Black soldier flies are not vectors of human pathogens

Can I guarantee that you won’t get sick from contact with black soldier flies?

There is no species of animal on Earth that could live up to that guarantee, but researchers agree that black soldier flies (Hermetia illucens) are not disease carrying pests like common filth flies.

handful of black soldier fly larvae

Black soldier flies are different

I can understand people’s revulsion at the thought of flies in general. The common house fly is associated with 277 disease organisms. On the other hand, BSF have been the subject of many scientific studies and they are not known to be transmitters of disease causing pathogens. I’ve read dozens of articles about using the larvae to process manure and about feeding them to animals and I’ve never come across any warnings about handling BSF. It’s easier to find information about humans transmitting pathogens than about BSF doing so. You can, however, find some nice photos of researchers holding big handfuls of BSF larvae and smiling broadly (the researchers that is). There are several aspects of the BSF life cycle that result in their non-pest status.

black soldier fly blog logo

All flies emerge relatively clean

The process of pupation results in all flies emerging relatively free of pathogens. It’s the lifestyle of the adult flies after that point that makes the difference.

BSF adults (winged stage) only live for a few days as opposed to 30 or more days for house flies. Because of their short lifespan adult BSF don’t need to eat and in fact don’t even have working mouth parts. For that reason they rarely enter human habitats and they don’t compete with humans for food. House flies must eat so they cycle back and forth between waste material and our food. It’s that cycle that results in the transfer of pathogens and it’s the absence of that behavior that keeps BSF relatively clean.

After emerging, the adult BSF mate and the female flies away in search of a suitable food source to lay her eggs near. The female’s preferred site for depositing her eggs is close to, but not on the food source. Eggs laid on the food source will have a high chance of being inadvertently consumed by already feeding larvae. This is another characteristic that contributes to the BSF status as a non-pest species.

Unlike many other flies, BSF adults do not go into houses, they do not have functional mouth parts, they do not eat waste, they do not come into contact with waste, they do not regurgitate on human food, and consequently, they are not associated in any way with the transmission of disease. They do not bite, bother or pester humans in any way. - Dr. Paul Olivier


The amazing digestive system of BSF larvae

In contrast to spreading disease there is evidence that the presence of BSF larvae can reduce pathogens in waste material.

Bacteriological interactions associated with manure digestion by maggots are favorable. Maggots are competitors with bacteria for nutrients and often reduce bacterial numbers greatly, or eliminated them altogether (Beard and Sands, 1973; Sherman, 2000). Maggots may consume and digest microorganisms, and produce antibacterial and/or fungicidal compounds (Landi, 1960; Hoffmann and Hetru, 1992; Levashina et al., 1995 and Landon et al., 1997). As maggots reduce pathogens in manure they may make it safer for organic vegetable production.

From the same article:

Flies that have been used experimentally to process manure include house flies (Musca domestica), face flies (Musca autumnalis), blow flies (usually Sarcophaga sp.) and the black soldier fly (Hermetia illucens). Except for the black soldier fly (Furman et al. 1959), all of these are considered pests as adults due to their disease vector potential, behavior and preferred habitats.

Preliminary studies with black soldier fly larvae indicated a reduction of pathogens in an artificial medium or manure innoculated with larvae. Numerous studies using dried, rendered and fresh maggots as animal feed have revealed no health problems resulting from this practice. Preliminary bacterial culturing of self-collected soldier fly prepupae from a recent swine trial revealed no pathogens


BSF larvae lessen or eliminate the breeding of pest flies

When a food source has an established colony of BSF larvae other species of flies are rare or even absent. The larvae produce an info-chemical that alerts other flies to the fact that the source of food is already being dominated by BSF larvae.

Common sense about working with black soldier fly larvae

I’m not suggesting that black soldier flies or their larvae are perfectly sterile. You and I are not perfectly sterile. Pathogens are everywhere and it is common sense to wash your hands after working with BSF, just as you would after petting a dog or shopping at the grocery store.

Comments 12

  1. Mosey wrote:

    Very interesting article here! :) I haven’t yet read the source material so will still need to look them up, but have to say the larvae look more like woodlice in your picture!

