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Methods for sorting mealworms

If a person does what they can to keep their stages separate, how would they go about doing so? I have heard from many sources that you are supposed to put a screen on the bottom of your beetle bin so you can collect the eggs, but what is the best size of screen to use without losing too much bedding? People always say keep the frass from the beetles, as it has eggs and larvae in it, so is the frass harmful to the eggs/hatchlings, and could it be separated from them without losing any or harming the eggs/larvae (how fine of mesh is required)? When do the offspring of the beetles need bedding/vegetation?

Someone on youtube was able to sieve out his mealworms from his beetles and pupae using size 6 mesh, the pupae and beetles were chubby enough to stay in the sieve, and the mealworms were narrow enough to slip through the sieve. I saw a mesh sizing chart online, and size 6 mesh has holes that are 3.35 mm in diameter, but I am only able to find mesh that is 3.15 mm in diameter and the holes in that are diamond not square so maybe the mealworms might not pass through that, which would not be good. Anyway size 6 mesh seems to be the magic number and I cant seem to find any anywhere thats exactly size 6. Does anyone know of any good sources for mesh that is labeled by size?

Do people sieve their mealworms based on size if they are seeing too much size variation, or would this add extra unnecessary labor? Are the mealworms from the same batch smaller because they are younger?

I am getting 1000 mealworms tomorrow in the mail, so prep is the next step!

I intend to make an auto sieve further down the road, something that would slowly funnel the worms/bedding into a jiggling sieve pan.

Any advice would be much appreciated.


  • Hi NukedPenguin, -- 1st off allow me to ask if you are planning to use the mesh grow bag method before give my idea on how to finesse stages. You don't have to be going with a mesh tactic but it simplifies things in my opinion.

    Since you are only getting mealworms right now (imminently anyway) when they arrive put them into any container with bran (wheat bran is convenient to use have it) & a slab of carrot (or suitable alternative on hand). Assuming these are not baby mealworms & are fairly old (unless you specified them sized small) the mealworms will pupate into beetle with or without intervening tactics.

    Beyond the step of waiting for pupation you begin to deal in options. Once there are beetles & they have darkened in the bran the whole mass can be sifted through a kitchen collander. The bran, frass & eggs will pass through your 3.1 mm sieve (about 1/8th inch space) while the adult beetles will remain in the collander - the shape being diamond should be irrelevant to holding back the beetles.

    If you go with a design where beetles breed atop a screen to let eggs/frass drop through the that screen to achieve an automatic collection then the underlying screen has to be finer than 3.1mm (1/8in.) because the churning of the beetles will sift dry wheat bran through the holes. Incidentally, at 3.5 mm the #6 mesh is wider than the usual plastic kittchen collander's 3.1 mm so a lot of bran would drop through that.

    Wheat bran is anywhere from 1 (0.4 in.) - 2 mm (0.8 in.; for orientation 1/32 in. = 0.8 mm & 1/16 in. = 1.6 mm) but the eggs & frass are small. A yellow mealworm egg is about 1.25 mm (as per Australia's In terms of a mesh that would preserve bran among the mating beetles & yet let eggs/frass sift through the #18 mesh is 1.4 mm.

  • Hey gringojay, Thanks for all the info. I got the mealworms about 9 hours ago, and I didn't really count them, but it looked like I only got half of the thousand I ordered from fluker farms. Anyway, now that they are here it will have to do. I actually have spent the past week obsessing over how I'm gonna go about raising them. To answer your first question, I am going with a grow bag idea, using a pain strainer, my dad is a painter so that is really convenient. I tied a few rungs of twine around a medium sized plastic bin (for frass) to prop the bag up, and I threw some wheat bran in there, as well as nice big swiss chard leaf, and they are munching it.

    I did make sure I got rid of all the crap people get from a shipment, and I managed to find about 7 pupa.

