Wednesday, 13 April 2011

Early year?

I'm hearing many reports of species being 'early' this year. Species have been appearing at earlier and earlier dates over the past few years; so much so that it has almost become the accepted norm and people don't even mention it any more. But this year I'm again noticing that more people are making special mention of early specimens of moths, butterflies and other insects, so perhaps things are particularly early this year.

The following shot certainly illustrates that trend as far as I'm concerned, but before I discuss it, what type of insect do you think the following picture shows? (bumblebee, wasp, fly, other?):


Male Eristalis intricarius
Well, to put you out of your misery, it's a hoverfly: a male Eristalis intricarius. These are good bumblebee mimics, and at first glance, when they're stationary, they are easily mistaken for Bombus lucorum.

A few identification pointers might help. Firstly, it has only two wings; flies have two wings, bees have four. Secondly, the head is almost completely made up of eyes. In a bee, the eyes are long and narrow, with visible parts of the 'face' on both sides of the eyes. (Incidentally, the fact that the eyes meet in the middle is what makes it so clearly a male). Thirdly, what appears to be an orange stripe between the wings is actually the shiny scutellum, and isn't really a stripe at all. Finally, if you look carefully at the wing veins, you can clearly see the famous 'Eristalis bulge', which is unique to the Eristalis group of hoverflies:

Eristalis 'bulge'
The shot also illustrates another of the wing features which identify hoverflies: the 'False margin':


The trailing edge of the wing is not constrained by a vein: it is free to flex as the wing moves. I rather suspect this is one of the main reasons why a hoverfly can hover so accurately.

In terms of earliness, I have only once seen Eristalis intricarius before June: I have come to regard it as a summer species. The references say from March, but that would probably be a date from much further south.

The next shot shows a couple of tiny flies (on Dandelion for scale). On the left is a Sepsid fly: these run around on leaves and flowers with their wings flapping up and down in a semaphore fashion. On the right is one of our smallest hoverflies, Neoascia podagrica:

Sepsid (L) and Neoascia podagrica (R)

Here's a close-up of the (8mm. long, female) hoverfly:


This is again much earlier than I would normally expect to see it.

In terms of grasses, the first to flower around here is usually Sweet Vernal Grass, but that hasn't appeared yet.  Instead, I found Meadow Foxtail:

Meadow Foxtail
I have included a little insert (top left) showing the very short 'ligule' which can be used to assist with identification.

6 comments:

Colin Griffiths said...

I really am enjoying your blog and I learn something new and enriching with every post you make. Thank you!

Stuart said...

Colin, thanks for that. I'd good to know that people benefit from something that I enjoy.

Gerry Snape said...

Stuart,
I just love this blog it helps me inform my grand daughters. That was so interesting about the hoverfly as I immediately thought that it was a bee. So we shall be more thorough in the future in our back field with the many flies etc. Yes I too think that things are early here in the N.W. of England

The Weaver of Grass said...

Our blackthorn is better this year than the farmer can ever remember it and he was born in 1943! Also the first swallow appeared on April 6th - the earliest before was 9th - we record the date each year.

Stuart said...

Gerry, I'm glad it's helping you to bring wildlife to your grand daughters. My interest in wildlife was started by an uncle who took me out into the wilds as soon as I could walk. In terms of bees vs. hoverflies, their flight is very different, and the landings even more so. Bumblebees tend to crash into flowers whereas the hoverflies land very gracefully.

Weaver, yes.....Blackthorn is showing particularly well this year. It's only when it's flowering that I realise just how much of it there is around us. It's pretty anonymous later in the year.

Caroline Gill said...

A truly fascinating post, Stuart. Those Photoshop arrows are a huge help, too. I certainly would have guessed 'bee' rather than 'hover fly' ... how wrong we can be!