BSF larvae or housefly maggots?

[Beekeeper]

Hello,

I'm just getting involved with BSFL, and have been trying to attract egg-laying females to a 5-gallon bucket full of table scraps.  I checked this morning and have found a bunch of some kind of larvae, maybe black soldier fly, but maybe housefly maggots -  I just don't have enough experience with either one to know the difference.

I haven't seen a housefly around here for some weeks, but I did see a BSF around the bucket a few weeks ago, so I am hopeful.  I live in climate zone 9-10, so it seems possible that the organisms are BSFL.

Is there a good way to distinguish between housefly larvae and BSFL?

Thanks,

Mark McClure
Santa Barbara, California

[GW]

Mark, there are a few simple ways to tell them apart.

Size - Housefly larvae reach a length of approx. 12mm and BSF larvae grow to 19mm (3/4 inches) or more. BSF larvae are much thicker than housefly larvae.

Appearance - Housefly larvae are smooth and BSF larvae have distinct ridges.

Development - If you're regularly observing the waste material and larvae you might get clues there. Housefly larvae mature in as little as 4 days under ideal conditions and BSF take a few weeks. Housefly eggs hatch in about a day and BSF eggs require 4.

Aariq uploaded a great photo of BSF larvae from his central Illinois compost pile that shows various sizes and stages of BSF larvae:



In this photo you can see the range of colors for BSF and the ridges are also clear. I believe housefly larvae are usually lighter in color and they are obviously smoother.

Hope that helps!

[Andrew]

I'm pretty sure the smoother, lighter ones are housefly larvae. The ridges of the BSFL are much more prominent - very armor like.

[GW]

Andrew, if those non-BSF larvae are as large as they seem to be then I don't think they're housefly larvae. Blowfly larvae do get that large I believe. A good way to tell what they are is to allow them to pupate and emerge in a container.

[Andrew]

Jerry, I should have put something in there for size reference. The BSFL were younger juveniles. The largest one was maybe 1/2"? The largest pale larvae was about as big as they got. I didn't think to see what hatched out. I just smashed them all.   

The other larvae appeared when I put my bin outside, so you're probably right and they were blow fly larvae. The photos on the 'net also don't show size, so I just went by appearances and the house fly larvae pics I saw seemed close enough. I think I did read somewhere that housefly larvae did get to be 1/2" in size.

[GW]

I'm traveling now but when I get home I'll post a photo of a BSF larva next to another large fly larva I found in a garbage can. They are about the same size at around 3/4 inches (19mm) and a similar shape. I kept the other larva until it emerged as an adult and it appeared to be a False Stable Fly. I'm not a big fan of the disease carrying fly species but I must admit that this was a handsome insect.