Another excellent and detailed focus by Julian upon the wildlife in our meadows and grasslands:

I’m sure we’re all familiar with above ground wasp nests, but way back in early August, I’d been alerted to the presence of an underground wasp nest beside the curving path down through our sloping field, by a collection of khaki coloured gravel chips at the entrance to an apple sized entry hole.The following day, sitting at our terrace table for our morning cuppa, I spotted the table surface was peppered with similar coloured, but much smaller accretions, which could be crumbled between the fingers to a soily dust.I’d never noticed this before, and then found the same material was present on the other tabletop, stone slab seats and even the car roof. The whole of the garden seemed to be a dropping zone! Surmising that the material came from the wasps, I set to with the camera, and quickly established that the wasps were indeed working really hard in numbers to remove this mud/soil from the nest.

It took a bit of effort to finally track down an explanation, and I’m including the video clip below to show the various stages of activity. As a wasp colony expands through the season, and these are (probably) the common wasp, Vespula vulgaris, the queen wasp that had chosen to build underground after emerging from hibernation, together with her worker progeny, have a design challenge.To expand the paper nest, (which is similar to the familiar ones we find in sheds and roof spaces), to accommodate the burgeoning number of larvae, the wasps need extra space. Rather like honey bees, which build their combs very exactly, leaving just enough space for 2 bees to pass on either side, wasps need to maintain about a 1 cm gap around the external surface of the papery nest, which hangs from a pedicel or stalk from the roof of the underground chamber. So they set to, with their strong mandibles to scrape away at the soil surface, wetting it with collected water mixed with saliva, to be able to mould a small pellet which they can then grab in their jaws and fly out from the nest. Presumably they fly these some distance away and drop them indiscriminately (?) to avoid drawing attention to the nest entrance.

This same nest had been ripped open earlier in the year by a predator, fox or badger I guess, drawn to the protein rich larvae. I’m sure that this mud dropping is a regular annual event here, and that this year’s continued dry spell at this time of the year, meant that the pellets hung around on surfaces for long enough for me to notice them. But something still perplexed me. Surely all these pellets couldn’t have come from the nest in the field nearly 50 metres away?

And so the day after our first set of garden visitors had enjoyed their walk round the meadow copse, I did an early morning walk round the paths, in part to be the first to physically snag and remove the many spider threads which always appear overnight, as above. As I looked up at the lovely morning mackerel sky, I was struck by a stream of insects just above head height. Too small for bumbles, and too early, at 7.00 am for this number of honeybees to be out and about. Tracking them back was easy. They were all emerging from a hole barely 2 metres off the garden path and taking the most direct route to gain height between the surrounding trees, were whizzing past my ear as I stood.

The necessary warnings were given to the day’s visitors and a suitable sign erected, and I’d be interested to hear from any readers who’ve observed this mud carrying. Googling You Tubes of underground wasps lead to a gamut of clips of enormous nests dug out from sites in the U.S.A. But the poor wasp, unlike the honeybee, has a very poor and inadequate press, and it took me ages to find this UK site, The Big Wasp Survey, and the work of Professor Seirian Sumner (SS). There’s much of interest here about the huge benefits of having wasps in a landscape or garden; a very useful identification guide to the different British species; and also the tantalizing prospect of a soon to be published, UK based book on their ecology, by SS, which seems to be way overdue.(see the later update!)

I’ll be more reluctant to destroy their nests in future, though in the case of this Tree wasp, Dolichovespula sylvestris, nest, expanding in early summer beside an upper window in desperate need of painting this year, there seemed to be little alternative. Though there always is, isn’t there?

After keeping regular watch on these 2 underground wasp nests by early November, all activity had ceased. I waited another week, then on a dry day decided to excavate them, since as with bumblebees, the colony completely collapses at the end of each year.

In each case I was amazed by just how large the structure was, and in spite of the torrential downpours at the end of October, just how dry and intact they were.In each case the nest seemed to be offset from the main entrance, with a dog leg in the access mouse/mole/vole tunnel, and suspended by a stalk from the roof of the domed cavity.

The exterior of the nest was a sheeted laminar form, similar to the appearance of above ground nests, but inside the larger than football sized nest, the hexagonal cell structure was just as precise as the wax made honeycomb found inside a honeybee hive.With parallel sheets of cells held apart, or possibly even suspended in horizontal planes by a fairly regular series of narrow pillars, a bit like the supports in a multi-story car park.

Initially I was certain that in the larger nest, these sheets were constructed horizontally, but the in-situ torch illuminated photo of one of the nests possibly suggests otherwise. Perhaps I’d rotated the whole structure to manipulate it out of the hole, intact?No matter, this was a superbly constructed home, requiring, I estimate, around 25 to 30 kg of soil to have been mined and removed from site, by the wasp workers as the colony expanded in late summer, using the frequent mud carrying sorties, described above.

