Nature’s Master Builders

Last weekend we, as a family (minus two of the kids), visited The Lodge RSPB reserve in Sandy, Bedfordshire.  I had never been before, which is perhaps amiss of me as a birdwatcher as it is the headquarters of the Royal Society for the Protection of Birds or RSPB and only 45 minutes drive from home.

On arrival we were given a short introduction to the reserve at the visitor centre.  The beautiful heathland and woods were very quiet bird-wise we were told, but someone had just found a wasp spider in its web just earlier in the day.  We googled ‘wasp spider’ and discovered that this is a very striking, large spider (at least as far as the females are concerned) with, as the name suggests, yellow and black stripes on its abdomen.

Wasp Spider

A Wasp Spider – Argiope bruennichi – photo by Violart (Shutterstock)

We headed out along the reserve paths and, as predicted, the birdlife was very quiet and so we began to look for spiders.  It took a while to adjust my eyes – so used to scanning the treetops and skies for birds – to focus in on the gossamer constructions in between the foliage at knee height.  My daughter was far better at spotting the webs and we found many but sadly no wasp spiders.

What we did discover however was a world of tiny beauty often revealed by simply lifting a leaf.  Many webs did not at first appear to have spiders, but an inspection of the underside of adjacent leaves more often than not revealed the owner and hunter, hidden and poised to strike should the web do its work.

I had never walked through a nature reserve in quite that way before – pausing, stooping and cricking my neck to see what tiny worlds might be hidden just beyond my nose.  I might be a relative expert in the world of birds but here were new frontiers, unexplored and complex, whose intricacies I could not fathom.

Walking back towards the visitor centre we passed a number of young oak trees.  With our newly adjusted and fine-tuned eyes what had formerly appeared to be just oak leaves and acorns surrendered more to our vision.  Little brown balls, easily dismissed with just a cursory glance as acorns, turned out to be oak marble galls – the fruit not of the oak tree but of an insect:  a species of gall wasp.

oak-marble-gall.jpg

An Oak Marble Gall – home of the Oak Marble Gall Wasp Andricus kollari – showing the hole where the new wasp exited

Contained within these little spheres is one of the most astonishing works of nature you’ll come across – it has to do with one of the most efficient house-building schemes on earth!  We are all quite used to living in houses built using various materials sourced from far and wide involving many man-hours of labour, but the gall wasp takes house-building to another level.  By harnessing the growing power of trees they not only get the job done for them with materials they never had to find, but also ensure a well stocked larder within their new house!

Sometime in early spring, gall wasps inject their eggs into the developing buds of an oak tree effectively putting a deposit down on a house.  But this deposit is all that is needed for the work to begin and as the new wasp larva hatches so it stages a chemical takeover of the oak tree’s resources, hijacking the tree’s natural growth patterns and genetically altering them.  The result is that the tree grows a ‘gall’ that provides a safe home for the developing wasp and a supply of nutrients for it to eat.  In the case of the oak marble gall wasp this home is a little round marble-sized ball, initially green but browning as the summer goes on – it is after all part of the tree!

It is hard to imagine human engineering being capable of such a feat and builders would be out of work if a genetically altered plot of land produced a three-bedroomed house complete with fully stocked larder!  Parasites they may be, but I think the gall wasps have it figured out when it comes to providing a home for their young, and their galls do not appear detrimental to their host trees.

Oak Knopper Gall
The Knopper Gall – home of the Knopper Gall Wasp Andricus quercuscalicis on an acorn, showing the exit hole

As we discovered on our walk, it is a great time of year to look for these secret worlds of insects, be they webs or galls.  One of my favourites galls to look out for is the ‘robin’s pincushion’ gall – a fuzzy, red flower-like growth found on wild rose bushes and appearing to all intents and purposes part of the plant.  But don’t be deceived – it is the genetically modified home of yet another species of gall wasp – as flamboyant as any grand design, yet beautifully camouflaged!

To read this article as it appears in the Herts Advertiser please click here

Robin's Pincushion Gall

Robin’s Pincushion Gall – home of the Bedeguar Gall Wasp Diplolepis rosae on a wild rose bush

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