Saturday, November 04, 2006

Itchy triggers

That bee-fly in the last post is quite a sizable animal. Big in fact. Probably about 20mm. This is one of the trigger plants that it would be fitted in size to pollinate, the Book Trigger Plant, Stylidium calcaratum.
This is an annual, up 20cm tall, with a long season from October to January. The common name refers to the fact that the flower closes like a book at night or in cold weather, obviously to save itself for when its specialist pollinators are out and about.
The flowers are white or shades of pink, and can be sprinkled as liberally as confetti around granite outcrops, edges of gravel roads and other water-gaining sites. The trigger is hinged so it strikes upwards, hitting the insect on the ventral rather than dorsal side. I wonder if that is more or less of a shock?

This is quite a widespread species, being found over most of the south west. It's also found in other states. WA has 70% of Stylidium taxa, so is a centre of Stylidium diversity, and the Busselton-Margaret River-Augusta region is particularly rich.

Rica Erickson's explanation of trigger plant action is still as good a way to read about them as ever.

Friday, November 03, 2006

Fly bee free

Bee flies and trigger plants. These are a few of my favourite things. Well, two. And there is a connection, happily.
This is a bee-fly - family Bombyliidae - and a true fly, not a bee. Interesting animals, bee-flies. Their larvae are parasitic on other larvae and eggs, often of Hymenoptera. The adults are nectivores, and pollinators par excellence. Their stout bodies are hairy and often dusted with pollen, just like native bees. They have hairless legs-and of course only two wings-so easy enough to spot from bees.
They also have a really distinctive flight pattern, hovering between bursts of incredibly rapid and buzzy horizontal flight.
And they are pollinators of trigger plants. Jan Taylor in his superbly illustrated book "Flower Power in the Bush and Garden" (not a title to inspire you to buy it but take my word for it, you'll love this book, especially if you're from WA. Out of print but keep your eyes open) explains that not many other insects visit Stylidium, "possibly because they are physically repelled by the trigger hitting them".
Indeedy. As you would be.
So our Bombyliidae are sturdy, intrepid little insects. Bless 'em. Not afraid of taking on the bullying triggers. And the size of Stylidium flower and the bee-fly that pollinates it are related. A bit of evolutionary flower power there.

But it gets even more interesting. The bee-fly is apparently no more keen on being knocked on the head by the trigger than any other insect, so it has evolved the habit of hovering over the flower, then landing upside down on the upper petals, thus not triggering the trigger.

Not to be outdone, the Stylidium has evolved all kinds of twisted and strangely angled petals. It can be very hard to tell which way is up. And not just for the bee-flies.

Jan Taylor, Kangaroo Press 1989;
Flower Power in the Bush and Garden, The Fascinating Interrelationships Between Insects and Plants.

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