Houseflies & ants are usually attracted to the BSF box because of the smell of the foods for them. As the houseflies lay eggs on the food, their little maggots will also attract ants. Let's see some simple way to keep your BSF box BSF-only.
Keeping houseflies away
When do houseflies usually occur?
Houseflies usually come around most at the beginning & ending stages of the black soldier fly larvae growth. Specifically, the first stage when the eggs are hatching & the last stage of the pre-pupae before they turn black.
At the first stage, there is an abundance of food for them. As the BSF larvae are now very tiny, the houseflies may think there will be enough food to share for her babies too. So they come. And near the pre-pupae stage, the darkened larvae will eat less. This suggests extra food & it attracts the houseflies.
First step to keep houseflies away
What we can do is to start off with a little bit amount of food first. This prevents it from getting moldy before the BSF larvae can eat it. It also keeps the food amount just enough for the BSF without too much excess. Make sure the box is well-ventilated. This helps create an environment with lots of oxygen, which houseflies don't usually like. They seem to prefer an anaerobic environment with more foul smell.
One way to reduce the foul smell
It's recommended that we pre-treat the foods with some microbial enzymes or ferment them before putting in the box. This helps get rid of the smell which could attract houseflies. Lime may also work to minimize the little housefly maggots. Also, you can try covering the box with a lid or a piece of cloth or burlap. This provides good shade for the light-sensitive BSF larvae & keeps the guys we don't want away.
As your BSF population gets more crowded
Once your BSF colony is more established, the larvae themselves will be the natural fighters against houseflies. As they get more crowded, the grubs will excrete more of a type of pheromone, especially when they're chewing foods. This pheromone keeps the houseflies away. During the first 1 or 2 weeks, you may see some houseflies around. But when your colony is building up, you'll see the houseflies naturally disappear. There's no more room & no more food for the flies or her babies to survive. So she leaves.
Dealing with ants
Ants may appear because of the sugars in the foods like an apple & so on. It may also be a sign that the houseflies have successfully laid their eggs around the box. Because ants love & fight for their little maggots. The drastic approach to controlling ants is to spray some anti-ant solution around the box. This method helps stop the ants quickly but the chemicals may have effects on the young BSF larvae.
Another way to keep the ants away
To keep ants out, try some feeding stations or ant traps on the four legs of your BSF box. In a bowl or so, mix in some sugary water or black oil. These divert their attention from the BSF box. If we do it the drastic way, mix in some boric acid. When this stuff is carried back to the queen, it can get their whole colony destroyed. But I hope we don't need to go this far.
Also, like before, start off with a small amount of food first. Then, slowly work your way up as your BSF grubs grow bigger. As we already know, nature leaves nothing to waste & any excess food in the bin will definitely attract one or two visitors.
Have you tried the eco-enzyme stuff?
Eco-enzyme (or garbage enzyme) also helps keep ants away effectively & it's much milder than some strong solutions. It's also super easy & cheap to make. In a box or bucket, mix in a 1:10:3 ratio of 1 part sugar : 10 parts water : 3 parts food scraps of your choice.
The 3 parts can be left-over foods or fruits. Citrus is great for this because of the terpene in their rinds. Let the mix ferment in a dry, cool place. Remember to open the lid to let the CO2 out so the pressure doesn't crack the container. In about 2 months, you can get some of that juice to spray around your BSF box. You'll see much fewer ants.
If you have raised some BSF before, the leachate (or effluent discharged from the bin mixed with the undigested foods + outer skins + their castings works great to discourage ants from marching around your box. It's also effective to keep the houseflies far away.
When your black soldier flies army grows bigger, they will have the natural defense against ants as well as other insects or wasps. The smell they gives off is like 'This is our yard now. And you don't want to mess with us.'
Now we know some of the ways to tackle the houseflies & ants problem. Hope this brief post has given you some ideas on the topic. Again, don't worry too much because after some time raising BSF, the houseflies & ants will naturally decrease in population as your colony population increases.
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