TIM KAYE, of Wiltshire Wildlife Trust, takes a closer look at nature's odd protrusions

NATURE has the ability to delight us, inspire us and provide us with innumerable comforts but it is the ability to surprise and disgust that sometimes catches our attention.

When out walking who hasn’t thought what that weird swelling mass on that plant is? It could be a massively inflated thistle stem or a round marble structure on an oak leaf.

These are all galls and they are a fascinating addition to our wildlife and a reminder of the tenacity with which some organisms survive.

Galls are simply an abnormal growth produced by a plant under the influence of another organism.

A good example is the Robin’s pincushion which looks like a furry red ball and is the result of a small gall wasp, Diplolepis rosae, which chemically injects the plant with its eggs and induces tissue that surrounds them as they grow.

Not only does the plant provide protective tissue for the growing grub but it also forms nutritive tissue which sustains up to 60 young as they develop.

The plant is always Dog or Field Rose and only one per cent of male wasps have ever been found, the female reproducing by parthenogenesis.

Other parasitic wasps have been known to lay their eggs within the growing larvae of the Robins pincushion wasp and there have even been other parasites known as hyperparasatoids which lay their eggs in them.

Fully formed adults emerge in May after which the pincushion begins to look a bit brown and sorry for itself.

Galls like this tend to form on less robust plants or ones growing on poor soil conditions and one gall does not kill the plant outright.

The Robins pincushion wasp is named after Robin Goodfellow, the woodland sprite who is also known as Puck. It is so noticeable that Cicely Mary Barker decided to paint one as part of the Flower Fairy series. Another name for it is the Bedegar, from the Persian for “wind-brought”.

Most galls are not as obvious as this one but many are specific to certain plants.

If you know the plant then you have narrowed down what type of gall it is.

It is not only insects that can cause them; fungi, viruses and bacteria also induce all manner of strange swellings.

The cluster of dense twigs on Downy Birch can be caused by a fungus Taphrina betulina and are known as “witch’s broom”.

Also notable are the galls produced by wasps which produce apple-like swellings known as Oak apples. It even has its own day on May 29 which celebrates the restoration of Charles II. This relates to the English Civil War when he hid in an oak tree.

So, when you are out and about, take a closer look at those odd protuberances and give thought to the small lives that are lived out unnoticed by us.