Thursday, June 21, 2007

A Hoverfly, Syrphus ribesii

I am an amateur trying to learn a little about every creature in my garden.

I recently blogged the blooming of the California poppies in my garden, and it was on one such flower that I found the hoverfly seen in photo 1 (click to enlarge).

For the amateur naturalist attempting to decide which of the 250 British (or worse, several thousand global) species of hoverfly you are looking at, an obvious first problem is how do you know you're looking at a hovefly at all, as opposed to any of the much larger class of non-hoverfly flies? The answer is easily stated, though perhaps not so easily observed in the wild: hoverflies (family Syrphidae) are distinguished amongst the flies (order Diptera) by the presence of a vein that runs along the edge of the wing together with a so-called 'false vein' running along the wing's length. Houseflies, for example, have neither. I don't have access to fancy photographic software, but in photo 2 I've done my best in to enlarge and highlight these features for the hoverfly in the photo above.

The above facts, and just about everything else I've learnt about hoverflies I've garnered from the excellent Hoverflies (Francis S. Gilbert, publ. Richmond, 1993). This book, written for the amateur naturalist, contains a wealth of detailed but easily digested information. It also contains some beautiful colour plates, by which I believe I've identified my hoverfly as Syrphus ribesii (I haven't found a common name. Anyone?).

Hoverfly adults visit flowers to feed on nectar and pollen, the latter as it contains necessary carbohydrate (typically about 25%; nectar has none). It's believed that hoverflies select flowers mostly on colour (rather than e.g. scent). Yellow seems a particular favourite. Whilst the adults may be peaceful vegetarians, the larvae of S. ribesii are aphid predators.

One of the impressive abilities of S. ribesii is its ability to regulate it's body temperature somewhat by vigorously 'flapping' its wings whilst remaining perched. On cold mornings, the 'whine' of S. ribesii males can be heard in woodland as they seek to build up body heat, driven by the urge to get airbourne and seek females. It is apparently even possible to hear the pitch increase as their body temperature rises- like a jet engine powering up - something I'm determined to listen out for.

A particularly inspiring feature of the book above is that the author tabulates a whole series of unanswered hoverfly puzzles of genuine scientific interest to the professionals, yet simultaneouly fully amenable to study by the amateur: "Do predators such as wasps take feeding hoverflies. How risky is feeding is feeding at different flowers?"; ""Is there a definite [hoverfly] courtship? What is it like? How long does it last?"and a dozen others. I personally find it inspiring to know that even in the household garden there is a complexity that exceeds our current best understanding, and yet may require no more than patient observation to unlock its secrets.

Horray for the humble hoverfly!

8 comments:

R2K said...

Hey I have started a new microscope project to create images of larger scale objects by taking a set of small Proscope images and putting them into a mosaic. So far my results have been mixed, but with more practice I expect to get better. Please feel free to view my first post on the subject. You can see that some images work well and others do not.

Keri Dearborn said...

Henry, We are doing similar observations on almost the opposite side of the world. How exciting to find a fellow fan of hover flies. I must say your California poppies look lovely. I have only occasional success with them. Your photos are wonderful. Only 26 species? I'm sure you will find more. I'll keep checking back to see what you find.

Muppet said...

Hello!

I have nominated you for a 'Bloggers for Positive Global Change'.

Check out my post at http://tinyurl.com/ytpfrp for more details :o)

Emma

R2K said...
This comment has been removed by the author.
R2K said...

I cant wait to see more!

Henry Walloon said...

Keri, Muppet and R2K - many thanks for the kind comments here. After some delay I'm back!

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