Mass Gatherings

MASS GATHERINGS

At this time last year, on a quiet warm evening, one of the most striking moth sightings we have seen was a lek or mating gathering of Ghost Moths.  The satin white wings of the males shimmered in the twilight as many scores of them made their swaying flight about eighteen inches above the flower meadow . More and more appeared, but within twenty minutes they were disappearing as they searched and found the brown winged females resting in the herbage below.

Flower meadow where lek occurred at twilight

 

Mating Ghost Moths

A few summers ago when camping on the South Brittany coast, we saw another mating flight, also at twilight. Hundreds of Cockchafers  were in lumbering flight just over the tops of willow bushes growing at the head of the dunes. Again this lasted for little more than half an hour before they too disappeared.

Even more dramatic than the mass flighting of winged ants we sometimes see in Britain, like the one that happened simultaneously in many parts of the country in thundery weather last summer, is the flighting of winged termites in the tropics.

I quote from our log: Sep.3^rd 1995.    Barkley Tableland, West Queensland:

“Yesterday we decided to stop on these wide open grasslands so we left the road and drove down the fenceline  for a way, and made camp.  

It was still 94F and the oppressive heat unbearable so in desperation at about 5pm we walked back along the fence to make the air move around us a little. The van soon looked a forlorn dot in the vast straw-coloured plain. Walking back to the van, before we disturbed a big mob of Brahmin cattle crowding round a water tank fed by a clanking windmill, we noticed we were making a sheltered shadow for great clouds of flying termites. There were two kinds, one with a fat pale orange body, and others which were small and black. Female and male? They were pitching in great numbers on our backs and when we got back to the van we were staggered by the vast swirling cloud of them in the lee of the van. Huge numbers had drowned themselves in our water bucket and bowl where I’d put the spuds I’d peeled for the evening meal. They got in our eyes, our noses, ears, mouths, and they drove me into the van where I spent the next half hour slaughtering them. Tony cooked the one-pot I’d got ready and by twilight they had gone.

A few big fat drops of rain fell from the heavy  dark cloud above.

This morning there was a brisk northerly wind  carrying the smell of rain on damp earth; .....somebody had been lucky. Perhaps  this was what had triggered the termites’ flight yesterday.”

Termite plain

Mass emergences are always amazing.

Many years ago we were in a small town on the banks of the Loire and we saw the gutters and nooks and crannies between the buildings were full of piles of the corpses of Mayflies. We must have just missed the fabled flighting of these insects, but years later when on a boat in one of the many waterways making up the delta of the Danube in Romania, we saw another sort of Mayfly emerging from the slow-flowing water.

 I quote from Tony’s entry in our log:

“We happened upon a considerable natural phenomenon: swarming Giant  or Long-tailed Mayflies (Palegenia longicauda) One of the party had spotted a few to start with. They were flying, keeping pace with us and then dropping back to start again, low over the muddy water. But then, over the next hour or so, numbers increased  until there were untold scores of thousands, and the water surface was thick with them. Passengers and crew were hanging over the side in wonder. Danny our co-leader shouted to Mary to bring her net and by hanging precariously well over the side he managed to bring a specimen aboard. He needn’t have bothered as the swarm became a cloud and they were crash-landing on us, on the deck, like stranded flying fish.

Long-tailed or Giant Mayfly, Danube Delta

The body was about two inches long, with black eyes, a pale cream thorax, grey body and two  yellow tail streamers, about two inches long in the males and a bit shorter in what we took to be the females. Their wings were opaque and almost silver, quite short and rounded.

Small  flocks of Terns and Starlings were feeding on them in a couple of places as we motored slowly along the streamway between a thick fringe of willows. I watched a Little Egret catching any that came within reach as it stood on a log and waited. The Starlings were a bit like a Peregrine in a flock of pigeons ; they didn’t know which one to go for as they hawked through them. “

Giant Mayfly emerging from the water

These Mayfly , the largest in the world, are apparently rare now, occurring in only a few rivers in Eastern Europe.

Once when camping in woodland in SW Australia we noticed oily-looking black patches several feet across, on the thin herbage all around us. Looking closely we saw these patches were formed by myriads of small black flies, crowded so closely there was no ground to be seen between them. The oily effect was due to the lustre of their wings.

We didn’t see them go, but when we came back from a walk several hours later, they were gone without trace.

