First, no, BSF adults cannot harm your house or you. BSF adults (winged stage) do not eat as their only purpose in the few days they live as adults is reproduction. It’s very unlikely that the BSF are entering your house as adults; it’s much more likely they’re crawling in as larvae and then pupating. You need to find out how the larvae are entering your basement. The following link is a reply I gave someone else with BSF in a basement. The details might be different for you but the answer may be helpful anyway: http://blacksoldierflyblog.com/2008/06/13/bsf-not-vectors-human-pathogens/comment-page-1/#comment-971

Thanks

I’m building a v2.1 unit as I type. I’m taking more detailed photos than before and I’ll post a parts list very soon.

Do you have a place on your blog that lists the supplies needed to build the composter? I’ve seen pictures and illustrations, but I haven’t located the list of needed materials yet. I thought it would be best to start with all the needed supplies before I try to build one.

thanks so much!

Kristi

First, the larvae must be developing somewhere on an adequate food source which is usually rotting food. If you have a compost pile or worm bin near the house that might be the source. Because they need a good quantity of food over a period of weeks before they can fully grow it’s not at all likely they’re maturing inside your house. Once matured the larvae crawl away from the food source in search of a safe dry place to pupate. They head out in a random direction (I assume) and some of them will end up crawling towards your house. Of course at that point they would need to find a crack to enter the house.

One other possibility exists since you’re finding them in the bathroom. BSF will breed in human waste and they might be finding a way to enter your septic system. In theory if the larvae are developing in your septic tank or waste pipes they could be crawling through the pipes and entering the bathroom via the toilet, sink or bathtub drains. They would have no problem passing through flooded sections of pipe. You see, it’s possible they could enter the septic/drain system through a small opening because when they first hatch they’re very tiny. Once they grow to their full size they might not have any other exit than through the pipes and into your bathroom. The BSF females are good at locating waste and if they’re finding even a small opening in the septic system they can lay their eggs on the outside of it and the newly hatched larvae will crawl inside and develop. If you’re finding them in the tub or sink I would think this is the situation.

All you need to do to stop the intrusion is to find and seal whatever openings are allowing the larvae to enter the house directly or through the waste pipes.

I’ll bet the BSF larvae in your basement aren’t dead but are pupating instead. That would explain the adults in your TV room. Don’t get me wrong; BSF do sometimes go into houses but it’s unintentional because they don’t eat and only target rotting food and manure for egg laying sites. If a BSF does find itself in a house it will immediately try to escape. The kind thing to do is to gently catch it in a cup and release it outdoors. If you’re concerned about them laying eggs in your house you can relax; they only want to get outside to find a mate. Even if an egg laden female found her way into your house she would only lay eggs on rotting food, not fresh.

As far as the BSF in your house being “not pleasant” I must disagree. BSF are beautiful, harmless and beneficial creatures, not something repulsive. Each person is entitled to their opinion but this is, after all, the black soldier fly blog…

I think that BSF larvae are migrating away from your compost bin and finding a way into your house where they’re pupating and emerging as adults. I recommend finding and plugging the gaps that the larvae are using to enter your basement.