Saturday, 5 August 2017

Spot the Gall

Today I'm discussing the weird subject of galls. Galls looks like fruit or blight on a plant and are caused by the larvae of various species of wasp. The larvae release chemicals which cause the plant to produce odd looking appendages which the wasp larvae can then live in.

Galls occur on many different plants but are mostly commonly found on oak trees. Indeed, our native oak is the host plant for over 30 different species of gall wasps. I've seen lots of oak galls over the last few weeks and thought I'd discuss a few- incidentally these three were all found on the same tree.

First is an oak apple gall which is caused by the Biorhiza pallida gall wasp

Now oak gall wasps tend to have complex life cycles. They usually have alternate generations that are sexual with males and females followed by asexual generations with only females. Males and females of this wasp emerge in the summer and the females lay eggs on the roots of the oak tree. The asexual generation then produce galls on the roots from which females emerge in late winter to lay eggs in buds on the twigs, eventually leading to the formation of these galls. (Told you it was complex!)

This next one is an oak artichoke gall caused by the Andricus fecundator wasp.

This wasp lays eggs in the buds at the tips of shoots- the bud itself becomes greatly enlarged at this time of year. The next generation of wasps in Spring cause small galls on male catkins. 

Finally, this is a knopper gall formed by the Andricus quercuscalicis wasp

This wasp only became established in the UK in the 1970s. It lays its eggs in the developing acorns, causing the acorns to deform in this strange looking way.

It's easy to imagine that galls cause problems for the oak tree but other than reducing the number of acorns they have little effect. The galls wasps need the trees as part of their life cycle so it would be no good for them if their actions caused harm to the tree. 

There are galls wasps that use all sorts of different species of plants too. One I've seen is the robin's pin cushion gall caused by the Diplolepis rosae wasp

These galls are found on roses, usually wild ones. The wasp lays eggs in the buds of developing leaves which hatch into small white maggots. The maggots then secrete a chemical which causes these abnormal growths. 

Although they look soft and mossy on the outside they actually have hard woody structures in the middle which contain a number of chambers where the grubs develop. The grubs pupate overwinter inside the galls. Like with oak galls, this has very little effect on the plant. 

As I've been discussing weird growths today I thought I would also share a few fungi I've found this week. 

In the woods at Avon Heath there were fungi everywhere. 

I've struggled to identify this one to the species but I'm fairly sure it's a brittlegill, genus Russula.

Then there's this oddity which might be a misshapen jelly ear fungus (but I'm not certain at all!). 

Finally, an easy identification, a parasol fungus

Well I hope you enjoyed that dip into some of the weirder things of British nature. It'll be back to normality on Wednesday!

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