Trees of Sanctuary

I chose one of the children whose hands were raised.
“So, what’s the point of a wasp?” came back the question.
“Well, err.”
I was stumped for a few seconds. I’m not used to thinking about a species like that. In my world, species exist because they are genetically driven to pass on their genes to the next generation. They are honed by evolution to be supremely successful in their habitat space. If they fail, they die. No emotion, no mercy, no ‘point’.  My brain clicked into overdrive, skimming through mental files to find a response. ‘And why exactly did you get yourself into this one?’  I could hear myself asking in the background. A good question really.

It had all started as we arrived at school last week.
“You can’t go in through that gate. We have a wasps nest over the front porch entrance. It appeared overnight.”
Really? It must be tiny.
It all seemed a fuss about nothing.
“Do you want me to get rid of it?” I asked.
“Well, speak to the head. We’re trying to get someone out to it.” I was told.

I went round to the front of school through the other gate. We could see the wasp nest. It was beautiful. An ‘oh-so-delicate’, tissue paper globe, swirled with muted tones of greens, browns, reds, creams. Each stripe of colour represented a journey by the queen wasp from a source of wood, where she had chewed off tiny fragments using her strong jaws, to the nest where she had painstakingly spread the wood, mixed with saliva, layer upon layer to make up the structure. The nest I was looking at was definitely not the work of a single night.  But there was a reason this nest had gone unnoticed while it was being built; it was the work of a single female. She would have slipped backwards and forwards quietly, without drawing attention to herself.  That is, until today.

In social wasps, is it only the newly mated queens that survive through the winter. They find a place to snuggle down in a sheltered place, tuck away their antennae and wings beneath their body, and wait for the spring when they emerge to search for nesting sites. In this case, the favoured site was under the porch of the school. The queen will have begun by making a stalk or petiole. From this, she will have hung an umbrella shaped dome with hexagonal cells built into the underside of it, entrances opening downwards. Wasps do not have wax glands like bees, so the whole of the nest has had to be made from the paper generated from wood pulp. Covered with thin outer sheets of wasp paper, the comb this queen had built was hidden from view unless you peeped through the entrance hole at the bottom of the nest.

In social wasps, the queen lays her eggs in the comb, fixing them to the bottom of the cells. The eggs hatch into larvae and the larvae develop into the first worker wasps. It seemed the school nest was moving into this stage. The first workers were just emerging, and because there were several now trying to warm up on the school door in the cold morning, the nest had been noticed for the first time. I watched the paper dome. There was no activity round it. I knew the size of the nest, and could gauge the stage it was at. I would never have attempted to remove anything bigger, or a nest with activity going on around it, but rather than the wasp nest becoming a problem and leaving the children with a negative experience of wasps, I thought it was best for the nest to come down with minimum fuss. I popped a bag round it, detached the stalk from the porch, and carried the nest home.

By the time I got home, there was a buzzing coming from my bag. By lunch time I had released three wasps; without being able to see inside the nest, my guess is that they were newly emerging workers.  At this point, had the nest been intact, these workers would have taken over the building of the nest, the food collection and the job of tending the larvae, leaving the queen free to concentrate on egg laying. With the number of workers increasing, nests can begin to grow exponentially, perhaps producing 20,000 individuals over a single summer (though not all of these individuals will be alive at once).

I opened the nest I had brought home once all was quiet inside, cutting carefully round the stalk so I could remove the comb through the top of the paper dome. I wanted to be able to take the nest back to school, show the children the amazing engineering that created the nest, the beauty of it. I hoped the children would see that wasps are fascinating, understand their life cycle. Within the comb, there were indeed a few empty cells – some workers had emerged – but the whole cycle was there for the children to see. The outer ring of cells had tiny white eggs in the bottom, then moving in circles towards the middle, larvae – ranging from tiny at the the outside to huge, glistening white, writhing grubs towards the centre. Then there were the cells that had been covered with a white paper lid; these were the larvae in the process of becoming adult wasps. And then at the very centre were the now empty cells from which some of the worker wasps had emerged. The comb was incredible; perfect hexagons containing a study in the life stages of a worker wasp.

