Nature Notes from Skye
(and occasionally other places)
Fri 16 - Sun 18 Sep 2005 Doncaster (Part 2)
Galls on Oak
On the left, the Silk Button Gall (Neuroterus numismalis) with a few Common Spangle Galls (N quercusbaccarum) at the base of the leaf. Centre: Smooth Spangle Gall (Neuroterus alpibes). On the right is a Common Spangle Gall parasitised by the hyper-gall-causer Parallelodiplosis galliperda, a gall-midge which causes the original gall to bulge up and increase in size. The dark smudge on the left of the spangle is a sign of the hyper-gall.
Left, the Knopper Gall, Andricus quercuscalicis, which forms a hard ridged structure on or around the acorn. Centre, the Marble Gall, Andricus kollari, which originates from a bud. Right, the similar but smaller and rougher Cola-nut Gall, Andricus lignicola.
The Oak Artichoke Gall, Andricus fecundator, swells the bud and its scales. A less noticeable bud swelling, but with a tell-tale exit hole, is caused by Andricus corruptrix. The woody swelling on the twig in the RH pic is the work of Andricus inflator.
Staying on a woody theme, here's the Oak Callus Gall, Andricus quercuscorticis, on the bark, the Barnacle Gall, Andricus testaicipes, at the base of a sapling, and the Truffle Gall, Andricus quercusradicis, taken from the root.
The elongated lower bud in the left-hand picture is galled by Andricus solitarius. The centre pics show the Pea Gall, Cynips divisa, and the Striped Pea Gall, Cynips longiventris. The bud with the exit hole is still being investigated but it may be Callirhytis bella.
All the galls shown so far on this page (though not the hyper-gall) are made by members of the gall-wasp family Cynipidae. The insects themselves all look pretty similar, and their larvae even more so, but the galls they make show extraordinary variety. There are a great many others made on oak by this family - the ones shown here are just those found on three short walks in the Doncaster area. Also many of them have two or more generations, each making completely different galls on different parts of the tree.
Now a couple of galls with the causers themselves clearly visible. The first is a scale insect of the genus Asterodiaspis, which causes pits in the surface of the twigs. Of a similar shape, but unrelated, is nymph of the jumping plant-louse Trioza remota, which causes part of oak leaf to bulge upwards and lives in the depression on the underside.
Finally a couple of galls caused by gall-midges (Cecidomyiidae). Macrodiplosis dryobia causes a downward fold of a leaf lobe, while Macrodiplosis volvens causes an upward roll of the leaf margin between the lobes.
Part 3 consists of galls on other kinds of trees and bushes.
All photos and other content copyright © Carl Farmer