NATURE: A mother’s work is never done

With another burst of rain blown over I walked into warm sunlight and the changing colours of autumn, to find the lakeshore a delicate mix of red and gold; the red from a glowing abundance of fruit, the gold as a bowl in which these rest.
Egrets have become a fixture here. Three years ago there was one, seen two or three times through the summer. This year we have three, two of which have bonded to become a pair. Next year they will breed and soon after we shall have a flock, dozens strong, and another flock, this of tourists come to see them.
A movement caught my eye and led me off course. There, on the bank at the side of the road, were a number of shallow, sandy mounds, each with a quarter-inch hole in the middle. Even before the question of ownership arose, an inch-long, glossy-black insect bearing bright yellow abdominal markings arrived on the scene.
A wasp. But not just any one, for this was Mellinus arvensis, the field digger wasp. As I watched, Ms Mellinus dived headfirst down the nearest hole. Knowing she must appear again, I settled to watch. It took a couple of minutes, but with the sun on my back I could rest there all day. My thoughts were drifting, alighting and lifting like so many snow-white egrets at the edge of a fish-filled shallow, then there she was, coming out of her burrow, bottom first, with a tiny piece of coarse sand held between her back feet.
She released her crumb and let it settle, marched rather proudly around her property, and went out of sight once more to continue her excavation. Only then did I notice a number of other digger wasps also at work. Some tunnels were out of sight amid vegetation and fallen leaves, while others were fully exposed. The entire colony consisted of dozens of these individual nests, the shafts of which might descend a full 12 inches into the ground.
At the bottom of each shaft is a nesting chamber, and within this the eggs are laid. The grubs are fed a diet of insects, which are actively hunted by the adult females. Once captured, these unfortunate prey animals are immobilised with a powerful venom administered by means of a sting, and carried to the waiting and voracious horde hidden underground.
I was able to observe this rather horrific behaviour for myself, and add my own notes here. 
As I watched, a number of other wasps returned to their respective burrows with various winged creatures, which they carried in their jaws. Amid this quiet carnage a large housefly-type insect, equally the size of the largest field digger, proceeded to walk over the spoil heap of the wasp I had been focused on. The fly was dabbing at the sand with its proboscis, as if it had found something it liked.
I looked away for just a second, and when I looked back the poor creature was upside down on its back, straddled by the spreading, yellow legs of its assailant. It showed no sign of life, nor made the least struggle to escape, and down the tube it went, no doubt to the dark joy of gluttony.
So what I want to know is this: Does the field digger wasp use some kind of pheromone or other attractant to draw prey insects to the vicinity of its nest, thus diminishing the need to hunt for food from afar?
A second question arises. A number of small black grassland ants were scouring the sand around wasp city, apparently untroubled by the presence of so many predators in full hunting mode. What do ants have by way of protection? Or would the wasps turn on these smaller creatures in more-straitened times?
I found myself wondering if a sting capable of immobilising a large insect within moments could pose some kind of threat to a curious human passerby, so Googled it on the spot. Digger wasps, apparently, remain placid unless provoked, at which point they are inclined to attack, daggers drawn and ready for the fight. Still, when one flew into my hair I felt it best  to withdraw. I shall be back though, this time with some kind of fly bait, that I might witness the real action.
Lastly, I should offer an apology to the very pregnant young lady who was more than a little startled at find a body lying roadside while on her walk. T’was only I, studying the habits of solitary wasps at work and at play, while dreaming of an egret horde. 
Michael Kingdon, a naturalist and keen fisherman, lives on the shores of Mayo’s Lough Carra, the best example of a shallow marl lake in western Europe and therefore an SAC of enormous ecological and conservation importance.