I took the nest into school and showed Amos’ class. It seemed to go okay – those that know me are used to my random enthusiasm for odd things, and wasps fitted into their topic for the term – mini beasts. Then I went to the older class, and that’s when the topic of ‘the point of wasps’ came up. Although I find wasps interesting, it’s the genetic perspective, not the natural history side, that I have concentrated on. I left the classroom aware that there was a hole in my wasp knowledge and set about fixing it.

One of the questions I had been asked was ‘what do wasps eat?’. I looked it up. The larvae of social wasps are fed on food that the adults have mashed up – insects, spiders, carrion, – but although the adults collect all this food for the young and have mandibles for the job, they don’t have the mouthparts to eat solid food. Instead, they suck up the saliva of the larvae which is rich is sugars; the sedentary larvae don’t need all the sugar they derive from their food. The adults will then top up with nectar from flowers. Wasps are good news to the gardener – they take pest insects to feed their larvae and act as pollinators when feeding themselves. One nest of 20,000 wasps could make a big difference to a garden.

Wasps are mostly problematic to us in the autumn. Towards the end of the summer, worker wasps are no longer produced. Instead a small number of special eggs are laid from which female queens and male wasps will emerge ready to begin the process of creating next year’s colonies. When there are no more larvae to be fed, workers drift away to find sweet food round our houses and orchards, coming into contact with us much more.

The whole social structure of these wasps is incredible, but when evolutionary success is dependent on how many copies of your genes penetrate into the succeeding generation, why would a system like this ever evolve? Why would individuals exist to look after their siblings rather than reproduce themselves? These worker wasps are apparently sacrificing themselves for the good of another individual. But all is not as it seems, and this is where I am back on familiar ground. It is true that the individual aims to perpetuate as many of their genes as possible in the next generation, but it does not matter which individual gets them there.

Social wasps are exhibiting something called kin selection, a theory first proposed by the geneticist WD Hamilton in 1964. The worker wasps are actually sterile females, all produced by a single queen. As is the norm in sexual reproduction, the queen passes approximately 50% of her genes to each worker offspring, but because of the unusual genetics of the male wasp that fertilised the queen (it has only one set of chromosomes, developing as it does, from an unfertilised egg), each of the sterile workers inherit 100% of the fathers genes. This results in workers sharing 75% of their genes with each other. We end up with the unusual situation where more genes of the female worker (75%) are passed on if she helps her mother raise more sisters, than if she has her own children who will only take 50% of her genes through to the next generation. How clever is that?

So I guess, in answer to the question about the point of a wasp, in my world wasps don’t have ‘a point’. They evolved in their habitat, intricately linked into a web of species, all co-depending in ways that we often fall short of understanding. Wasps, as they follow their drive to live and survive, are one of the building blocks of the pulsing, dynamic natural environment we live in. The wasp may not have been placed in this web of life and given a purpose, but that is not to say it has no value. Take away wasps and you lose vital pollinators, pest insect population controllers, food sources for other species. I’m not suggesting it would have been wise to leave a developing wasp nest above the entrance to a primary school, but I do suggest that if wasp nests appear in places they are unlikely to cause problems, tolerance is a good policy. The more species we knock out from our natural environment, the more likely it is that there will be a catastrophic collapse of the system that ultimately supports our own lives.

I always enjoy going back to the beginning, learning new things.  I love sharing the excitement of nature and evolutionary process with anyone who will listen.  And with these wasps, I was able to add one last thing to my story a couple of days after I brought home the nest. Another worker wasp emerged from the comb as I watched. For two hours I sat, as jaws worked to cut through the paper lid of one of the wasp’s cells. Antennae appeared, then a face and a leg. And from the face, I was able to identify the species of wasp that had started the nest in the first place; a yellow face with a single black dot in the middle, it belonged a tree wasp (Dolichovespula sylvestris). Unlike the common wasp which builds nests in holes in the ground, the tree wasp builds its nest on tree branches or bushes – hence the reason the nest was hung in the porch. I felt satisfaction. Another little piece of the jigsaw made sense.

As I watched the wasp fly away, I felt it and its genes had made an extra contribution on top of the pollination it will undoubtedly undertake. It had inspired me to learn more about wasps, and hopefully made a difference to the children’s understanding of wasps too. And somewhere out there, I hope the queen is rebuilding in a more secluded location so this wasps genes will move through to the next generation and so continue the success of the little nest that made such a positive impact on my week.