Spilomyia sayi (Goot, 1964), not a wasp, just a good mimic |
Two syrphids of varying waspishness - both in looks and behaviour |
Flies have died from time to time, and birds have eaten them, but how about wasps? |
Blackjacket (Vespula consobrina) - a likely model for and predator on our local Spilomyia |
There was a study done back in the 1980s that looked at the phenology of wasps and bees, the mimics, and the fledged birds. As I recall, the recently fledged birds were more likely to encounter the models than the mimics, so that later in the season, the mimics would end up being confused with the Hymenoptera. I that the author was Waldbauer.
ReplyDeleteCould be, but here the wasps and mimics aren't common until the birds are fledging (I don't think any passerines raise broods after July here), so there's not much time to learn or hide. Also, at least when they are hanging out on composites in open areas, birds do not seem to be much of a threat. In the studies I've read (mostly with caged birds) the birds pounce from a perch. I suppose swallows may be doing some selecting in fields, but the other birds are hunting lower down. Wasps, spiders, ambush bugs, robber flies, etc seem to be the main predators of flies visiting composites in open areas.
DeleteI photographed what appears to be the same syrphid sp. (http://bugguide.net/node/view/695966)down in the river valley last Sunday. Its behavior was interesting too, as it was constantly flicking its wings as it roamed over the flowers. Could this behaviour perhaps be another way to deter patrolling hornets?
ReplyDeleteHi Adrian,
DeleteThe wing-flicking behaviour - a left-right waving of the wings - is interesting, but I'm not sure why they do it. I can't remember seeing any wasps doing it, so it doesn't seem to be mimicry. Maybe it's a "I'm bad, leave me alone' swagger.
The larvae of Spilomyia sayi occur in tree holes and rotting wood. I'm wondering if they like the birch bolts I spread around the garden after the drought? (Remember the drought - seems a long, wet time ago.)
Cheers,
Dave
Wow x 2.
ReplyDelete1st = that is a VERY impressive wasp mimic. Jeepers.
2nd = your catching it by hand = a VERY good time to have strong invert. ID skills. =)
I like your theory. I suspect trolling out the old " 'cause then birds won't want to eat it" chestnut is a reflex for many, and I suspect few of those who posit that theory (looked it up and "positer" is not a word, darn it!) know what you know about who actually eats those flies. I LOVE evolutionary/natural selection theory and the places it can take you.
A lot of 'mimics' seem very pro forma and one tends to wonder if their mimicry isn't more in the eyes of the (human) beholder than potential predator. But this is one of those multidimensional mimics that are beyond chance or cultural bias.
DeleteA little training, though, and the fly jumps out - only one pair of wings, too large eyes, wrong antennae. Telling a male from a female wasp is more difficult. Grabbing a male wasp to impress your audience is a better test of id skills (but I'm usually too chicken to try it when sober).
But I think the most rigorous test of taxonomic skills is eating wild mushrooms. If you are right, you have a good meal (at least with enough butter and garlic). If you are wrong, you may or may not have a good meal (allegedly deadly amanitas taste good), but you may live just long enough to regret your error.
I'm never sure what is a true wasp or not, and it looks like there is a good reason reading this post. Any guesses if this is a wasp or a look-alike of some kind?
ReplyDeletehttp://calgary-gardening-adventures.blogspot.ca/2012/09/wasp.html
Hi Middle Earth - looks like a look-alike to me.
ReplyDeleteI think you have a pair of mating Clearwing Moths (Family Sesiidae) - most of which mimic one wasp or another.
A good guess would be the American Hornet Moth aka Poplar Clearwing Borer, Poplar Crown Borer: Sesia tibialis (Harris, 1839). The larvae burrow through the cambium of aspen, poplar, green ash, lilac and other hardwoods.
Pretty cool mimic, because yellowjackets even mate that way - with the male dangling from the female (although male yellowjackets are more similar in size to females).
See: http://bugguide.net/node/view/160324
Also: http://www.entomology.museums.ualberta.ca/searching_species_details.php?fsn=Sesia&sb=1&r=2&o=1&c=2&s=6200&sn=Sesia+tibiale
NB - species name seems to be misspelled - tibialis in my books
Re the species name - 'tibiale' was Harris' original spelling (Trochilium tibiale Harris, 1839), but apparently his Latin should have been 'tibialis'. Some people follow the original orthography and some the ICZN suggested correction. An interesting piece of nomenclatorial anarchy!
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