Tachinid Fly ID?

col188 · #1 (**permalink**) 14-06-2009, 11:09 PM

Anyone help with ID of this Tachinid fly, caught in the act of egg laying. Nearest i can discover is Sturmia bella. But then I know nought and there are quite a few.

col188 · #2 (**permalink**) 15-06-2009, 07:20 PM

Must be very rare......

Jason Green · #3 (**permalink**) 15-06-2009, 07:35 PM

Hi Colin,

I'm pretty sure your fly is not S. bella, due to the conal abdomen - though I agree in other areas it looks similar. This fly I photographed back in 2008 has been given the 'It looks good for Sturmia bella as far as you can tell in a photo' kind-of-way, but it's often a disection job for the sake of 100% certainty...

Sturmia bella arrived in the UK in Hampshire in 1999 perhaps as the result of butterfly caterpillars being imported for wedding releases - the caterpillar is parasitised in the country of origin, the out pops the fly in the UK! It has affected the numbers of the Small Tortoiseshell, which for other reasons as well has gone down by 80% in some areas. There is no real idea of it's UK distribution, though suffice to say it's recorded in London and other parts of the South-east.

I hope this helps.

col188 · #4 (**permalink**) 15-06-2009, 11:14 PM

Quote:

Originally Posted by Jason Green

Hi Colin,

I'm pretty sure your fly is not S. bella, due to the conal abdomen - though I agree in other areas it looks similar. This fly I photographed back in 2008 has been given the 'It looks good for Sturmia bella as far as you can tell in a photo' kind-of-way, but it's often a disection job for the sake of 100% certainty...

Sturmia bella arrived in the UK in Hampshire in 1999 perhaps as the result of butterfly caterpillars being imported for wedding releases - the caterpillar is parasitised in the country of origin, the out pops the fly in the UK! It has affected the numbers of the Small Tortoiseshell, which for other reasons as well has gone down by 80% in some areas. There is no real idea of it's UK distribution, though suffice to say it's recorded in London and other parts of the South-east.

I hope this helps.

Thanks Jason,
Had a good search of the Photos at Tachinidae.org but couldn't spot it. Apparently dissection and a microscope's not foolproof either.

Col

ChrisR · #5 (**permalink**) 02-10-2009, 10:13 AM

Sorry - catching up so this is a bit of an old thread ...

It's certainly a tachinid but I can't really think what it might be - perhaps Exoristini?

The photo of Sturmia bella certainly looks as convincing as you can get without actually seeing a bristle-comb on the hind tibia

They are pretty easy to identify but it's just a problem to see the necessary bits because they are often hidden in photos. Dissection isn't necessary for most tachinid identifications but you do usually need a dead specimen and a decent microscope and keys.

Sturmia has, in my opinion, been unfairly blamed for the decline of the Small Tortoishell. Owen Lewis has been working on a project to work out what effect Sturmia has had on the ST population and his first year's results basically couldn't find any statistical difference between the decline in areas with Sturmia and those without Sturmia. Also, ST was declining from the early 1990s but Sturmia (a large, distinctive fly feeding on commonly reared hosts) was only recorded first in 1998. Furthermore, in mainland Europe it is a common, native fly and they have had no problems with decline in vanessids ... and in counties like Dorset, with good habitat, and Sturmia populations ST seems fairly common.

My own personal opinion is that ST has suffered badly from human damage to its favourite habitats (loss of nectar plants and foodplants etc) and the environment (global warming changing the phenology of various species). Common-ness (is that a word?!) is not always a good indicator of an ability to resist pressures and there is likely to be a number of factors that have caused the massive decline seen in large areas of the UK. If Sturmia has had any effect at all then it will have just been a final-straw in some parts of the country, depleting an already vulnerable species teetering on a tipping point.

As another example, the Wall Brown was once a very common species in Oxfordshire - when I was a kid in the early 1980s you couldn't fail to see it on any trip to the Ridgeway. Then sometime in the early/mid 1980s the population collapsed and it is now found mainly in coastal counties ... I am not sure what caused the collapse but I don't think anyone has suggested that it was the result of a parasitoid

Chris R.

col188 · #6 (**permalink**) 02-10-2009, 11:40 AM

Thanks Chris........ Unfortunately (for id purposes) I don't take specimens, more interested in the photography aspect.

Matching up to book or on-line images images/drawings etc is very difficult though
Col

ChrisR · #7 (**permalink**) 02-10-2009, 11:48 AM

Quote:

Originally Posted by col188

Matching up to book or on-line images images/drawings etc is very difficult though

Yes, difficult and very unreliable but it's good enough for a personal 'tag' to put on your photos.

One of the problems is that some features that your eye is draw to on photos are not reliable - such as body colour or dusting or even wing venation sometimes. Keys take the user through layers of tests on features like hairs and bristles that are not infallible but are quite reliable and do at least take into account all the possible species (including rarities). The best thing you can do with a tricky photo like this is to post it on http://diptera.info/ and see if someone better than me can identify it