    Would a 1/8 inch screen allow a larva to fall through but not a pupa? I found something perfect and cheap online I could buy for pupa sorting, as well as a 1x2ft #18 wire mesh for $17 (pricey for the purpose of egg sorting, but it was hard to find)

  • Hi Nukedpenguin, - Before continuing let me edit a correction of my error that 1.4 mm size holes are not #18 mesh but rather what would be called a "US Sieve Size" #14 (as does the nd in the other nomenclature system called "Tyler Equivalent #12 mesh"). My mistake was due to laptop freezing up & without reviewing text I switched to my Nook for submitting the write up. (I also see that I misquoted your 3.35 mm for #6 size as mistakenly 3.5mm, but that doesn't see to alter the context I used it in.)

    So, since there are different systems please refer to this chart with 3 nomenclatures. I think your wire seller will actually be referencing the "Market Grade" classification; at 0.7 mm & 0.5 mm that numbering differs from US Sieve numbering if you go to buy in that size. Anyway link =

    As regards adult harvesting here's what I found with 2 serviceable plastic strainers in my home. These dimensions are suitable for a size of larvae that are just at the cusp of pupation. Measuring done for hole sizes used a flexible little tape measure with markings for each 1/10th of a centimeter.

    Those larvae were able to pass through both square & round perforations of 3/10th of a centimeter (~ 1/8th inch = 3.17 mm). That is once they get their head facing downward into a hole & start to squirm around to fall out.

    The other collander ($5 Target) has the same 3/10th cm holes at it's bottom & also has larger round holes going up it's side which are 4/10th of a centimeter (~ 3/16th inch). The side holes allowed the same larval age-mates to drop right through & those getting their heads into the narrower bottom holes were just slower wriggling through .

    As for pupae they are not all the same size & a decent example has a "shoulder" width of a bit more than 4/10th of a centimenter (~ a bit less than 3/16th in.). The actual pupae wouldn't pass through a 1/8th screen (3.2 mm) which you asked about. And since #6 holes in Sieve/Tyler/Market are all the same 3.35 mm most pupae would not slip through that either.

    What I do find is that when I let late stage larvae sieve themselves through my collander they are sometimes going through as larvae & then pupating after they dropped down into the jumble below. You can pick those out of course. What did you find online for pupae "sorting" ?

    If you are talking about the A5 common paint strainer of 226 microns the reference chart linked puts that in between US Sieve sizes #10 & #8 (Tyler #s differ) being 2 - 2.4mm spread. The frass can fall through that size hole. You apparently have large larvae, however going forward bear in mind Tiny-Farms grow bag instructions caution making sure newly hatched worms "...are large enough to be contained by the fine mesh."

  • edited August 2014

    Thats great that you have found a way of sorting that works, do you just pile them in your strainer and let them strain themselves without you shaking?

    I actually own 5 different grow-type bags that range from 25-220 microns, but I avoided using those because the set is expensive. What size micron mesh is needed to keep in the hatchlings/eggs, letting frass out? Since the worms are so big I did opt for the cheap paint strainer, but I do want to keep the same living model for the hatchlings. Would beetles benefit too from a bag approach?

    The best pupa sorting video is here: and he talks about it at about 1 minute in the video.

  • @Nukedpenguin - we have been successful using 1/8" mesh screen to separate mealworms from pupae and beetles. We stretched a sheet of 1/8" HDPE onto a wooden frame and find that gently shaking or vibrating it will cause the larvae to quickly crawl down through the mesh and drop into a container below. sometimes small beetles will work their way through the holes as well, but few enough that they can be easily picked out.

    In the past we have successfully prototyped a few types of air-powered devices to separate the insects from the wheatbran/frass for final harvesting. Unfortunately we have not had the time to productize the designs and share them here. This is on our to-do list though!

  • Hi Nakedpenguin, - For frass fall through I believe Tiny-Farm growbags use a no-see-um polyester (?) weave cloth but do not know it's hole size. Again the nomenclature sellers provide is confusing. Maybe our Forum hosts can clarify what they use.

    Univ. of Fla. says no-see-ums go through #16 mesh & mentions better a #30 mesh. I believe that is on the "Market Grade" scale of holes. The confusion here is they are referring to fiberglass/metal window screening. Camping equipment talks about no-see-um netting having "x" holes/square inch; then again they sell different fabrics & different weaves .

