Oak: a new gall

25 Tuesday May 2021

Posted by sconzani in insects, leaves, spring, trees

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Andricus curvator, British galls, galls on Oak leaves, galls on oak trees, Oak gall wasps, oak galls, oak tree

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.

210525 Andricus curvator (1)

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.

210525 Andricus curvator (4)

268/366 Gone galling

24 Thursday Sep 2020

Posted by sconzani in insects, trees

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Common spangle gall, gall wasps, galls on oak trees, Knopper gall, Marble galls, oak galls, Oyster gall, Silk button galls, Smooth spangle galls

I wanted a relatively short walk between rain showers so headed to a small local green belt where Oak saplings were planted a few years ago, and my wander turned into a challenge to see how many different types of gall I could find in just this one small copse of young Oaks. The answer? Six!

First up, Knopper galls, caused by the wasp Andriscus quercuscalicis. For more on that gall, see my August 2017 post Oak galls: knoppers and artichokes.

Next, Marbles, which I covered in Oak galls: marbles and apples, August 2017.

Then, I found some Common spangles (below left), caused by the wasp Neuroterus quercusbaccarum. More on that mouthful in Oak galls: currants and spangles, August 2017.

You may have noticed my photo of Marble galls also had something else on the leaves. These were Smooth spangles (above right), a product of the wasp Neuroterus albipes.

I covered both Smooth spangles and this next gall, the Oyster, in the same blog: Oak galls: spangles and oysters, September 2017. The photo on the left above shows Oysters just beginning to form on the spine of the leaf; the one on the right shows two more developed examples, both on the same tree.

And, last but most certainly not least, as there were thousands of these on all the Oak trees I looked at, Silk button galls, caused by the wasp Neuroterus numismalis. I wrote about those in Oak galls: ram’s-horns and silk buttons, September 2017.

Not a bad haul for an hour turning over leaves and peering amongst branches. I didn’t find examples of all the Oak galls I’ve found before but I was very happy with this sampling.

116/366 A gall and its parasites

25 Saturday Apr 2020

Posted by sconzani in insects, nature, trees

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Chalcis wasp, Oak apple gall, Oak apples, oak galls, oak tree, parasitic wasp, Torymidae

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.

200425 oak apple gall

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.

200425 parasitic wasp

155/365 A good crop of apples

04 Tuesday Jun 2019

Posted by sconzani in 365DaysWildin2019, insects, nature, trees

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Tags

Biorhiza pallida, gall wasps, galls, galls on oak trees, Oak apples, oak galls, Pedunculate Oak

190604 oak apples (1)

But you wouldn’t want to eat them! These are oak apples, the incredible creations of the larvae of the wasp Biorhiza pallida. By a magical process of chemical interaction, the larvae force the buds of the Pedunculate Oak to change and produce these galls, which the larvae call home until they’re ready to develop into their next stage of life.

A couple of the young oak trees in some fields near where I live are proving particularly attractive to these wasps so they have a bounty of apples growing on them this year. Yet another of Nature’s miracles!

190604 oak apples (4)

Andricus kollari, maybe

14 Saturday Apr 2018

Posted by sconzani in insects, nature, trees

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Andricus kollari, gall wasps, galls, galls on oak trees, Marble gall, oak galls, Oak Marble gall, oak tree

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

Posted by sconzani in insects, nature

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#WildWords, Andricus kollari, gall wasps, hymenoptera living in Marble gall, Inquiline, Marble gall, oak galls, Oak Marble gall

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

Posted by sconzani in insects, nature, trees

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Andricus kollari, gall wasps, galls on oak trees, hymenoptera in Oak marble galls, hymenoptera living in galls, Marble gall, oak galls, oak tree

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.

171028 Wasp living in Oak marble gall (1)

171028 Wasp living in Oak marble gall (2)

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

Posted by sconzani in insects, nature, trees

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Andricus aries, gall wasps, galls on oak trees, Neuroterus numismalis, oak galls, oak tree, Ram’s-horn gall wasp, Silk button gall wasp

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.

170918 Andricus aries Ramshorn gall wasp on oak (1)

170918 Andricus aries Ramshorn gall wasp on oak (2)

170918 Andricus aries Ramshorn gall wasp on oak (3)

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 …

170918 Neuroterus numismalis Silk button gall wasp (1)

170918 Neuroterus numismalis Silk button gall wasp (2)

Oak galls: spangles & oysters

09 Saturday Sep 2017

Posted by sconzani in insects, nature, trees

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gall wasps, galls on oak trees, Neuroterus albipes, Neuroterus anthracinus, Oak gall wasps, oak galls, oak tree, Oyster gall, Smotth spangle gall

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

Posted by sconzani in insects, nature, trees

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Andricus kollari, Biorhiza pallida, gall wasps, galls on oak trees, Marble galls, Oak apple galls, Oak apples, oak galls, Oak marbles, oak tree

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.

170824 Andricus kollari Oak Marble gall (2)

170824 Andricus kollari Oak Marble gall (3)

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.

170824 Biorhiza pallida Oak apple gall (3)

170824 Biorhiza pallida Oak apple gall (2)

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)