Tag Archives: British galls

Acorns and galls

01 Sunday Oct 2023

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I was taking photos of acorns, thinking I’d perhaps write a blog about the many varied types of nuts, when it occurred to me how many galls I’ve been seeing on acorns this year. The gall-causers are having a good year.

230930 acorns (1)

I’ve covered these before (in Oak galls: knoppers and artichokes, August 2017) so won’t repeat myself here. But if you’re interested in what causes these particular galls, just click on the link to that previous blog. The galls in the first photo are Artichoke galls, caused by the tiny wasp Andricus foecundatrix, and the galls in the second photo, which have almost totally consumed the acorns, have been caused by another wasp Andriscus quercuscalicis.

230930 acorn galls (2)

Galls: Psyllopsis fraxini

12 Monday Jun 2023

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There is a place locally I call the secret field because it has just a couple of quite well-concealed entrances and very few people visit it – in fact, of the many local people I know there’s only one who knows this place. It is surrounded by large mature trees, which means the location is quite sheltered, and the field itself seems to have been planted with saplings perhaps 10-15 years ago, judging by their size. This secret field is where I make many of my most interesting discoveries, and this is one of the most recent.

230612 psyllopsis fraxini on ash (1)

These are galls on the leaves of Ash trees (upper leaf above, lower leaf below) caused by the larvae of a small bug called Psyllopsis fraxini, also known as the Jumping plant louse according to the Naturespot website, though I’m not sure that’s an official name. There are, apparently, three species of this Psyllopsis bug whose larvae cause galls like these so when recording such finds the aggregate name is used, Psyllopsis fraxini agg. You can read more about these wee beasties and see photos of the adult on the British Bugs website here.

230612 psyllopsis fraxini on ash (2)

Galls: Phytoptus avellanae

20 Monday Feb 2023

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These are my latest gall finds, caused by the mite species Phytoptus avellanae, shown here on Hazel (Corylus avellana) though they can also affect the buds of Filbert (Corylus maxima). The feeding of the mites on the plant cells within the buds causes those buds to swell and multiply. You can see a comparison in my photo below, the mite-infected gall bud on the left, the normal bud on the right.

230220 gall Phytoptus avellanae (1)

The mites that cause these galls are tiny, so rarely seen, but the Dutch Bladmineerders website has some excellent photos showing them in minute detail. As with so many galls, they are thought to be widespread in Britain but are not well recorded. So, if you’re out and about enjoying a spring walk and spot some Hazel, do please cast an eye over the buds, and record any galls you see. Citizen scientists really do make a difference to our knowledge of the natural world around us.

230220 gall Phytoptus avellanae (2)

Red, no danger

24 Friday Jun 2022

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Bright red in the landscape always draws my eye (witness Wednesday’s beetles), so this burst of vibrant colour on a low-growing rose bush immediately attracted me. And the fact that the rose was ‘persuaded’ to create this object by the larvae of a tiny wasp is really quite mind-blowing. That wasp is a Bedeguar gall wasp (Diplolepis rosae), and you may remember my somewhat haphazard but ultimately successful attempts to see one of these wasps when I kept a gall in a jar to see what emerged (Bedeguar gall wasp, May 2020). This time I’m restricting myself to admiring the wasp’s astonishing creation.

220624 bedeguar gall

Rose leaf galls

09 Thursday Jun 2022

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I was alerted to the possibility of finding these galls by a post I saw on Twitter – social media certainly is good for spreading the word about what to look for when and where.

220609 Blennocampa phyllocolpa

These galls, these downward rollings of the leaf edges on rose species, are due to the larvae of the sawfly Blennocampa phyllocolpa. Presumably, they cause the leaves to roll in order to create shelters for themselves, as the leaves seem otherwise unharmed, though, when I carefully unrolled perhaps 10 leaves, I only found a larva in one of them. The adult sawfly is a tiny black creature, photos of which you can see on The Sawflies (Symphata) of Britain and Ireland website. If you have roses in your garden, you may already be aware of this sawfly’s activities on your plants.

Holm oak gall mites

09 Wednesday Feb 2022

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During yesterday’s walk, when checking for leaf mines on the leaves of Holm oak (large numbers of Ectoedemia heringella present – you can see one in the photo below), I noticed a huge abundance of small bumps covering many of the leaves.

220209 Aceria ilicis on holm oak (1)

These are the galls caused by the miniscule mite Aceria ilicis. On the underside (though sometimes also on top), the depression in the leaf is filled with tiny brown hairs (an erineum) where the mites make their home. The galls can be seen throughout the year, so next time you spot a Holm oak, check out its leaves.

Oak: a new gall

25 Tuesday May 2021

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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)

238/366 Midge galls

25 Tuesday Aug 2020

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I was looking around at the various wildflowers yesterday at Cosmeston, seeing what insects might be about, when I noticed these odd growths on some of the Wild carrot flower heads. I split one open with my finger nail and a miniscule orange blob fell out; turns out that was the larva of a midge with the long-winded name of Kiefferia pericarpiicola.

200825 Kiefferia pericarpiicola (1)

The galls start off green (below left), before turning pinkish and eventually brown. According to the Nature Spot website, these galls can be seen from late summer through to autumn, after which the larvae will leave the gall and drop down to the soil to pupate. The midge only occurs in southern parts of Britain at the moment – and I only found two previous records in the Welsh biodiversity database – but perhaps that will change as our climate continues to warm and the midge flies further afield. It’s also possible, of course, that this insect is under-recorded – it seems the midge itself is almost never seen, only its gall creations.

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137/366 Bedeguar gall wasp

16 Saturday May 2020

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You might remember that, a few months ago, I posted about the (supposedly) empty galls of the Bedeguar gall wasp I’d found during a wet walk at Cosmeston Lakes Country Park (Empty pincushions, January 2020). A week or so after writing that post, I was back at Cosmeston and remembered to harvest one of the galls, which has ever since been sitting in a sealed jar on my kitchen windowsill.

Although the many holes in the gall made me think that all of its inhabitants had already hatched, I decided to wait and see if anything else appeared. Two days ago I noticed movement in the jar and, taking a closer look, found two different species of wasp had emerged.

200516 diplolepis rosae (1)

This is one of them, and I’m 99% certain this is the gall causer itself, the Bedeguar gall wasp, Diplolepis rosae, the offspring of the wasp that caused the gall to form in the first place. These wasps are so tiny – just 3-4 mm long – that most of us don’t usually see them so I was very pleased to have this one emerge from its gall.

200516 diplolepis rosae (2)

There is a bit of a story attached to the second wasp that emerged, and I am currently awaiting confirmation of its identity. As soon as I know more, I’ll write it up in a further post.