During our monthly forays into Reg’s Meadow we have noticed some interesting abnormalities in a number of plants, sometimes high up in tree branches, sometimes lower down on twigs, leaves and stems. Some of these were already familiar but we began to notice many more that were new to us, ranging in size from large, obvious abnormalities to tiny, easily-overlooked ones which can only be seen properly through a magnifying glass. Many of these are plant galls, a subject we knew very little about, so this has been a steep learning curve, but one that has proved fascinating (if you’re a self-confessed plant and insect “anorak”) and has provided a great crop of scientific names!

Galls occur as a result of the actions of a number of different gall-causers, which include viruses, fungi, bacteria, mites and other insects. These all interfere locally with a plant’s normal growth and development by releasing chemicals that cause the plant to react protectively, surrounding the area with an unusual swelling or distortion. The gall-causer lives inside the gall, uses its resources for food and shelter while growing to maturity, then bores its way out through a tunnel when it reaches adulthood. Many galls have elaborate shapes and colours and some can be very pretty. While galls sometimes look unsightly, they do not generally cause direct harm to the host plants, although serious infestations can become a problem, especially in plants which are used as food crops or for ornamental purposes. Here are the galls we have found in Reg’s Meadow so far, with some information about the insects which cause them.

Gall Wasps

Gall Wasps

Gall wasps are plant feeders of the family Cynipidae and cause galls on a variety of familiar plants, including wild roses, poppies, brambles and oaks. They are very tiny, mostly no larger than 3mm at most. They have a very complex reproductive cycle, which we won’t attempt to go into in detail, but which sometimes includes alternate generations of sexual and asexual females. Some species are entirely female and breed without any male assistance! This insect, which emerged from a deformed catkin I was examining, was around 2-3mm long and appears to be a gall wasp. Galls on Hazel catkins are usually caused by gall midges, but this is definitely not a midge. It may be what is called an inquiline, a sort of lodger or squatter, which uses old galls or other parts of a plant as a shelter during winter. The next two galls found in the meadow were definitely caused by gall wasps.

Young Gall	Mature Gall	Empty Gall

Robin’s Pincushions, which are also known as Bedeguar Galls or Mossyrose Galls are around 6-7cm in diameter and grow on wild rose bushes. They occur frequently in our meadow and you may have noticed them high up in the hedgerow behind the seating area. The name Bedeguar means “wind-brought” and comes through French from an originally Persian word. The female gall wasp Diplolepis rosae lays up to 30 eggs in developing leaf buds between May and July. Larvae hatch around a week later and tunnel into the young leaves, causing the leaf cells to respond by enlarging. By 4-8 weeks the gall is fully formed, with larvae growing in separate chambers. They are fully grown by late October and overwinter in the gall, emerging as adults which chew their way out.

Ram’s Horn Galls are caused by the gall wasp Andricus aries and are found on buds in oak trees. Not much seems to be known about the cycle of this wasp, except that it has two generations in the same year on the same tree. Eggs are laid in April, forming the gall from May, with adults emerging in August or September. The second generation are in the gall from October, emerging in early spring. This gall, found on the young oak tree in the copse near the hides in Reg’s Meadow, was an especially shapely example, elegantly curved and grooved, with its exit hole clearly visible. Sometimes more than one bud is affected and pairs of galls are formed.

Gall Mites

Gall mites are extremely tiny plant feeders, around 0.5mm in size. They are members of the Arachnid family, which includes spiders and mites, and are small enough to pierce and feed on individual plant cells, causing the surrounding cells to enlarge and multiply to form the gall. They are mostly members of the family Eriophyidae and often form minute pink or red pimples, mats or pouches on leaves of trees and shrubs, so small that they often go unnoticed unless seen through a magnifying glass. Most mite galls form in spring and early summer, while rapid plant growth is taking place. The mite causing the cluster of hairy pink galls pictured here is Eriophyes padi and these were found on blackthorn leaves in the older, right-hand hedgerow. This gall is often found on plants of the cherry family.

The larger galls seen here growing on the fruiting keys of the ash tree are also caused by a mite, Aceria fraxinivorus (alternative name Eriophyes fraxinivorus). The galls are irregular, woody encrustations, green at first and gradually turning to brown and black, which remain on the tree for up to two years. In Holland and France they are known as Cauliflower Galls. The mites are sap-sucking elongated cylinders, which apparently have no eyes, circulation or respiratory system and just two pairs of legs. They are mainly all female, producing eggs which need no fertilization.

