Running Out of Fruit Flies: What to Do When You’re in a Jam

By Allen Booth and Derick Michael

Allen has 30+ years in the exotics industry. Derick runs MLE's dart frog breeding program in New Jersey.

For the first few years I kept dart frogs, my fruit fly cultures crashed constantly.

Not occasionally. Constantly. I'd find a culture dead on a feeding day and have no idea why, because the one next to it made from the same mix on the same afternoon was fine. I'd change something, and things would get better for a month, and then they'd get worse again, and I couldn't tell you if what I changed had anything to do with either.

I don't crash anymore. But I want to be honest about how that happened, because it wasn't a recipe and it wasn't a moment where I figured it out.

The part nobody puts in the article

Almost everything written about fruit fly cultures is about the recipe. What media, what ratio, what yeast, what magic ingredient somebody swears by. People go down that rabbit hole for years. I did.

The recipe was never my problem. Once you've got one that works, it's close to the least interesting part of this. Everything that actually decides whether you've got flies on feeding day happens around the recipe: where the cultures sit, what light hits them, what you mix into new ones, and how much margin you're carrying.

I didn't work that out on my own. I got it from other breeders, plus a lot of getting it wrong.

How I actually learned this

Here's the thing that changed everything, and it's going to sound like a sales pitch, so let me get that out of the way first: yes, I'm a breeder telling you to buy from breeders. I know how it sounds. It's still how it happened.

I'd drive out to buy a frog from someone local. And then I'd stay for three hours.

That's it. That's the whole secret. Nobody's going to explain their culture rotation to you in a forum thread. But standing in someone's frog room, looking at their shelves, asking why that rack is over there and not next to the other one, with no line behind you and nowhere either of you needs to be, people will tell you everything. The frog was the excuse. The conversation was the thing I actually drove there for, I just didn't know it the first few times.

Forums help. Social media helps. But it's a different kind of knowledge that comes out when someone's showing you their actual setup.

So if you're near us, come get a frog and stay a while. We like making friends in this hobby, and honestly that's most of the fun of it.

What I was doing wrong

Looking back, I did none of what's below.

• Everything lived in one spot. New cultures, producing cultures, spent cultures, all together on the same shelf. So when mites showed up, they showed up everywhere.
• I didn't have a formula locked down. I was still fiddling with it, which meant when a batch went bad I never knew whether it was the media or something else entirely. Nothing was ever a controlled variable.
• I ordered from wherever. Different sources, different quality, no baseline to compare anything to.

None of the fixes are complicated. It's just discipline in places I didn't know mattered, and I didn't know they mattered because nobody had told me yet.

Get a mix that works, then leave it alone

If you're starting out, buy a premade mix you know is good. Plenty of companies make them, us included. Get consistent yields first, before you start experimenting with anything.

Once you're producing regularly and getting good numbers, then go ahead and work on your own mix. But don't wait until you're running low on premade mix to start. That's how you end up in a jam. Do your experimenting while you've still got good premade mix producing in the background, so a failed batch costs you nothing but the container.

And once you find something that works, purchased or your own, stick with it. I'm not getting into recipes here. It's a rabbit hole and it's not where the wins are.

Two things about setup

Media and water

Too little media is a problem. Too much never is. Don't be scared to add a bit more than the formula says.

Water is where the real risk is. Add too much and the culture goes soft, and then when you go to pour it you get liquid coming out with the flies. It might still produce, but it's genuinely unpleasant to use. You learn over time how much is too much, and erring dry is a much smaller mistake than erring wet.

Excelsior

More surface area means more flies. That's the whole principle. It's why we fill our cultures with excelsior almost to the top. The larvae and flies need somewhere to go, and the more of it you give them, the bigger the boom.

We buy excelsior in bulk now so that's what we use, but we used coffee filters for a long time and they work fine. If you're keeping costs down, that's a real option, not a compromise you should feel bad about.

The stuff that actually fixed it

Mix old cultures in, not just the booming ones

This one came from another breeder and it's probably the single most useful thing anyone's told me about flies.

