Sunday, 3 July 2011

School Trips

This is the time of year when I take school groups out on walks to show them the delights of our countryside. I'm normally too busy doing identifications to get decent photographs, but I do manage to squeeze in a few.

This is the major season for hoverflies: hedgerows, verges, gardens and woodland are all buzzing with them as they carry out their vital pollination.

This is Cheilosia illustrata, which I only ever find - in small numbers - on Umbellifers (Hogweed in this instance) at the edge of woodland:
The hoverfly Cheilosia illustrata
The larvae of Cheilosia illustrata mine the lower stems of Hogweed.

The Syrphus family hoverflies are all very similar and can usually only be separated by examining microscopic characters.  This is Syrphus torvus, which can be identified by the hairy eyes:
The hoverfly Syrphus torvus (male)

The larvae of Syrphus torvus are aphid eaters.

New to me.

One of the great things about the internet is the way in which it connects people. As a result of online communications, I know that there has been a recent inwards migration of numerous butterflies, moths and other insects; Eupeodes corollae is one of them:

The hoverfly Eupeodes corollae
The larvae of Eupeodes corollae are also aphid eaters.

Soldier Flies are often mistaken for hoverflies, but the wing veins are distinctly different. There are a few metallic hoverflies, so the confusion is understandable.
Soldier Fly - Chloromyia formosa

This is a suitable place to show an Ectemnius wasp. Ectemnius wasps make solitary burrows for their larvae, which they feed exclusively on hoverflies. They have evolved to resemble hoverflies, presumably so that they can sneak up on them without causing them to fly off.
Ectemnius sp. wasp

Sometimes an opportunity arises to take a photograph which definitely fits more into the 'artistic' category: 

This Ichneumonid was closely examining the flowers of Bush Vetch in the hope of finding some larvae to parasitise. I saw this backlit shot as it was moving from flower to flower:
Ichneumonid on Bush Vetch
And now my new favourite photograph:

Ichneumonid parasitising moth larva in Cocksfoot grass
The female Ichneumonid has detected a moth larva inside the seedhead of Cocksfoot grass, and has swung her ovipositor round to inject an egg into the caterpillar. The egg will stay dormant inside the caterpillar until it pupates, at which time the egg will hatch and consume the contents of the cocoon. It takes a great deal of patience to get a shot like that. Each shot requires perhaps 30 minutes of watching the wasp moving from seedhead to seedhead and waiting for the moment of injection. These are my favourite photographs.

This has been a tricky year for Damselflies and Dragonflies: I have seen very few. A trip to a local pond solved that for me. This is The Blue-tailed Damselfly:

Blue-tailed Damselfly

And this is the Variable Damselfly - Coenagrion pulchellum, which is new to me:
Variable Damselfly

A tall, elegant grass has been bothering me for a couple of years, so I decided to identify it this year. It's Tufted Hair Grass - Deschampsia cespitosa - which forms tufts and has stems that reach up to my shoulders. I usually find it where I would normally see Damselflies, so they must need similar conditions.

Tufted Hair-grass Deschampsia cespitosa
New to me.


Emma Springfield said...

You are amazing with your identifications. The two damselflies look almost the same to me as do the various flies.

Gill said...

I love that shot of the little ich on the bush vetch. Interesting that you're getting lots of hoverflies - so far here in Yorkshire there are fewer than usual.

I'm intrigued the Deschampsia is new to you - it's one of my commonest grasses - I was walking through a whole field of it yesterday - lovely mauve 'sea' though here it is usually waist- rather than shoulder-high.. Just watch the leaves which can cause a very nasty cut, especially if you ill-advisedly try rubbing your hand down them. Vicious!

Stuart said...

Emma: identifications can be extremely tricky, whether it's plants, fungi or insects. When I show a picture, it doesn't mean that the specimen shown can necessarily be identified from that particular shot: critical features might be hidden or too small to see. I take a lot of shots that aren't shown and I often have to resort to microscopic analysis to confirm identifications. The bad news is that as a generalist I must maintain a huge library of expensive references. The good news is that many species - once they have been through the initial investigative process - can be readily identified by their behaviour or 'jizz'.

Gill: the grass isn't new to me, but its name is: I think grasses can be quite difficult, and it takes a mighty resolution for me to sit down with a specimen and the books.

Rob said...

Fantastic shot of the ichneumonid - patience rewarded!

Stuart said...

Rob: Ichneumonids fascinate me, and I could happily research them full-time. We have perhaps 6000 species, but the documentation is scarce and fragmented. You need to get these under a microscope to accurately identify them, since the 6000 or so species converge on very few colour patterns. To give an idea of the complexity, the key to subfamily of just one family of ichneumonids - Braconidae - runs to some 120 pages.

The next post has another shot of the one laying into Cocksfoot grass, showing the instant of deployment of the ovipositor. I noticed over the past few days that this laying has stopped, so we have perhaps 3-4 days per year when this particular specimen can be seen and photographed. That's very tight synchronisation.