Gall Nematodes

Nematodes are members of the Rhabditidae family and are tiny, threadlike, parasitic worms that often attack the roots of plants. In this case, however, the galls appear on the leaf-blade of Ribwort Plantain and the gall-causing nematode is Anguillula dipsaci (alternative name Ditylenchus dipsaci). The female lays 200-500 eggs and the larvae go through four “instar” stages, shedding their skins and growing larger ones as they increase in size and entering the young plant tissue at the fourth stage. Feeding breaks down the layers in the plant tissue and the galls form along the leaf. When the adult nematodes leave the galls through the exit holes visible in the photograph, they are then able to survive in the soil for up to two years without a host plant,  probably feeding on fungi, before beginning the cycle again.

Gall Moths

While the galls on the leaves of Ribwort Plantain are caused by nematodes, those in the flower spikes of the same species are caused by a micro-moth of the family Tortricidae. This moth is Tortrix paleana, described as having pale yellow fore-wings and grey hind wings. The female deposits her eggs, up to six at a time, in the flower spike and the plant reacts to surround the intruders with irregular growth. When we showed you “Mr Punch” in an earlier page we did not realise that this unusual shape was in fact caused by a tiny gall moth!

Picture-Winged Gall Flies

The last galls we found in the meadow are rather spectacular and grow on the stems of Creeping Thistle. These galls appear quite frequently on our meadow thistles and once you have noticed one, you seem to see them everywhere. The gall is caused by a small fly of the family Tephritidae, which are known as picture-winged flies because of the distinctive patterning on their wings. This fly is called Urophora cardui, which has markings like a letter M along each wing, and it produces gooseberry-like swellings on thistle stems. The female fly lays her eggs in the young stems and creamy-coloured larvae develop inside the gall which forms around them. This should be one of the easiest galls to notice when you walk round the meadow, so look out for them on thistles in late summer.

We hope to find further galls during our meadow monitoring walks. Quite a number are to be found on foliage, so we will keep hunting once the leaves appear and bring you more pictures of galls as we spot them.

Featured Tree – English (or Pedunculate) Oak (Quercus robur)

Oak is probably the best known and loved of all the trees in Britain and we have more than any other west European country. Even when not in leaf its silhouette is unmistakable, with its broad rounded shape and crooked twigs and almost everyone can recognize an oak leaf. A fully grown tree can reach around 100 feet in height and there are records of trees which measured up to 70 feet around the trunk. They can live for well over 500 years, especially when pollarded, and some have been estimated to be 1000 to 2000 years old. Some venerable old oaks are given names and have become tourist attractions, such as the Major Oak in Sherwood Forest, reputed to have sheltered Robin Hood and his men, though this tree is in fact probably no older than the 16^th century.

The name pedunculate means “stalked” and refers to the acorns, which grow on long stalks. The leaves are almost stalkless, (distinguishing it from the Sessile Oak, Quercus petraea which has stalked leaves and stalkless acorns). The scientific name Quercus is thought to come from the Celtic “Quer” meaning “fine” and “cues” meaning “tree” and robur means “strong” or “robust”. The common name oak is from Anglo Saxon ac and Old Norse eik, which mean “fruit” or “acorn”. Alternative names include Black Oak, Female Oak, Macey-tree, Tom Paine, Stalk-fruited Oak, Trail (referring to male catkins), Tanner’s Bark and Sussex Weed (because so many trees grow in that county).

In folklore the oak was held in high esteem throughout Europe, venerated in association with the supreme gods of the Greeks, Romans, Celts, Slavs and Teutonic tribes. The Druids held their rites and worshipped in oak groves and the name Druid is thought to mean “men of the oaks”, a Gaelic derivation of duir, their word for oak. Mistletoe was a potent and magical plant to Druids and often grew on oaks. Ancient kings wore crowns of oak leaves, symbolizing the gods they represented on Earth. The great respect for oak held by the Celts filtered through into the Christian religion, with many early churches being built near the sites of pagan oak groves. Carvings of oak leaves, acorns and even galls are found in many older parish churches and in most English cathedrals, sometimes openly displayed, often hidden away discreetly under misericords or high up in the roof. So-called “Gospel Oaks” were often significant stopping points in the ceremony of “beating the bounds”, which is thought to have originated in an ancient pagan practice connected to fertility rites!

