When I began this alphabetical countdown, I thought I might struggle with some of the letters but Q was easy: Quercus, the Latin for Oak tree. The mighty Oak features often in this blog: its leaves for their autumn colours, for the galls they support, for the insect larvae they feed, for the birds that nest in the Oak’s branches, for the fungi that grow beneath this amazing tree … and so much more. This year, amongst other topics, we’ve had Oak leaf burst; a new gall I was lucky enough to find; and some mothy goodness. I’m sure the Oak will provide further wonders in the future.
With heavy cloud and occasional rain, Sunday was not a day for finding butterflies in the woodland. So, I decided to look more closely at Oak leaves to see what I might find, and that strategy paid off in spades as the next few days’ blog posts will show. First up, I found a gall I hadn’t seen before, which turns out to be the sexual generation of the gall wasp Andricus curvator.
When the adult wasps emerge in the spring from the agamic (asexual) generation galls, which are formed on buds in the autumn and fall to the ground to over-winter, they lay their eggs mostly on Oak leaves but also, sometimes, on twigs or catkins, so these galls can take several forms. The ones I found (and they were numerous) were all on leaves, causing malformations and swellings, as you can see from the photos above and below.
I was tempted to split a gall open to see what was inside but it turns out I didn’t have to, as something had nibbled away at one gall, revealing a second round gall inside (see below). The larvae within this inner gall will emerge in the autumn to lay its eggs on Oak buds, and so the process will continue.
Here’s the latest in my occasional series of watching the trees come to life. This time, it’s the Oak tree – I’m not sure which of the Quercus species this is but I think they’re all fairly similar. First, the leaves burst from their buds, and the vibrancy of the new growth is dazzling.
And, of course, everyone knows acorns come from Oaks but perhaps, like me, you hadn’t noticed where the acorns come from. Below left are the male flowers, the catkins, dangling to catch the breeze that carries their pollen, and below right are the female flowers, tucked away, sheltered, waiting to be fertilised by the pollen and develop into acorns.
The key to where to locate this gorgeous butterfly, the Purple hairstreak, is in its scientific name Favonius quercus – quercus is the genus of the Oak tree – and I suspect that there are many more colonies of Purple hairstreaks living in our old Oak trees than we currently know about, as these butterflies spend much of their time unseen, high in the leafy boughs, feasting on honey dew.
There is a colony at Lavernock, and I’ve seen these butterflies at a couple of locations along the road that leads to Lavernock Point, but they were the only local sites I knew about. So, you can perhaps imagine my delight when, during Thursday’s walk at Cosmeston Lakes Country Park, I came face to snout with a female Purple hairstreak, which had ventured down to head height, and was happily running her yellow proboscis over the honey-dew-covered leaves.
This was the closest I’d been to one of these lovely creatures and had previously seen neither the purple sheen on their open wings nor the yellow proboscis. I was in butterfly heaven!
This must be the largest Oak apple gall I’ve ever seen – it was at least 1½ inches across, and it had attracted the interest of several small wasps, though these are not the wasps that created the gall in the first place.
I assumed that they were parasitic wasps about to use their long ovipositors to inject their own eggs into the gall, and it turns out my assumption was correct. Thanks to the British Plant Galls account on Twitter (@BritGalls), and to another Twitter user’s tweet, I’ve learnt that the tiny wasp in the photo below is a member of the Chalcis genus of wasps, probably one of the family of Torymidae. They are ectoparasites: their larvae feed on the larvae of the Oak apple gall wasp that created the gall in the first place.
I’ve been trying to find out how old these Oak trees are but haven’t managed it … yet. They grow on one side of the green that surrounds All Saints Church in Penarth’s Victoria Square. I did discover that the church itself dates originally from 1891, though it had to be rebuilt after being reduced to a burnt-out shell when 100 high explosives and 5000 incendiaries were dropped on Penarth during a bombing raid by the German Luftwaffe on 4 March 1941. I don’t know if the trees were also damaged in that bombing or whether they date from the 1890s … or even earlier. Whatever their age, they are magnificent.
If you’re a regular around here, you may recall that in August 2017, I posted a mini-series of posts about some of the galls you can find on Oak trees, which included the Oak Marble gall (see the post here). You might also remember that in late October, I was excited to discover a creature had hatched out of one of my galls and I initially thought it was the gall causer, a minute wasp called Andricus kollari. It was not – turns out it was one of the 29 other species of hymenoptera (bees, wasp, ants and sawflies) that can also be found living in an Oak marble gall (more on that here) (and I never did identify it).