A little bit of reading revealed more differences about the social wasp lifecycle, Vespula vulgaris, its survival strategy, and its differences with honeybees. The bees are obviously capable of overwintering as a colony, in large part because of their ability to make and store honey as an overwintering food store in their waxcomb cells. They also produce a special caste of worker bee with larger body fat stores at the end of autumn, and are able to form tight clusters within the hive over winter, to conserve heat. The single, fertile, mated queen survives in the middle of this cluster, although she stops egg laying until the worker bees begin to find fresh pollen and nectar sources and bring these into the hive in midwinter. This is still a risky strategy, and every year many “wild” colonies will fail to survive to spring. In addition, the honeybee larvae are fed, largely with a pollen based food, and complete their metamorhphosis within a pupa, inside a cell capped with wax by the workers.

The social wasp underground nest will have been begun in early spring when an overwintered, hibernating mated queen wasp emerges and begins her quest to find a suitable location to begin her new colony. At which point it’s worth asking why build underground? To do so, commits to a potentially wetter, more humid, and cooler space with the added effort involved in mining out the cavity. Equally it might create a safer space and a more stable temperature range than experienced in any above ground location.

The queen will build the early cells from harvested wood fibre, in her own form of  papier-mâché, and into these she’ll lay eggs destined to become (female) worker wasps. Whilst collecting mainly nectar from flowers, and honeydew secretions from aphids as her own food, she provisions each of the larval cells with collected invertebrates. These are typically aphids, spiders, caterpillars, flies, for these common wasps, which are the protein rich animal food the larvae require to develop. Apparently no pollen, or indeed honey/nectar, is used as wasp larval food. Another interesting aspect in the evolutionary history of wasps is how they carry this food back to the nest. Sometimes whole, sometimes chopped into pieces, using their strong mandibles, and using a variety of strategies to physically move the bugs into their nest. The earliest and most primitive wasps just dragged them backwards, along the ground, a technique still used by some solitary wasps. However gradually, different species developed the ability to carry food either in their mandibles, or suspended beneath their bodies and grasped by their legs.

The first larvae which will have been nursed and supported by the solitary queen, take around a month to develop, pupate and emerge from a silken spun cocoon which they spin in their open topped, uncapped cell. Once the first workers have emerged, they begin to take on other nursing and management behaviours within the nest as well as foraging for food, including the unusual proctodeal trophallaxis, which involves the nurse wasps consuming the sugary excreta produced by younger wasp larvae. No waste here! Meanwhile the queen is now able to concentrate on egg laying, with around 200 to 300 per day being laid.

As a result the colony can now grow in size very rapidly, but towards the end of the season, the queen concentrates on laying different, fertilised eggs which will develop into new queens, and also eggs destined to become drones/males, so that the majority of the larger cells in the huge sheet above, were probably occupied by future queens, since in a large colony over 2,000 will be produced! The largest comb of cells measured around 11 inches in diameter, and contained roughly 40 X 50 cells across. At this stage one can imagine just how many invertebrates are being collected from the locality, and it’s been estimated that across the UK, over 14 million Kgs of invertebrates are caught by common wasps annually – a hugely valuable natural pest control service.

The emerged, sexually active virgin queens and males mate, and then eventually the mated queens look for suitable hibernating locations for the winter, the old queen dies, and with no new workers to replace the workforce, the existing colony collapses. It’s very unlikely, currently, that a colony would survive the winter in the UK, though this can happen in warmer climates.

Click here for more wasp facts from The Natural History Museum, pending the publication of Sirian Sumner’s upcoming book titled “Endless Forms – Why we should Love Wasps“, now due for publication in April 2022. For those who can’t wait, here’s a really superb lecture by the incredibly enthusiastic Professor Sumner, given earlier this year, explaining why we should all become wasp lovers! And do listen to the Q&A for even more great insights into the world of wasps from a world expert.

The existing wasp nest being entirely made of paper, would probably (if I hadn’t dug them up!) degenerate and be recycled by other invertebrates and fungi within a few months.

Which has given me much food for thought as we continue with our own personal decluttering drive, about the ecologically brilliant circular economy of these social wasps. Spending all that time and effort constructing these amazing structures, undergoing massive population explosion, exploiting the natural resources all around and in so doing limiting the population of other potentially damaging invertebrate species. Then as food supplies dwindle, sacrificing the vast majority of their number in inevitable planned mortality, with the hoped for regeneration the following year, once conditions and food supplies become favourable once more.

I hope you’ve all learned something new about wasps from this, as I did in researching the subject. In particular, for anyone late cutting or strimming an area of grassland, be aware that nests of this size could lay hidden. When cutting our main meadow this yar, I was aware as I started to turn the hay, that a sole, large (queen) wasp, was quartering a particular part of the field, obviously looking for its burrow/nest entrance. I was clearly lucky that I’d cut the hay fairly early in July. By late August just imagine how many workers might have been incensed by my activity!

Equally I take it as endorsement of the number of prey invertebrates in the vicinity, that 2 such large nests could prosper so close to each other.

Posted by Julian Wormald