    Posted 19 Jun 2008 at 9:26 pm
  2. Jerry wrote:

    Hi Mosey, thanks for visiting! The BSF larvae do resemble woodlice in a photo, only the BSF are MUCH prettier. :)

    Posted 20 Jun 2008 at 7:14 am
  3. Dirk wrote:

    I found BSFL in my compost last year and looked them up online and the info I found on them made me happy. They are impressive little critters.
    So far this year they haven’t made an appearance in my compost. I think it’s because I haven’t been stopping by the coffee shop and getting grounds like I did last year. It seems they really like that stuff.
    Glad to see your blog. I think these critters are awesome.

    Posted 25 Jun 2008 at 2:15 pm
  4. Jerry wrote:

    Hi Dirk.

    I’ve noticed the same thing about BSF and coffee grounds. Could they be caffeine junkies? One theory I have is that the grounds help them digest food more efficiently because of the caffeine, the texture, or both.

    I’m glad you found my blog and I hope you’ll let us know if any BSF larvae show up in your compost.

    Posted 25 Jun 2008 at 8:52 pm
  5. Brian wrote:

    BSF larva are also known as ‘Phoenix Worms’ and are excellent feed for insectivores such as Reptiles, Birds, Tropical Fish, and Sugar Gliders. They are High in calcium (about 50x +/- more then other feeder insects) and lower in fat. They also make extraordinary composter insects that can consume large quantities of food including meat and dairy before it even rots.

    Posted 20 Aug 2008 at 11:22 pm
  6. simone wrote:

    I’m in Maryland. Had to go to metal trash can composters, as there is a rat problem here. Noticed maggots in the compost this summer. But how do I know whether they are the disease carrying houseflies or black soldier flies? Thanks.

    Posted 27 Sep 2008 at 10:27 am
  7. Jerry wrote:

    Hi simone,

    House fly maggots are smaller than that of black soldier flies. A BSF larvae can reach almost an inch in length.

    You can also observe the area where the maggots are located to see what type of fly is present. If you see more than 3 or 4 house flies around the pile then the larvae are probably not BSF. If you see no, or few houseflies around the pile I would suspect you have a BSF colony because BSF larvae give off an info-chemical that repels other species of flies.

    If you really want to be certain about the species the best way is to put a few maggots in a jar and see what develops. If you provide them with food, water, and air you will soon have an adult fly to identify. House flies develop much quicker than BSF so if you have them you’ll know within a few days.

    Posted 27 Sep 2008 at 2:21 pm
  8. Jarrett Arnold wrote:

    Me and my daughter found tons of these bad boys when stirring the compost today, we immediately recognized them as larvae, thought fly species likely, and found our way to here from searching “big larvae in compost” then searching the genus and species viola! Not many flies found in compost have such large larvae- a handy characteristic for identification. They actually look much less dingy when you bathe one in water. less brown, more yellow. We especially like their pointy heads (my son, daughter, and I) This blog is excellent, we’re going to slap the one we bathed under the dissecting scope to get a closer look. I can email my drawings if they’re any good and you are interested. I am a lab instructor for an ecology class at the University of Oregon. Me and my children study insects for fun. Thanks for a great blog, good info can be hard to find.

    Posted 29 Sep 2008 at 10:10 pm
  9. Jerry wrote:

    Jarrett, thanks for the kind words, I’m glad you had a good experience with the BSF larvae. I was laughing at myself today because I was cleaning up on of the three larvae I’ve been photographing daily. You can see that thread here. One of them had a piece of food that didn’t wash off and I had a tissue rolled up and I was gently wiping it clean.

    I would love to see the results of your examination.


    Posted 29 Sep 2008 at 11:12 pm
  10. Pego wrote:

    Zoonotic Parasites?

    Like many pet owners I have a pet poop problem my BSFs LUUUUUV poop and have taken over the bin I used to deposit them in. The resulting compost I have dropped on the landscaping trees and not much else because I’m conserned about the possibility of zoonotic parasites.

    Has anyone studied this as a transmission vector?

    Posted 09 Dec 2008 at 1:35 am
  11. Jerry wrote:

    Hi Pego, sorry it took me so long to respond!

    I don’t believe there is reason to worry about using the compost for growing vegetables. I’ll check back when I have some sources to share.



    Posted 15 Dec 2008 at 8:49 pm
  12. Pego wrote:

    I am very interested. I am ina pet service industry and find myself giving the Toxocariasis lecture to people who hqave the perfectly normal idea of walking barefoot in the grass that has had pet traffic. I would so love to see some research and show it to some of my clients and friends.

    Posted 16 Dec 2008 at 2:42 am

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