More confusing flies

There are masses of these insects about the place at the moment, as our unseasonally warm weather continues to encourage all the invertebrates to swarm about like it's February already. I fantasise that I live in Cairns and can almost see lightning cracking over canefields.

But I digress - at first glance I thought this was a tiny wasp, (it's appearing in sizes from tiny to small - 5-10 mm versions) it has all the right waspy colours and a nice wasp waist. Then a closer look made me see just two wings so I thought bee-fly. Then a very close look made me think
hoverfly.




Hoverflies do the Batesian mimic thing very well, deterring predators by having that bee or wasp lookalike demeanour. Looking at a close-up of this flies wings, it's striking that the veins don't go all the way to the wing margin. This is characteristic of hoverflies, creating what is referred to as a "false margin". The other noticeable thing about this fly's wings is the scale over the halteres - a squama.
Here's a pic of a bee fly wing to emphasize the difference. This is the one from a week or so ago. It's a spectacular wing venation - just look at those lovely scrolls.



And here's a classic hoverfly wing - this is the introduced drone fly, Eriastalis tenax, the rat tailed maggot fly.



And here is today's fly. I'm not sure it's a hoverfly, so the mystery is still out there for the solving.

Charming!

Just because it's trigger season, and I live in Stylidium central, here's one of my favourites that is flowering now. The Lovely Trigger Plant, Stylidium amoenum (amoenus is Latin for charming or showy). In a genus of exquisite plants, you have to be special to earn a specific epithet like that.
(It appears to have been collected by Robert Brown, botanist on Mathew Flinders voyage. I think he had more than a passing acquaintance with curious and attractive flowers, but in those days Stylidium were classified as Lobeliaceae, though Brown had his doubts).

It is happily abundant in Jarrah forest over quite a large area of the S.W., but seems sadly to be a Phytophthora cinnamomi martyr. Grows up to half a metre tall, and flowers for a long period from late spring.

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.

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.

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