100 More Species #22: Aphid killer

[urbpan]

Aphid killer, Tribe Syrphini

Alexis noticed this tiny caterpillar surrounded by aphids and ants on the underside of a nasturtium leaf. We deployed our excellent caterpillar guide, looking especially at the slug caterpillars, but came up empty. I looked for nasturtium in the list of caterpillar host plants, but only found the cabbage white, which this was not.

I decided to try bugguide.net, searching for caterpillar + aphids, figuring this relationship probably had been documented before. I found a post making the same wrong assumption we had: that this was a caterpillar. The assumption had been corrected: no dear fool, this is a fly larva. More precisely, it is the larva of a hover fly. Some hover flies start their lives as aphid killers, sluglike maggots that creep along plants gobbling up aphids as they go. There's yet another reason not to kill insects that resemble bees and wasps if you're not sure what they are. The bee-mimic hover fly you kill today won't produce any aphid killers tomorrow.

Astute readers will have realized by now that I have, yet again, cheated. This larva may very well be the same species as one of the adult hover flies I've already counted this year. Alas, there's no way to know, without collecting the aphid killer and rearing it to adulthood--these animals are not as well studied as many others, alas. But I thought the story and the creature were interesting enough that they belonged here, in spite of possibly repeating the same species.

Comments

[drhoz.livejournal.com]

neat :)

[badnoodles.livejournal.com]

It's an easy mistake to make, but I believe that only diptera have vertical, hook-shpaed mouthparts. And the posterior spiracles scream Brachycera. But that's me being all entomological.

I wish I had your photography skills - I have a new subfamily/tribe of Muscidae for BugGuide but I can't get good enough pictures to illustrate the diagnostic features.

[urbpan.livejournal.com]

Didn't even notice the mouthparts!

Thanks on the second point. Nothing worse than someone seeing a photo you're proud of and saying "Wow I wish I had a camera like that!" In this case, however, I think it might help you. My last few bugguide photos have been miles above, simply because I started using a different lens. Now I have a manual macro zoom on my digital slr. It's a little awkward (since the lens slides out when the camera is pointed down) but if I'm mindful I get much much better shots. What are you shooting with?

[badnoodles.livejournal.com]

I've actually got several options: There's a fixed-focus camera mounted into our laboratory microscope, which is a pretty crappy camera, but I can manually crank the focus down to get a series of montageable images.

The other is my new USB microscope, which gets decent magnification, but is very challenging to position and focus.

The last is my older DSLR that doesn't support interchangeable lenses. I do, however, have 1,2,4, and 10x stackable diopters, which do a decent-not-great job, and suffer from major depth of scale limitations.

[urbpan.livejournal.com]

Wow, I dunno. That sounds like pretty good equipment, but I'm not familiar with microscopy stuff. Mine were all from putting a hand-held camera on the lens. Good luck with it! Interested in being a guest on the podcast some time?

[badnoodles.livejournal.com]

Sure! I can talk about most insects competently, but disease-causing insects, filth-breeders, structure invaders, and anything to do with decomposition are my specialties.

[urbpan.livejournal.com]

AWESOME. I'm still technologically inept, so it may be some time before I can pull it together, but I'm dying to hear something other than my own voice on the podcast.

btw how's the job search?

[badnoodles.livejournal.com]

I remain thoroughly unemployed at this time. But I am taking my board certification exam in a couple of weeks, and attending the national forensic entomology meeting, so perhaps something will shake loose.

[urbpan.livejournal.com]

Excellent! Best of luck with the exam! Off to Vegas for the meeting?