Autumn Galls

BEVERLEY AND DISTRICT U3A WILD THINGS Autumn 2020 This time of the year can be quite galling; in fact, it is the prime time to seek galls. These are a plant’s response to an invader that grows and eats inside the additional growth that the plant produces. Sometimes this additional growth is difficult to observe; sometimes it is quite prominent. Oak trees, unsurprisingly, have the greatest number of species of galling organisms. Turkey Oaks were introduced to Britain in 1735 as ornamental trees and since then, with the changing climate, continental species of Andricus wasp in particular, have expanded their ranges and taken advantage of the presence of the Turkey Oak. Eight species of Andricus wasp use these oaks for the sexual stages of their life cycles, they are heteroecious species, ie where sexual generations alternate with asexual generations. These are not like the yellow and black species that cause us problems in autumn. They are only a few millimetres long with a bulbous abdomen. The lives of the invertebrates that induce these growths can be bizarre. Knopper Gall Take the Knopper Gall (the brain-like growth on acorns of the Pedunculate Oak (they are very rare on Sessile Oaks)). These are produced in response to the presence of eggs and larvae of a tiny wasp, Andricus quercuscalicis, which arrived in Britain in the 1950s and is now very common. This gall is from the asexual stage and females emerge in spring, fly to Turkey Oaks and lay eggs in the developing male catkins. These galls are tiny and easily overlooked but, in May, males emerge first and sit on galls containing females waiting for them to bite their way out and be in the best position for mating. The mated females fly to Pedunculate Oaks and lay eggs in the newly-pollinated female flowers ensuring they are laid very precisely between the developing cup and acorn. Over time, the wasps may develop a slightly different strategy but, at present, they are reliant on Turkey Oaks to complete their life cycle. Marble Galls Another common species using Turkey Oaks is the Marble Gall (Andricus kollari); in fact it is probably the most common of any gall. Often mistakenly called an Oak Apple, it is hard becoming brown and has one chamber whereas the Oak Apple proper is soft and many chambered usually being red in part. The Marble Gall was introduced into Britain in the 1830s, from the eastern Mediterranean, as a source of tannin for leather working. The asexual females emerge from the gall in September and fly to the Turkey Oak laying their eggs between the tiny immature leaves inside dormant buds. These sexual galls develop slowly during the winter becoming apparent in March or April with the adults emerging in May or June. On the continent, this usually takes a year to complete but, in Britain, a proportion of the most populations take two years to complete the cycle. Oak Apple Galls are induced by the wasp Biorrhiza pallida and develop from a leaf bud in spring. It has varying amounts of red colouring. These are the sexual galls whereas the alternate gall occurs on shallow roots as spherical nodules. These are found on both Pedunculate and Sessile Oaks and occur throughout Europe and North Africa bordering the Mediterranean eastwards to into Turkey and Iran. Silk Button Galls (L) Spangle Galls (R). Red one Smooth Spangle Gall Other gall species do not use the Turkey Oak. One which has been very abundant this year is the Silk Button Gall Neuroterus numismalis (normally, Spangle Galls (Neuroterus quercusbaccarum) are more common in this area). To really appreciate this gall, it has to be viewed through a hand lens in direct sunlight. Doing this reveals a wonderfully delicate structure that really looks as though it’s finished with silk. Both these galls can often be found by looking under oak leaves that have a yellow spot on the upper surface. The life cycles of both are similar. Most females merge from the spangle galls in February and March, fly up to the canopy and lay eggs on the surface of leaves or catkins. These form either blisters on the leaf or a sphere on the catkin. The larvae pupate in the gall and adults emerge in late May and June. After mating, the females lay eggs on the underside of leaves next to a small cavity next to a vein and this is where the Silk Button Galls develops The Cherry Gall (Cynips quercusfolii) can be very impressive and be 15 to 25mm in diameter. Although it starts as yellow-green suffused with pink or red, it develops into a dark red sphere before turning brown. They are usually smooth if growing on Pedunculate Oaks but warty if on Sessile Oaks. These are not very common in our area but are so further s Away from oaks, a common gall on Crack Willows is the Willow Bean Gall (Pontania proxima) often seen as a red bean shaped growth right through the leaf. This is caused by a sawfly, different species of which lay eggs in different species of willow. Limes, particularly the hybrids and Large-leaved Limes are the Nail Galls (Eriophyes tiliae) these are often very common and bright red to 8mm tall. Lighthouse Gall Another upright gall is the Lighthouse Gall (Hartigiola annulipes) on Beech leaves. It has a domed end, is hairy and in some illustrations, these hairs look like the lines of light drawn by children drawing a lighthouse. Another gall to look out for on Beech is Mikiola fagi, a pointed, fusiform, pale swelling up to 10mm high. It has not been found in this country for may years but my lurk in isolated areas. Keep a look out. Sycamore trees have red galls of Aceria cephalonea usually less than 3mm high but often very numerous. These are induced by mites which are so tiny it is almost impossible to see them: we only know they are around by the galls produced. Wild rose is the host plant for the gall Robin’s Pin Cushion (also known as the Bedaguar gall). It has been fairly common this year and is induced by the wasp Diplolepis rosae. Wasps emerge in the spring in time to lay eggs in the newly-emerging buds. Males are vey rare so the females lay fertile eggs without mating. The gall is called “sleep apple” in Germany as it is said to aid sleep if placed under a pillow. The name Bedaguar derives from the Persian word for ‘wind brought’ and the name Robin refers to the English wood sprite Robin Goodfellow aka Puck This is a very small selection of galls to be found and the history and life cycles of the inducing organisms to be explored. It’s well worth the effort; there’s so much more to appreciate about our wonderful countryside with a little extra knowledge. A good place to start with galls is the Wild Guide “Britain’s Plant Galls”by Michael Chinery - ISBN 978-190365743-0. This is a photographic guide to some of the more common galls and is highly recommended. If you get hooked, or simply want to find out more, you could join the British Plant Gall Society www.britishplantgallsociety.org Mervin Nethercoat October 2020 .

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