BrownhillsBob's #365daysofbiking

On a bike, riding somewhere. Every day, rain or shine.

Posts tagged ‘parasite’

#365daysofbiking How do you like those apples?

May 3rd – An interesting surprise to note one tree near Clayhanger Common this year has been hit heavily by the gall wasp that causes oak apple galls.

These growths – protective structures grown from corrupted leaf buds – house gall wasp larva that will eat their way out of the gall as the season progresses. The corruption is caused by the parent wasp injecting the larva’s egg into the nascent leaf bud covered in a chemical that causes the cells to deform.

It’s one of the odder evolutionary parasitic actions I’ve ever come across and it fascinates me. And it doesn’t seem to affect the tree at all.

One of the more peculiar aspects is all the oak trees around the one affected are completely untouched. But this one is affected more heavily than any I’ve ever seen in my life. There must be several thousand oak apples.

But why just this one tree? A fascinating thing.

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#365daysofbiking Sick more?

September 5th – Whilst I obsess over galls on oaks and wild roses, other shrubs and trees have their own problems. Here on Clayhanger Common, this sycamore tree is affected by sycamore mites and tar spot fungus.

The curious leaf growths form on the leaf like a gall from the point at which mites feed on the leaf by the same mechanism that other gall insects imply – in the case of these tiny mites, their saliva corrupts the lead cell DNA to grow into a gall.

On the underside of the leaf, a tiny, fur lined aperture into the gall is used by the mite after it has grown to lay its eggs, and the gall is eaten by the hatchling.

This leaf also has tar spot fungus.

Neither harm the host tree to any extent.

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#365daysofbiking From tiny acorns grow


August 1st – The various varieties of wasp gall that form on oak trees are necessarily seasonal. Rosy, marble and apple galls form from wasp eggs injected into leaf notes, so grown from them in spring and early summer, and by now are largely vacated and spent.

Knopper and artichoke galls form from eggs laid in acorn buds, corrupting the fruit into a gall from the crop, so don’t start appearing until late summer. Right now they’re developing well, forming a protective, curiously shaped home for the wasp larva to hatch in and develop.

Galls are fascinating things for sure, and are markers of the passing year.

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#365daysofbiking Flown

July 8th – The galls that formed on the oak trees in spring that looked like rosy apples have now served their purpose and are dead, their bodies spongy and containing many holes where the wasps that grew from larvae within ate their way out to freedom and maturity.

Galls fascinate me: Corruptions of the tree’s buds by a parasitic, tiny wasp, they grow as host to the wasp’s offspring and take many forms.

These expired galls signal the passing of the season and soon we’ll start seeing knapper and artichoke galls which form on acorn buts, but have the same genesis.

Parasites are fascinating.

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#365daysofbiking From mighty oaks

May 3rd – It’s always interesting to watch the variety and spread of oak galls on the trees I pass.

At the moment, rosy red oak apples are developing well, corrupted from leaf buds by the tiny wasp who laid her egg in the bud. Her larvae will hatch inside, done on the inside of the gall and drill their way out when mature.

Fascinating things that don’t harm the tree and continue a millennia old relationship between oak and parasite.

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#365daysofbiking The rise and gall:

September 12th – I’ve been watching the robin’s pincushion gall I found in Darlaston mature as the weeks pass by. I’m interested to see if it shows any sign of being vacated by the insects who grow inside it, and also observe how it decays, to find out what’s under the ‘fur’.

It’s grown redder, and the fur seems to be dying away, with a cavity open on the upper side. I wonder if the wasps have left?

These creations of parasites – unique to wild and dog roses – are absolutely fascinating and I’ll be keeping an eye on this one as autumn draws on.

September 11th – I had promised no more wasp galls. Sorry, just one more I missed. 

I’ve been looking at this type of gall for ages and not realised what they are – a small, coffee-bean sized growth, caused by genetic mutation provoked by an injected tiny wasp’s egg. These small, rough galls are tiny compared to the more familiar marble oak galls which are smoother  and rounder.

They function in the same way though, as a growth pod and foot source for the wasp larva that hatches within, and when ready, the wasp will eat it’s way out to freedom.

This poor tree at Darlaston had knapper galls, marble galls, common galls and cola nut galls. And plenty of acorns!

August 14th – Sorry, after this I promise no morale oak wasp galls!

This is an artichoke oak wasp gall, created the same way as all the others, this wasp selects acorn buds, which are corrupted into these neat little artichoke shaped growths to house it’s larvae.

These examples spotted on Clayhanger Common.

That’s it now, I think we’ve collected the set…

August 13th – More oak wasp galls, which I’ve gone all out to find this year for no other reason than they fascinate me.

On a small sapling by the canalside track at Hopwas, hundreds of thousands of almost annular, ring-like growths on the leaves, looking maybe like fungus or some odd egg. These are the delightfully named common spangle gall for the flat ones, and silk button galls for the rounder, more sharply defined ones.

These are all created by the same mechanism – a small wasp injects an egg into the leaf, and a chemical coating the egg disrupts the plant DNA to grow the gall, which leaves a light patch on the upper surface of the leaf where nutrients have been leeched away by the larva growing underneath.

I’m not sure why galls like this captivate me so much but they are absolutely fascinating.

August 10th – Oak galls continue to fascinate, and on this tree in Victoria Park, Darlaston, there’s quite a display of knopper galls, the first I’ve seen this year.

Like other oak parasites, the knopper wasp lays eggs in it’s host, secreted in a chemical that corrupts the cellular DNA of the host plant matter causing the gall too grow. In this case, the target is the acorn itself, and on this tree, one can see some acorns blighted by two such galls.

As with others, the egg hatches and ithe wasp larva eats the gall and grows safe in it’s corrupted acorn, before boring it’s way out when mature.

Also on this tree, the more conventional wasp gall – the common ‘oak apple’ of folklore, a spherical gall grown the same way.

These galls don’t harm the host, but do reduce the functional acorn crop. I’d love to know just why the oak is targeted so particularly with the and not so much other trees…