Resisting the obvious pun is surely a sign of my growing maturity, but I will readily admit to a total ‘immaturity’ when it comes to knowing much about galls. I photographed the charmingly-named ‘Robin’s Pinchushion’ (also known as the ‘Bedeguar Gall’) below in 2010 but aside from discovering that it was caused by the larva of the tiny gall-wasp, Dipoloepis rosae, I really hadn’t learnt much more about galls until I started looking for them this year.
It turns out there are hundreds of the things. Some are caused by mites or aphids, some by Cynipidae gall wasps and Cecidomyiidae gall midges, and yet others by sawflies. Still more are the result of infections by bacteria, fungi, or nematodes and are difficult to tell apart from insect-caused galls. Most (I’m not sure if that could be ‘all’) are caused by irritation and/or stimulation of plant cells due to infection, or feeding or egg-laying by insects. Why should a plant react like this to another organism? It’s actually the result of a symbiotic relationship between the plant and the ‘attacker’: the galls provide shelter for the developing organism, but at the same time they restrict potential damage to the plant to a relatively small area allowing the plant to mostly develop and reproduce normally.
Something I also hadn’t previously appreciated is that each type of gall-producer is specific to a particular kind of plant, and each gall is characteristic of the causal organism: ie if you can identify the plant the gall is growing on then there’s a very good chance that with a little bit of research you’ll be able to identify what is making the gall.
From a panrecording POV (or purely out of natural history interest of course) galls, therefore, are irrefutable evidence that certain organisms are living on site. And that’s pretty helpful, because I’ve not actually seen (or maybe just not identified) any of the adult forms of the gall producers below. And while the following is a rather small list so far, it’s a start – and now that I know a little more about what to look out for I’m sure I’ll discover many more galls at the wonderful Great Chalfield in the coming years…
- Caused by the gall mite Eriophyes tiliae these Nail Galls (normally up to 5 mm long) develop on the upper surface of Lime tree leaves, usually on Common Lime. The mites move onto the foliage in the spring, having overwintered in the bark crevices or around buds, and as they suck sap from the leaf surface the chemicals released cause the galls to develop. The mites (and the galls) are very common and widespread in Britain wherever Limes grow.
- Difficult at first to even recognise as a gall, this growth is caused by the tiny orange bodied, long legged gall midge Jaapiella veronicae. Adult females lay their eggs in the terminal buds of speedwells, most commonly (as here) Germander Speedwell Veronica chamaedrys. This causes the young leaves to become thickened and deformed allowing a pouch to develop inside which the larva/e develop. The galls can be very common and the midge is widespread across much of Britain.
- These are the galls formed by the larvae of the gall wasp Liposthenes glechomae on Ground Ivy Glechoma hederacea, a very common plant in the mint family. Ground Ivy is an important nectar source in Spring, and its culinary and medicinal uses were the cause of its being exported to America – along with the wasp presumably as both are now widespread there – by early European settlers.
- The two ‘Kidney Bean Galls’ above were photographed on a Crack Willow that we planted in our garden two years ago. It’s made by the larva of the Willow Redgall Sawfly Pontania proxima, a small, all-black sawfly that I may or may not have seen in the garden: if I have seen it I certainly didn’t recognise it! The female sawfly inserts an egg into the leaf tissue where it hatches and begins to eat. This stimulates the leaf to produce this distinctive gall, which is bean-shaped, smooth and emerges equally on both sides of the leaf. Common and widespread in Britain, identification was confirmed by the County Recorder John Grearson.
- Common on Field Maple Acer campestre the Red Pustule gall is formed by the evidently abundant mite Aceria myriadeum. It’s certainly very common here at Great Chalfield, though whether the mite itself has ever actually been seen is another matter altogether…
- The rather bizarre Robin’s Pincushion (named for the sprite Robin Goodfellow apparently, not the bird) is a gall caused by the larvae of the tiny wasp Dipoloepis rosae. It is widespread and common, and can be found developing on the stems of wild roses during late summer. The grubs inside the gall feed on the host plant throughout the winter and emerge in spring as adults. There is a fascinating account of the life history of the wasp and the formation of the gall on Wikipedia.
For more about galls have a look at:
- British Plant Gall Society: http://www.british-galls.org.uk/
- Naturespot: http://www.naturespot.org.uk/taxonomy/term/19701
All photographs copyright Charlie Moores/Talking Naturally 2012