    Now you are talking about micron hole dimensions from paint strainer jargon. And your widest hole is 220 microns. Refering to yesterdays linked chart 231 microns (0.231 mm) in Market Grade screening scale is #60 mesh & I personally can not vouch for frass passing through that size of a hole.

    At this point I am unclear what size your "cheap paint strainer" is. Whatever size holes you end up using you may wish to reconsider a one size mesh for all the life cycles.

    Since I began using the Tiny-Farm grow bags I have followed their kit's instructions, namely: to separate the breeding beetles from their mating bin after at least a week of potential mating & give the breeders a new bin to try again. The eggs are left in the medium (bran) they got laid in, given time to hatch & once hatched stay there in the same bran for at least another week to let them get big enough before settling the "hatchlings" into a grow bag.

    Australian link said eggs are 1.25mm & websites say are size of a grain of sand; but sand size ranges a lot. Others say the mealworm egg is size of the period at the end of the sentence; but never specify the print font size. Once you know what size the opening Tiny-Farms grow bags use figure on using a smaller opening if want to design yourself a grow bag eggs & hatchlings can't fall through (maybe the opening size is specified on "their" Wicki page, but I don't know).

  • @gringojay @Nukedpenguin - this is the no-see-um mesh we've been using recently, unfortunately mesh size is not specified. Our original experiments used strainer bags, but I can't recall the mesh size.

    A note about the eggs - they are sticky when laid and will cling to substrate (i.e. wheat bran), the sides of containers, pieces of carrot, etc. When beetles have been laying in a clear plastic tub, many of the eggs are often visible if you look up through the underside of the container, stuck the to bottom.

    I personally suspect that the methods that call for setting mesh under the breeding beetles to filter out the eggs may actually be filtering out tiny newly hatched worms that crawl down through the mesh, since the eggs (although tiny) are fairly large relative to a mesh that would filter frass but not substrate - and sticky so they would cling to larger substrate types like rolled oats. However we have not conducted experiments to confirm or deny.

  • I just found out that no-see-um mesh has to be 600 microns (0.6mm) to protect against biting flies, while netting that only protects against mosquitos has to be 1.2mm, according to wikipedia. That netting is really cheap, I'm gonna get some for my future generations. Hopefully, freshly hatched larva are not smaller than 600 microns in diameter.

    I am theorizing that the larva inside the egg must be curled up in order to fit, and the egg shell may be 50 microns in thickness, while the larva's head and tail occupy the 1200 micron void. If my theory is correct, then the larva might be able to squeeze out of the mosquito net with their soft bodies combined with the stretchy nature of many meshes.

  • Egg size becomes less uniform & in some cases smaller as the female beetle ages in it's productive lifespan. Her oocytes age & micro-tubules weaken during meiosis. Another factor is any DNA repair outcome(s) over time leads influences affecting the germ cells & in a series of linkages her somatic cells. (Male sperm of course has it's own age related features.)

    Andrew's "sticky" eggs comes from a γ-proteobacterial symbiont called Ishikawaella capsulata. When actually egg laying the female excretes some from where the symbiont is "doing it's thing" in her gut & it goes on the egg surface.

    Insect eggs without their symbiont that go on to hatch apparently grow poorly in their nymph stage. Which, to me, is another reason not to have eggs try to drop through a mesh - it might scrape off their outer symbiont.

  • So in other words, you are saying cycling out the beetles by hand every 2-4 weeks is the best way to go (while keeping them in a container with no holes in the bottom)?

    By the way, last night after my dad told me to put my mealworm bag in a cat carrier in case of a raccoon, I had a nightmare about my mealworms getting out due to my carelessness, but you know how extreme dreams can be, they were all on the floor under my bed (while I actually keep them in the back of the garage). After waking up, my initial fears became a reality, they managed to chew a couple small holes out of the paint strainer, and luckily only like 20 escaped, and they couldn't leave the cat carrier. I hope the no-see-um mosquito net is more durable than those paint strainers.

  • Hi Nukedpenguin, - Nylon (100%) is what Tiny-Farms mealworm grow bag is sewn from & they reported having to find a non-chewable fabric. Paint strainers are probably polyester/blends.