Most people take their newest booming culture and shake flies from it into the new ones. That's what I did for years. Now we go old first, booming second. We keep the older cultures around — past their peak, still putting out some flies — and we mix whatever we can get out of those in first. Then we top up from the booming ones.

Some days that's a lot of old flies, some days it's a handful. There's no number to it. But we always do it.

Why it works, as best we can tell: you get flies at different life stages going in, and a wider genetic pool. Newly-producing flies take time to start producing themselves, and mixing older ones in seems to get the larvae moving faster.

Separate everything into zones

Also from other breeders, and this is a big one.

Our cultures move through three different spots in the room as they age. Not shelves next to each other — actually different spots, away from each other.

• Spot 1: new cultures, waiting to produce.
• Spot 2: once it's booming, it moves here.
• Spot 3: once we've used a good amount and we're waiting on the second boom, it moves again.

It's all about mites. If the old cultures never sit near the new ones, mites can't walk from one to the other. We haven't had mites take over the new cultures once since we started doing this. It costs nothing but discipline and it's probably the highest-value thing on this list.

Light — this one I found by accident

Everything else here I got from someone. This one I found the hard way, and it's a good example of what figuring things out alone actually looks like.

We had a window letting a bit of direct light in during the mornings. It wasn't even hitting the cultures — just nearby, for a little while each day. And the cultures produced, but they never boomed. I couldn't work out why. That went on for a long time.

We covered the window and it was a completely different story. Booms and booms.

They want darkness. We haven't tried full darkness and I'm not going to tell you to, because we haven't tested it. But finding a spot away from the sun and away from your terrarium lights was a real turning point for us.

Temperature

Good news: flies want roughly what we want and what our frogs want. Around 72 to 78°F (22 to 26°C).

The closer you hold 75 to 77°F (24 to 25°C), the better your yields. Above 80°F (27°C) they slow down, and the higher you go the more likely they crash. And that's not one culture — that's potentially all of them at once, which is exactly the thing worth engineering against.

We've never dealt with really cold because we run backup generators, so I can't tell you where the bottom is.

The bucket rig

I'm not going to pretend we've solved flies escaping from terrariums. If you've figured that one out, please tell me. But we've cut way down on the ones that get loose during feeding.

• Start with a bucket. We use a Home Depot blue one.
• Three deli cups go inside it.
• On top of those, the deli cup you're actually feeding from.
• Vitamins go in the top cup.
• Take a culture, shake it up, and only peel back a small section of the lid — don't take the whole thing off. Shake it into the top cup. Next culture, same thing.

Anything that misses lands in the three cups below, and you just shake those into the main cup at the end. A few will miss everything and end up loose in the bucket — take those outside and shake them out. Those flies are free. It's normally just a few, but if you leave them they'll climb out.

When we actually feed, we don't just open the door and pour from the deli container — it's far too easy to overfeed that way. We shake some into a small plastic container first to get the measurement, then put them in. Easier to place them where you want, much harder to overdo it.

And don't forget the banana trick. If you read the other article you know what that is.

Reading a culture

Larvae climbing, and lots of them. That's the main tell that things are going well.

The real trick is comparison, and it only works because we make cultures in batches. Everything made the same day should be doing roughly the same thing. So if one's behind its siblings from that date, I see it immediately. It's a built-in control group.

Here's the part that surprises people: I don't do anything about it. A lagging culture will still probably give me some flies. It's not a crisis and it doesn't need rescuing. It is what it is, and there's plenty else producing.

Which is the whole point.

You don't prevent crashes. You make them not matter.

Look back at that list. None of it is a clever recipe. It's: keep old and new apart, mix broadly, keep it dark, hold your temperature, and always make more than you need.

I didn't get better at predicting failures. Cultures still go bad on me. The difference is that a bad culture used to be a crisis and now it's a Tuesday, because there's always something else coming. That's it. That's the entire thing I got from those three-hour conversations in other people's frog rooms.

It's the same test from the other article: when you're done feeding your frogs and done making new cultures, have you still got flies left over? If yes, a crash is an inconvenience. If no, a crash is an emergency.