This season we have spent a lot of time talking about pollinators for the carrots. The basic questions about pollinators seem to be as follows:

  • What insect to use as a pollinator?
  • Where/how to purchase the pollinators?
  • How do you maintain your pollinator population?
  • Can you breed your own pollinator population?

So let’s see how much I can recall and fit into this blog post! This information coems from a variety of sources:

  • Conversations with the current Carrot Seed Project Team, especially from Jen Cody, who bred a healthy population of flies last year, as well as Jeremy Pitchford at Ptichfork Farm and Kristjan Johannson at Sharing Farm
  • Contributions from previous Carrot Seed Project growers Mojave Kaplan and Patrick Steiner
  • My own (Chris Thoreau) experience trying to attract flies to a meat source
  • Various internet resources including Forked Tree Ranch and numerous reptile supply websites and reptile raising forums

So let’s get to it, shall we?

What Insect to use as a Pollinator?

When people think of pollinators often the first insect that comes to mind is the bee. The importance of bees as a pollinator of crops worldwide is indisputable and with one of our growers, Jen Cody, being a beekeeper herself, and with another farm, Sharing Farm, already having beehives onsite – bees might seem like the logical choice.

We had a good discussion about using bees as pollinators, but the main concern was that the enclosures we were using were too small too maintain a healthy bee population and, if the bees are unhappy – nobody will want to get into the enclosure with them! Last year, Jen Cody ordered bumblebees as pollinators for one of her enclosures and promptly named them “Grumbles” as they were quite upset and aggressive after being shipped to her and made it difficult for Jen to get into the enclosure.

Thus, the strategy has been to use the flies, which Jen Cody and Patrick Steiner have had pretty good luck with in previous seasons.

flySo – our insect of choice as a pollinator has become the blue bottle fly – well-known as a pollinator of carrot crops and as a household pest! The blue bottle fly is a good choice because we have the option of buying the pupae or of breeding the flies ourselves. In our case it looks like we will do a combination of both.

Fly Lifecycle

As a little aside, let stake a look at the fly lifecycle, so we know what we’re dealing with.

Adult flies are attracted to food sources, rotting meat being a preferred meal, on which they lay eggs. The eggs hatch within a day or two and the larvae emerge and feed on the food source. After 5-10 days, depending on many factors, including temperature, the flies will move from the food to nearby soil in order to pupate and transform into an adult fly. The pupal stage can be 1-3 weeks. The flies emerge from the pupal stage and are ready to start the lifecycle again – and start pollinating your crops!

Here is how that lifecycle looks in chart form (helpful when breeding):

Day: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
Phase: Attract flies to food Maggots and Feeding Pupal Stage Flies Emerge and Pollinate!


And here is a pretty diagram of the lifecycle:




Where and How to Purchase the Pollinators?

Purchasing flies as a pollinator may be dictated by local availability or by shipping location. The supplier we are using is Forked Tree Ranch, based in Idaho. Forked Tree will ship overnight if an order is made by 9:00 am, but they only ship to Canada two days a week and it will almost always get delayed coming across the border.

Another potential source of pupae is reptile supply stores/websites wherein the flies end use is not as a pollinator but as a meal for pet reptiles! Your choice of source for fly pupae will mostly be based on shipping options and price – and, of course, the quality of the pupae received.

IMG_8691When ordering flies they are shipped in the pupal form. Pupae from Forked Tree Ranch are shipped in an insulated box with an ice pack to keep them cool. This prevents them from hatching en route! In order to get the pupae to hatch simply leave them out at room temperature or above and they will emerge in 1-2 days. Thus, when Forked Tree Ranch is shipping this pupae they must have been in the pupal form for many days already.

So, as you may have deduced, in order to keep your flies in the pupal stage you can simply keep them in the fridge and release them in stages. This would allow you to make one purchase, pay for shipping once, and have all the flies you need for your pollination period.

Except it is not quite that simple. (At least we don’t think so). The folks at Forked Tree Ranch said that if the pupae are kept in the fridge for too long they are more likely to be born without wings – making them pretty useless as a pollinator. They said a maximum time would be two weeks. We have not really tested this claim, but I think we should. I imagine telling folks that the pupae cant be kept in the fridge for too long may equate to more sales for Forked Tree Ranch so testing this might help save us some money. When I asked them about maintaining the population, they didn’t have too much to say about that either – again, not in their best interests!

So a fun winter experiment might be as follows:

  • Purchase 3000 pupae
  • Keep the pupae in the fridge
  • Every 2 days release 2 lots of 50 pupae from the fridge into 2 separate enclosed containers at room temperature
  • Record results
    • Hatching %
    • % without wings
  • And see how things change over a several week period
  • Find a friend with a reptile to feed the flies to!


Releasing Pollinators

You can choose how much pupae to purchase at a time. We purchased 5 cups/grower from Forked Tree Ranch for enclosures which are about 20′ x 10′ in size. The growers released these in 2 batches, though they could be released in 4 batches if you wanted. Whatever you think will work. The goal we are aiming for here is 2 flies per flower for optimal pollination.

If you want to work with just purchased pollinators you can purchase them in batches to coincide with your flowering schedule. They ship very quickly so you can order when you see the first flowers opening.

We ordered our first pollinators to arrive just prior to flowering to ensure the early flowers get pollinated. This coincided with a cooler spell of weather which has delayed the flower opening, but hopefully we can maintain that population as flowers open. We have also done a second order of pupae which arrived today. But from here on out we should be able to maintain the populations we have…

For some reason I can’t find a picture of the enclosures with the flies in them, but they have a strong presence once released. In the enclosures, the flies tended to gravitate to the white plastic corners. When we released them at Pitchfork Farm and Sharing Farm the flowers were just about to burst so the flies were not yet present on flowers, though you could see them sitting on the flowers about to open.


So this should now give you a good start in assessing your pollinator needs and what to expect. For Part II of this post, we will get into the nitty gritty and look at how to attract and breed your own flies. We have a few things to share from our experience as well as many things to consider when taking this route. This method may not be for everyone, but it is not very difficult and makes for a great conversation piece.

Here are a few pictures to prime you for Part II:

Here I am using raw fish sitting on a bed of soil (not a bed of rice) in a clear plastic bin with holes in the side to attract and trap flies. It is a stinky method but very effective for procuring both flies and larvae/pupae:



Here are I am using a small amount of ground beef to attract flies and encourage them to lay eggs. This method had very little smell – I did it on my balcony in the middle of the city:



If you have any comments or questions, please leave them below and we will respond here to have a continuous record.