Strange protrusions on hoverfly larva

[Bruce Williams]

The pic is of the head (or maybe tail) of an unidentified hoverfly larva.

I say 'strange protrusion' because their function is not immediately or intuitively obvious (at least not to me anyway). So, anyone know what the two knobbly things are? I have seen very similar on other species of hoverfly larva.



See also from an earlier posting of mine:



Bruce

[loripo]

I was looking at your first post on these. I got a photo of a transparent pupa a few days ago where you could see the hoverfly inside. I came across this...
Syrphid larva devouring aphids 5-13-08 - Syrphus - BugGuide.Net

Do have a look at the second half of the video mentioned.

[Bruce Williams]

Thanks for posting that link Lori - The pics were helpful and the video was interesting too - at least I now know which end is the head .

I've ordered a book on identifying hoverfly larva and I'm hoping there will be some basic info on anatomy.

Bruce

[Rossco]

Bruce, the protrusions are the larva's spiracles - the structures it breathes through. Most fly larva have evolved spiracles just at the hind end rather than on each segment because they spend most of their time head down in some manner of filth. Hoverfly's have obviously retained this set-up.

In many species, the spiracles are very important in identification.

Good anatomical photo by the way.

Ross

[Bruce Williams]

That's really helpful Ross and much appreciated.

Bruce

[loripo]

Originally Posted by Rossco

they spend most of their time head down in some manner of filth.

I'm sorry - this is an interesting answer but that comment made me laugh. I feel like life does that to me some days

[Rossco]

Originally Posted by loripo

I'm sorry - this is an interesting answer but that comment made me laugh. I feel like life does that to me some days

Don't we all.

[Bruce Williams]

In this morning's post I received a copy of the "Colour Guide to Hoverfly Larvae" by Graham E. Rotheray . It contains quite a few anatomical diagrams and says this about the "strange protrusions (referring to a diagram)":

"At first sight it might be difficult to see anything that could possibly work as a recognition feature i.e. a feature that all uniquely possess, the presence of which identifies them as belonging to the family Syrphidae. Fortunately, however, there is just such a character - the posterior breathing tubes. In hoverflies these two tubes are fused at the point they emerge from the body into a single, elongated, brown or black structure. ............Note, however, that the breathing tubes of first and second stages of all homopteran predators (.....) are separate, so be cautious in identifying all such larvae less than 6mm long.". Apparently all hoverfly larvae pass through three instars (bw).

The book also refers to the posterior breathing tubes as the "posterior respiratory process (prp)". As Ross said, the prp carries the posterior spiracles and can be an important factor in identification.

Bruce