Oak has excellent strength and elasticity and was much used in shipbuilding, giving rise to the phrases “Hearts of Oak” and “The Wooden Walls of England”, the ships protecting our shores from invasion. Charles II made the 29^th of May “Royal Oak Day” after his restoration in 1660, honouring the oak because he was supposed to have hidden in one while hiding from Cromwell’s men during the Civil War. The day was a public holiday and people wore oak sprigs and sometimes oak apples covered with gold leaf in honour of the Crown. An alternative name for this day is “Oak Apple Day”. A connection with royalty continues in Scotland, as the oak leaf is the badge of the Royal Clan Stewart.

The Celts believed oak to have the power to preserve youth, protect from lightning and cure toothache and bruised leaves were used to heal wounds.. Some medical properties of the tree have been known for many centuries but in more modern times the bark has been used to treat ague, haemorrhages, chronic diarrhoea, dysentry, bleeding gums, piles and sore throats, as well as being an alternative to quinine for treating fevers, when mixed with chamomile flowers. Powdered acorns and bark, mixed with milk, were thought to be an antidote for poison and snuff was sometimes made from powdered bark.

Other uses of oak bark include the tanning of leather and the making of dyes of various colours when mixed with other substances. Acorns were a traditional food for pigs over many centuries but they have also been used to supplement human food, especially in times of shortage, being dried and ground into flour or made into a coffee substitute.

Woodland was traditionally coppiced for many centuries and this opened up the canopy, allowing self-seeded trees such as oaks to thrive and grow tall. In recent times coppicing has largely been abandoned and this has meant that oaks do not do very well at regenerating in woods. Any which do begin to grow are either shaded out or predated on by insect caterpillars dropping down from the mature trees above, which strip them of their leaves, killing the infant trees. Seedlings have shallow root systems and cannot survive caterpillar attacks in the way that full grown trees are able to do. Young oaks thrive on railway embankments and other open spaces, where they receive plenty of light and are relatively free from predation. Birds and animals such as jays and squirrels help their spread by burying acorns in these areas.

Oak trees support an enormous range of insect life, with over 480 species that live on them having already been identified, more than any other tree in Britain. They also carry the widest range of different galls, all caused by gall wasps and a few of these are shown below. The photographs in this section were all taken in woodland in Surrey. The only example of English Oak in our meadow is still very young and has so far produced only one Ram’s Horn gall, as shown above.

Oak Galls Various	Ram's Horn Gall Andricus aries
Marble Galls Andrics kollori	Marble Gall + occupant!

The first photograph shows a selection of some of the galls to indicate their comparative size. (This photograph does not contain an Oak Apple gall, which is generally 2-3 times the size of the largest gall pictured). In the second photograph is another Ram’s Horn Gall, but not nearly as nice a specimen as ours!

Marble Galls are also known as Oak Nuts and sometimes wrongly called Oak Apples. They are caused by the gall wasp Andricus kollari and were originally introduced into Britain from the Middle East because the large amounts of tannic acid found in them was used for making ink. An exit hole is clearly visible, so I expected the gall to be empty, but when I cut it in half I found it to be still occupied, possibly by an inquiline re-using the gall. After rapidly taking the photograph I taped the gall back together, leaving the exit hole clear.....no gall wasps were harmed in the making of this page.....!

Oak Apple Gall Biorhiza pallida	Knopper Galls Andricus quercuscalicis

Oak Apples are home to the larvae of the gall wasp Biorhiza pallida. The female lays eggs in a leaf bud and they cause the tree to produce an apple-like growth, approximately 1.5 inches in diameter, with around 30 chambers, each containing one larva. Oak apples are generally found on trees in April or May.

Knopper Galls come from the wasp Andricus quercuscalicis and affect acorns. They have a two generation cycle and are usually found on trees in the same area as Turkey Oaks. The first generation adult wasps, all female, leave the galls in early spring and lay their eggs in Turkey oak buds. A sexual generation of male and female wasps hatch and mate, with the female returning to lay eggs on the English Oak. This wasp has only been recorded in Britain since 1962. The new galls are bright green at first, darkening with age.

Artichoke Gall Andricus fecundator	Cola Nut Gall Andricus lignicola

Artichoke Galls are swellings of the oak bud and scales and each contain a single larva of the gall wasp Andricus fecundator. The larva lives inside a smaller hard casing within the “artichoke”. An asexual female wasp emerges in spring and lays her eggs in oak catkins. These eggs hatch and develop into small oval galls which then produce the next, sexual adult generation of wasps ready to lay their eggs in the oak buds.

Cola Nut Galls caused by the gall wasp Andricus lignicola follow the same two-generation cycle as the Marble Gall wasp above, but while the cycle of the Marble Gall wasp is completed in one year, this wasp’s cycle takes two years, again alternating between English Oak and Turkey Oak.