. G. Ranga Agricultural University (ANGRAU) is a public agricultural university with its headquarters at the village Lam, Guntur district, Andhra Pradesh, India. History The original Andhra Pradesh Agricultural University was esta ...

File:Actinidia polygama mushi.jpg, Fruit gall on ''

Actinidia polygama ''Actinidia polygama'' (also known as , silver vine, , and cat powder) is a species of kiwifruit in the Actinidiaceae family. It grows in the mountainous areas of Korea, Japan and China at elevations between . Silver vine can reach up to high ...

References

Notes Further reading * * *

External links

British Plant Gall Society

* ttp://www.bio.brandeis.edu/fieldbio/galls/galls.html Insect Galls ''Brandeis University''
Galls in Goldenrod, (''Solidago'')
* {{cite web , title=Common oak galls , work=University of Kentucky Entomology , url=http://www.uky.edu/Ag/Entomology/entfacts/trees/ef408.htm , access-date=2006-09-11 , archive-date=2006-09-13 , archive-url=https://web.archive.org/web/20060913044856/http://www.uky.edu/Ag/Entomology/entfacts/trees/ef408.htm , url-status=dead
Video footage of Scottish Galls