Well, this time, maybe, just maybe, I have seen the gall-causing wasp itself, A. kollari. A while ago, while out walking, I found a small Oak sapling that was absolutely covered in marble galls and, when I found one that had no holes in it, I couldn’t resist bringing it home. The tiny wasp you see in these photos recently hatched out of this gall and the size of the hole it made, plus comparisons with online photos, has led me to think that this time I may have seen the gall causer. I couldn’t be one hundred percent certain of my identification without killing the wasp and getting an expert to check it but I didn’t want to do that. And, of course, I could be totally wrong yet again. In the meantime, the wasp has been returned to the area where I found it so, weather permitting, it can continue its life cycle.
Back in August, as part of a mini-series on some of the galls to be found on Oak trees, I posted about the Marble galls caused by the incredibly tiny wasp, Andricus kollari. Although most of the galls I’ve found have had tiny holes in them, meaning the wasps had already pupated and flown, a couple of weeks ago I found a couple with no holes. So, my curiosity got the better of me and I brought them home to see what might eventuate.
Note the tiny creature sitting on the gall.
Today, when I looked in the jar I’d put them in, I was so excited to see a tiny creature had appeared. Now, I initially thought this must be A. kollari, the gall-maker, but I was wrong … and, looking at images online, I don’t think I’m the only one who’s ever been fooled by this. However, with the help of friends who questioned and strangers who know much more than me, I’ve discovered there are at least 29 (twenty-nine!!) species of hymenoptera (bees, wasp, ants and sawflies) that might live within an Oak marble gall.
Though some of these critters simply use the gall for shelter, it seems that, for others, the gall tissue is a good source of nutrients, while still others are parasites whose larvae kill some or all of the larvae of the original gall-making wasp. Without detailed microscopic examination, I’m not able to determine which species this tiny wasp is but I thought you might like to see this little video of it performing its ablutions earlier. I have now released it back in the area where I found it so let’s hope it survives.
I can’t resist just one more post about oak galls, because I’ve just this week found one that’s not commonly recorded. So, today we have one that’s uncommon and one that’s very common. Let’s start with the former.
First identified in eastern Europe in 1859, the Ram’s-horn gall wasp, Andricus aries, has slowly been heading westwards and finally reached Britain in 1997. Since that first sighting in Berkshire, it has spread over much of southern England and into Wales. Though there are only a few records in the Aderyn database of Welsh biological records, two of my friends have also found Ram’s-horn galls in the past week so I suspect it’s more common that records suggest.
Like other gall-inducing wasps, Andricus aries lays its eggs on various species of oak and its larvae cause the oak to produce a gall, in this case with an elongated, sometimes spiralling shape, hence aries and its common name Ram’s-horn. Not much is yet known about this wasp, so if you see the gall, please do record it.
My second gall today is one many people will have seen, I’m sure, as its beautifully crafted silk-like button-shaped galls are very common on the undersides of oak leaves during the summer months. This gall contains the agamic generation (females needing no males to reproduce) of the Silk button gall wasp, Neuroterus numismalis. The galls fall to the ground in autumn and the larvae within pupate over the winter months. When the all-female wasps emerge in springtime, they lay their eggs on the edges of oak leaves and on the male catkins, where their larvae cause a different blister-shaped gall – that’s another one for me to seek out next spring. It is the female and male wasps of this second, sexual generation produced in the Blister gall that go on to mate and lay the eggs that result in the silk buttons. And so the cycle continues …
I know you’re all just dying to find out more about oak galls, right? RIGHT? I also know that I covered spangles in a previous post (see Currants & spangles here) but there are two different spangle galls to be found on the much be-galled oak tree: one is the hairy Common spangle and this is the second, the Smooth spangle gall.
This pretty little gall comes in combinations of pink and yellowish-green. It’s the work of Neuroterus albipes, a tiny wasp that you will probably never see, and inside each colourful saucer is a single larva that you will also probably never see. The galls drop to the ground in autumn and the larvae pupate over winter then female-only wasps hatch out in Spring to lay eggs that cause the entirely different Schenck’s gall (not one I’ve yet seen), from which male and female wasp hatch in the summertime. And so the cycle begins again.
This second gall, the Oyster gall, is also caused by a tiny wasp that has two distinct generations and forms two different galls. The wasp is Neuroterus anthracinus and the Oyster gall also contains the agamic generation of wasps (i.e. the females that need no males to fertilise their eggs). As you can see, these galls form on the veins on the undersides of oak leaves – once they’ve fallen to the ground, you can still see the two brown flaps of tissue where they were attached to the veins.
Once again, the sexual generation of wasps hatch in the Spring to mate and lay their eggs, this time in the buds of the oak tree, hence the name of the gall they produce: the April-bud gall. That’s another I need to look out for come the Spring.
earthstar 
You must be logged in to post a comment.