5
PLANT GALLS
Several members of the Field Club met at Epping Forest Conservation Centre on Sunday
7th August for a joint meeting with members of the British Plant Gall Society, led by
Jerry Bowdrey of Colchester Museum and Brian Spooner of Kew. I am not sure of the
final total, but it must have been in the region of 40 species for the Forest area.
It is always pleasing to get into the countryside on one of one's pet themes, and this day
was no exception; good weather, good company and much of interest, including some
tasty blackberries! (A report on this meeting by Jerry Bowdrey and Brian Spooner
appeals later in this Newsletter - Editor)
As I understand the distinction, plant galls arise from the interference by animal, plant or
bacterial life on the growth of a plant, producing distortion from the normal growth, and
not to be confused with wind damage, nor rubbing by animals, strictly not caused by
mechanical means.
For a field trip, there has to be restriction on what can be discovered, here, visual
searching of leaf, stem, shoot, inflorescence being the general locations, those organisms
causing damage to roots require much more detailed searching.
A simple to use handbook was provided by Blandford Press with their "Pocket
Encyclopaedia of Plant Galls in Colour", by Arnold Darlington and M.J.D. Hirons. The
revised edition was produced in 1975, but it is difficult to obtain from the second-hand
shops. Richmond Publishing produced "Plant Galls" by Margaret Redfern and R.R.
Askew as No. 17 in their Naturalists' Handbooks series, which I find a little more difficult
to use, thought the illustrations are splendid. The British Plant Gall Society's "Provisional
Keys to British Plant Galls" edited by F.B. Stubbs, is still obtainable at (I believe) £5, and
is very useful. For those wishing to involve themselves deeply, there are a number of
other books, most of which are difficult to obtain, however, a new book should come on
the market shortly, priced at about £70 - I have not yet felt interested enough to remember
the details!!
As is widely known, the oaks - Quercus robur and Q. petraea - are rich in the numbers of
invertebrates that they support, galls too find homes in these species, many caused by
Cynipid wasps, some by midges. One to look for is the currant gall on the male catkins,
caused by the Cynipid Neuroterus quercus-baccarum in the bisexual generation, this gall
also occurs on young foliage. The agamic generation forms the common spangle gall on
the underside of mature leaves.
Other galls on oak include the oak marble, at one time used in the production of ink and
dyes; another is the oak apple, a spongy mass on buds which in the agamic generation
forms brown lumpy tissues on roots as a result of oviposition - later the wingless females
migrate to the leaf buds where they lay parthogenetic eggs, which cause development into
oak apples.
Many galls are quite distinctive and easily identified. Amongst these are the agamic gall
of acorns, Andriscus quercus-calicis, the "Knopper gall"; the reddish "bean gall" of the
sawfly Pontania proxima on willow leaves, where the oval shaped galls may occur in
fairly large numbers or only singly. Another is the spiral gall of Lombardy poplar leaf
petioles caused by the aphid Pemphigus spirolhecae.