I've been having great fun with my combination of extension tubes (70mm or so) plus my 50mm macro lens racked out to minimum focus. Total reproduction ratio is 2.4:1 on the sensor, meaning that the full frame covers about 10 x 6.5 mm.
Impressive figures, but what I love is that the photos that result give me something of the feeling I get from peering down a dissecting microscope. The minute beauty of nature's tiny creatures is apparent in a way that's well beyond the limits of the unassisted eye.
And so to the subject of this post, the emerald cuckoo wasp (family Chrysididae). I'm sure that most people don't realise how common these are. I'll bet they'd turn a few more heads if they were over five millimetres in length. If you want to see some for yourself, just keep your eyes on a brick wall (corners seem to be preferred) in the sun on a warm day.
What they're after are the nests of other wasps. Things like mud-dauber wasps I'll bet, though I've never actually seen one have any success in its search. Like the cuckoo bees that I've written about in the past, these wasps are kleptoparasites, laying their eggs in the nests of other wasps whereupon the larvae eat the provisions and/or the host's larva.
Have a look at chrysis.net for more information and some great pics of cuckoo wasps from all over the world. There's a great part of the story that I gleamed from that page. After the cuckoo wasp makes a hole in the mud structure of its host, it lays its egg inside, then seals the hole back up! Apparently this is to stop mould getting in and wreaking havoc.
And of course, the metallic iridescence that characterises most of the group is another example of structural colour, rather than pigmental.