Housefly larvae are usually much smaller than black soldier flies larvae. The housefly maggots writhe & wiggle in a slightly faster and more erratic movement–like a zigzag line. Whereas the BSF larvae inch forward & around like a softer wave and the movement of a caterpillar.

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Little cream housefly larvae

Comparing housefly & BSF movement, we can see that:

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Housefly's movement video:

Black soldier fly's movement video:

The housefly larvae we're seeing above are only 1 or 2 days old. Compared to days-old BSF larvae, these guys are smaller. You can see the size difference here:

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Let's see another comparison:

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Housefly larvae vs BSF larvae

Even if we leave the housefly larvae to grow into bigger pupae, they'll still be tiny compared to the BSF pupae. The housefly pupae size are like little black beans or grains whereas the BSF pupae are about an inch or so with more visible stripes on their bodies.

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BSF pupae vs Housefly pupae comparison

As adults, houseflies lay their eggs directly on food scraps while black soldier flies don't. They lay their eggs adjacent to the food scraps–between tree gaps or small crevices.

BSF vs Houseflies: Different biology & living environment

Houseflies do well in a wider temperature range compared to black soldier flies. You'll see them more often in cooler times than the BSF. They love a more anaerobic environment with less oxygen. They reproduce fast & have a shorter life cycle than black soldier flies. For example, houseflies like places with stinky food stuff, more wet or have a more foul smell.

Black soldier flies, in contrast, do better in a more dry or slightly moist environment. They like a more aerobic place with plenty of oxygen to breathe, to exchange gases & to dissipate the heat. The places BSF larvae usually feed on have a less foul smell because of the steady oxygen supply. Sometimes, it even smells nice–like that of over-ripe fruits but not the yucky puke smell.

When houseflies may occur around your BSF bin

When you're first starting your BSF colony, you may see houseflies visiting for the first 1-2.5 weeks. This is totally normal because the smell of the foods keeps them coming. Make sure not to leave too much excess foods in the bin. Just leave enough to establish your BSF population first.

When they are more crowded, the BSF larvae will actually shoo out the houseflies. They have a special pheromone/antibiotic for this job. From week 3 on, you will see much fewer houseflies around. After some time raising the BSF, the population of houseflies, insects or ants near by may naturally decrease as the BSF take over.

As you can see from the pictures above, the houseflies usually occur during the larvae stage (cream larvae) & the pupae stage (black pupae). If this is a serious problem, try some microbial enzymes to spray them at the pupae stage. This enzyme kills off the housefly pupae while still keeping your BSF pupae alive.

If you'd like more info on how to keep houseflies or insects away from the BSF box, check out this post below with some helpful tips:

How to keep houseflies & ants away from black soldier flies compost box
Houseflies & ants are usually attracted to the BSF box because of the smell ofthe foods for them. As the houseflies lay eggs on the food, their little maggotswill also attract ants. Let’s see some simple way to keep your BSF box BSF-only. HousefliesHouseflies usually come around most at the begi…

Hope this brief post has given you some ideas on how to identify houseflies and black soldier flies. With that said, have a good time raising and composting.

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