 The massing of Locusts happens in two stages. The first is of the immature stage, the flightless  ‘hoppers’ which emerge  in favourable conditions and gather in vast numbers. They look like small brown grasshoppers. We have seen great carpets of them moving across the ground, both in Greece and again in Australia. They will in time develop after more skin changes, into winged adult Locusts, and when these adults swarm in some years  they become one of the ‘Plagues of Egypt’.

Locust swarm in the air

Tree largely defoliated by locusts

We were initially puzzled when in Queensland we heard a subdued but insistent rustling and crackling. It was a vast swarm of locusts working their way through the savannah landscape of smallish trees growing in open grassland. They clustered in the trees till the branches drooped under the weight of the insects clotting every twig as they voraciously munched every leaf. You could hear them chewing and their frass (droppings) pattered down to the ground below where trains of ants were gathering it and carrying it back to their underground nests. The locusts’ wings rustled and shone silvery when the trees were stripped bare and they flew on, to land in the untouched trees ahead. They seemed to favour certain kinds of trees over others. Most sought after were Bauhinnias or Butterfly Tree.  A mob of Black Kites was swooping over them, picking off insects in their path.

 Sometimes you see the dispersal of these mass gatherings of creatures.  A few years ago, walking down the track from the Ridge Reserve in Luckett  Woods,  going steeply downhill towards the Tamar and the narrow flat strip with its damp drainage ditches alongside the river,  we met, toiling up  the steep hill, a crawling host of tiny toadlings, no bigger than the end of my thumb. There were literally tens of thousands all moving up and away from the river. They were not only on the track, but laboriously clambering up among the dead leaves and twiggy litter under the trees  alongside. We had to be careful where we put each foot as we moved downhill, against the tide. It was towards the end of our walk and I couldn’t face following them back up in the interests of science, to see how and where they started to fan out and scatter, as I suppose they would. I have wondered ever since!

We saw a similar happening of a carpet of toadlings spreading away from the shore of a shallow lake up in Gulf Country in northern Queensland. As ever, no camera!

Roosting beetles in the shade of a rocky overhang.

Some insects gather together in large numbers to aestivate, or roost in cool sheltered places to avoid the summer heat. We found the astonishing sight of probably thousands of a lovely iridescent  smallish beetle crowded together on the leaves of a plant growing in the damp shady underhang of the rocky cliff of a small gorge we were exploring in the Northern Territory.

Later on that same trip saw the aestivating roost of a great number of Australian Crow Butterflies  which were clinging to the leaves and twigs of a grove of small trees near a waterhole near Broome in the north of Western Australia. They were restless and easily disturbed This roosting isn’t true hibernation. 

Summer roost of Australian Crow Butterflies

Australian Crow butterfly

 An important cultural ceremony of one of the Indigenous tribes in New South Wales was based on the mass migration of a Moth. 

 

 The Bogong Moth of Australia.

Migrates in spring from further north and west to aestivate in close masses in the caves and rocky crevices of the Australian Alps in the southern part of the Great Dividing Range. The moths were particularly nutritious as they have thick fat-rich bodies and played a significant role in the people’s bush tucker.

Australian Alps where the Bogong moths  spend the Australian summer.

But the most famous of all these mass movements is the migration of the Monarch Butterfly from Canada and the northern States, to escape the cold winter and aestivate in the forests of Mexico, hanging in vast numbers from the trees. They return north the following spring, stopping to produce another generation partway on their journey.  In North America apparently the caterpillars feed exclusively on the Milkweed plant which grows further north and which gives this butterfly the alternative name of The Milkweed.

It is a handsome powerful butterfly and specimens can be found especially on the Cornish coast on occasions, presumable blown off course during their migration.  

Bristly Silkweed in Algarve, Portugal

 We have seen a small colony in The Algarve in southern Portugal where the caterpillars feed on the  Bristle-fruited Silkweed which is related to the Asclepias or Milkweeds , knows as such because of the copious milky sap exuding from the cut stems. It is a poison, and the Monarch butterfly carries this poison in its body, rendering it unpalatable to predators. 

Monarch caterpillar

And we found a caterpillar in New South Wales back in Oct ’89 but I forget what it was feeding on. ( I was told later it  would be on Silkweed). The butterfly, known for obvious reasons, as The Wanderer in Australia , has been known there since 1871. The Silkweed  plant is as big a wanderer as the Monarch. It originates in South Africa.

The Monarch Butterfly