Biological phenomenon!

We went to Evie beach on Wednesday (02/02/2022) good decision. An extraordinary spectacle met us, billions, maybe trillions of flies emerging on and around the beach. There were a number of species involved, but the kelp fly Coelopa frigida was the most obvious.

It was hard to photgraph them and give the sense of numbers. We could easily hear them as we walked along, the flapping 2x trillions of wings. It was like rain hitting our clothing, we keep our mouths closed tight!

Huge numbers of birds were feeding on them.

And looking closely on the shore pupal cases and, under turned stones, many larvae.

Pupae above, larvae below, probably of Coelopa frigida.

A look closer.

The close up shoes the bare side to the thorax which thus keys to the species pair C. frigida and C pilipes, technically, "anepisternum bare or with short bristles only towards the lower rear part. I identified these as frigida due to the lack of setae on the ventral surface of the subcosta of the wing. But I think, C. pilipes, which I've not seen, is covered in fine hairs all over its legs, so it looks kind of shaggy.

I didn't take specimens of the smaller Dips, probably a mistake, but I'm trying not to overwhelm myself at the moment. Louise did catch a large Dip which I brought home, and am still trying to figure out. There were a few of these about, on the car and on track puddles.

This can't be C. pilipes as the anepisternum is hairy and has strong setae, but I'm struggling with the Unwin key at the moment. It is Scathophaga calida, which is not all that common so good result, thanks TI.

Amongst the birds was a nice 2cy Iceland Gull.

Iceland Gull, 2cy.

There were plenty of the commoner gulls and lots of small waders as well as 100s of Starlings, Rooks and Jackdaws. 

About 300 Turnstone and 200 Purps as well as Redshank, Dunlin, Ringed Plover, Sanderling.

Even the Snow Buntings joined in descending onto the kelp to feed at one point.

Snow Buntings.

Also washed up with the tons of kelp were the bryazoans Square-ended Hornwrack and Sea Mat. I found the egg case of dogfish and Flapper Skate.

Dipturius intermedius, Flapper Skate, egg case.

Sea Mat, Membranipora membranacea, a bryozoan, on kelp.

Small Spotted Cat-shark, Scyliorhinus canicula, egg case.

Square-ended Hornwrack, Securiflustra securifrons, a bryazoan.

The worm, Spirorbis spirorbis, on kelp.

I was a bit disappointed that the hornwrack sample I took was the less common (?) Square-ended as I haven't previously recorded the common HornWrack and I bet it was there amongst the kelp.

Before we left, a check on the car park beach found quite a few of this common shoreline Collembola, which by a bit of luck, especially as it was 2mm long, I managed to get a half decent image of.

Anurida maritima.

An extraordinary spectacle which, I've now learned, was repeated on a number of beaches and islands across the county. It would be interesting to pull together where on Orkney this did and did not occur, if it occurred south of Orkney or in Shetland on the same day. I'm guessing the trigger was the huge quantity of kelp deposited on the beaches recently and the relatively calm, warmish (certainly ish) day.