Tag Archives: oak galls

Andricus kollari, maybe

14 Saturday Apr 2018

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180414 Andricus kollari (3)

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.

Wild words: Inquiline

08 Wednesday Nov 2017

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I learnt this word the day a mystery wasp hatched out of an Oak Marble gall I’d brought home. Though I thought it must be the gall-causing wasp, it turned out that it was not and could, in fact, have been any one of 29 other species of hymenoptera that can, potentially, make their home in a Marble gall. According to an article I found on the Natural History Museum website (‘Oak-galls in Britain’ by Robin Williams), 21 of those other gall inhabitants are parasitoid (their larvae consume the original gall wasp’s larvae) and 8 are inquiline, which is to say that they are simply ‘exploiting the living space of another’ creature. And the Oxford Dictionary online actually gives the instance of ‘an insect that lays its eggs in a gall produced by another’.

171108 Oak marble gall inhabitants (1)

Of course, if I’d been smart and compared the size of the holes in other Marble galls I have to that of the newly emerged creature, I would’ve twigged that they must be quite different. I’m afraid my curiosity then got the better of me and I sliced in half one of the Marble galls I had, which means that the little creatures I exposed will not survive. The larva (and large hole) in the centre is the gall wasp Andricus kollari, and the little larvae and holes are representatives of the other 29 possibilities.

Lesson – and new word – learnt, I have now returned to the wild the other various galls, of several kinds, that I’d brought home thinking they were empty, in case they also have little creatures growing inside them!

Life in an Oak Marble gall

28 Saturday Oct 2017

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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.

171028 Oak marble gall

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.

Oak galls: ram’s-horns and silk buttons

18 Monday Sep 2017

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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.

170918 Neuroterus numismalis Silk button gall wasp (3)

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 …

Oak galls: spangles & oysters

09 Saturday Sep 2017

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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.

170909 Smooth spangle gall (1)

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.

170909 Oak Oyster gall (3)

 

Oak galls: marbles and apples

24 Thursday Aug 2017

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Though there are many more galls to be found on oak trees than the six I have covered in this and my previous two posts (knoppers and artichokes, and currants and spangles), I’ll make this the last lot for now. Otherwise, it might be just too galling for words!

170824 Andricus kollari Oak Marble gall (1)

So, to finish off this mini series, today we have Marble and Apple galls. Let’s start with the Marble galls and another tiny wasp, Andricus kollari, which lays its eggs on the twigs of any species of oak. This causes small perfectly round spheres to develop on these twigs. The spheres start off green but brown with age and will often remain on the twigs for a year or more. You can tell that the wasp has fled its larval home when you see tiny holes in the sphere. And although these do look just like brown marbles, I’m not sure you could use them to play the once-popular childhood game – they’re a little too light to shoot with.

And so to Oak apples. With their basic green colour and pink tinges, these do resemble immature apples but their surface texture and spongy feel are all wrong. The wasp Biorhiza pallida is the culprit this time, and these ‘apples’ contain several larvae, not just one.

Like many such wasps, both the Marble gall wasp and the Apple gall wasp have a sexual and an agamic (asexual) reproduction cycle. I have not seen the sexual galls produced by Andricus kollari which, interestingly, are produced only on Turkey oak (Quercus cerris) – the Marble galls are produced by the agamic (all female, no mating required) generation. Oak apple galls are produced by the sexual generation of Biorhiza pallida: the agamic generation lay their eggs on the roots of oak trees, so I haven’t seen those yet either.

170824 Biorhiza pallida Oak apple gall (1)

I find the whole concept of two different types of reproduction and, indeed, the way these wasps can cause such galls to form very intriguing!

Oak galls: knoppers and artichokes

23 Wednesday Aug 2017

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Following quickly on from yesterday’s oak galls, part 1, we have oak attack, part 2, a sorry tale of knoppers and artichokes – and, no, you can’t eat them!

First the knoppers, which are caused by Andriscus quercuscalicis, a wasp with chemical weapons. The wasp lays its eggs in buds on oak trees and the larvae, when they hatch, secrete a chemical that causes the developing acorn to distort into a knobbly lump, thus forming a home for themselves. The galls are structurally interesting but not so good for the oak tree, as the acorn is no longer a viable seed for the tree and I presume the knopper gall also makes the acorn unsuitable as food for wildlife as well. Apparently, this wasp only arrived in Britain in the 1960s but its spread has been rapid, with the galls now found throughout Wales and England and in southern Scotland, though only on the Pedunculate oak (Quercus robur).

Artichoke galls – also known as hop galls due to their resemblance to flower of the hop plant – are also the result of chemical distortion by a wasp. This time it’s Andricus foecundatrix that does the damage. Using its sharp ovipositor, it lays its eggs in the leaf buds of both the Pedunculate oak and the Sessile oak (Quercus petraea). Like yesterday’s Spangle-causing wasp, Andricus foecundatrix also has both a sexual and an asexual generation. The asexual wasp hatches from her artichoke home in the springtime and lays her eggs in oak catkins, causing a small oval-shaped gall to develop – I don’t yet have any photos of these galls but you can see images here.

One of Nature’s whodunnits

22 Thursday Sep 2016

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I sometimes get asked how I come up with enough ideas to post a blog every single day. This post goes some way to explaining how it works for me. I walk … a lot, and my camera is my constant companion, and I am by nature curious about … well, everything, really … and I’m also quite an observant person. So, for example, I went out for a wander around one of my local parks on Monday afternoon, thinking I would see if there were any fungi about, and also to get some photos of berries for a future blog. In the process of taking those photos, I noticed how many galls there were on this one particular oak tree so also took some photos of those … which then led me to check the neighbouring trees for galls. (If you’re not sure what galls are, there will now be a blog post on them as well!)

160922-whodunnit-1

When I got home and started going through my photos, this particular image really grabbed my attention because, for me, this is such a good example of one of Nature’s whodunnits. I look at this and my brain is immediately flooded with questions: how were these galls made? Why are they that shape? What is the creature that’s dead on the leaf? Is it a wasp? Did it make the galls? What killed it? It looks like it has white strands around it – a spider’s web or some kind of fungus? What created the bare patch where the leaf’s veins are showing? Was it the larvae of the wasp? What created the almost perfectly round hole in the leaf? Was that a leafcutter bee or something else? Was it the wasp? And what is the teeny weeny white thing? The shed skin of a larva perhaps?

I don’t know the answers to any of these questions … yet. But, if I find out and if I can get more images related to the story, the result could be a blog or three from just this one photo. And so it goes on …