    Unless you are jumping into a commercial scale it's not that hard to pluck breeder beetles out & place them in a fresh bran container with some radish for moisture. They'll clamber onto your fingers & then can shake them off, but it's not as easy once using a disposible glove.

    I use a plastic tweezer/tong to grab beetles & push around in the bran going after them. Hobby shops sell them cheap for people who do beading & inlays; search on eBay for styles/costs - I like the rounded tip kind for bugs.

    Backtracking: if you're "herding" for personal/pet feed use level then investing in that motorized sifter you linked to on YouTube is not necessary.

  • @Nukedpenguin, dreams are strange indeed, I also had similar when I started. It's possible that you had seen a problem but been too busy to really take it in, or that you had read, but not remembered, that they could chew through. Good catch! I love how dreams exaggerate to get our attention! =D>

  • edited August 2014

    gringojay, is the mosquito net you linked to earlier known to be non-chewable and made of 100% nylon?

    I am not jumping to a commercial scale right off the bat, I plan to mainly just supplement my half dozen hens' diet, by giving them live food. It would be great to be able to give them each a few dozen of them a day eventually, they vacuum them right up.

    I may opt for using tweezers to get those beetles.

    @kerri, I actually remember in my dream that I had been sifting my mealworms into a 5 gallon bucket, and then something grabbed my attention so I walked away mid shake, and next thing you know, they infested under my bed, even though they were by the garage. I just had a sneaking suspicion that they might be able to chew through it, I didn't know that they actually would.

  • Nukedpenguin, - Andrew's link to teams source OnLineFabric says below picture 100% Nylon.

  • Even though seeving the eggs might harm them, I still think this is your way to go. It's also the way I know at least 2 big and 1 small insectfarms do it.

    • You put a steel plate (with holes in it of the appropriate size. Just make them so big that beetles cannot go through) on the bottem of your rearing crate
    • and put some substrate on top of it.
    • Every week you lift the steel plate, shake it so the substrate with the eggs fall through and put the plate with the beetles in a new rearing crate and do the same after another week.

    Congratulations, you now have a clean, larvae -and beetlefree culture of eggs with an age difference of no more then 1 week.

    The same can be done (and is done) to seperate the biggest mealworms from the litte ones. Or to seperate the mealworms from the beetles if you want to collect the newly hatched beetles from your pupation 'crate.'

    Hope this helps you a bit

  • edited November 2014

    For those of you guys that are in search of wire mesh - but are having trouble deciding/figuring out what size you are going to need - why not order some type of mesh assortment? In others words - there are places - or that can sell you a large number of small pieces - different mesh sizes and different wire diameters. This allows you to take a look, and make a decision live in person and test the material before spending a sizeable amount of money on anything.

    Has anyone had any luck cutting this mesh? I tried using scissors, and it just will not cut - do you think wire cutters would work? or some type of sheet metal snips?

  • @penmanship1 - we use long tin-snips like these to easily cut most wire and HDPE meshes:

  • Hey guys, would a polyester mesh work too instead of nylon? So they won't chew through it?

  • Hi Yomanu, - I only have the TinyFarm grow bags, however my inclination is the larger mealworm larvae are capable of chewing any thread fabric such as polyester & cotton in addition to nylon.

  • @gringojay - regarding this comment:

    "Insect eggs without their symbiont that go on to hatch apparently grow poorly in their nymph stage. Which, to me, is another reason not to have eggs try to drop through a mesh - it might scrape off their outer symbiont."

    Today I have my beetles in a solid-bottom bin and once a week I am using a 1/8" wire mesh to sift out the wheat bran and get the beetles, then put the beetles in fresh wheat bran. I then put the sifted bran back in the originating container to hatch.

    My question regarding your statement - you say that mesh bottoms result in dropping and damaging the symbiont is detrimental to the egg, but the alternative method I am using would also be detrimental right? I am shaking the substrate and it is scraping against wire mesh as it falls through, isn't that damaging the eggs as well?

    What methods work best for commercial size? I have 12 bins of 3000 beetles and rotate weekly, I am considering the mesh bottom to save the time of sifting bins each week.

  • Hi MidwestMealworms, - Your 1/8 inch mesh = 3.175 mm & the above Australian citatation gives average mealworm egg as 1.25mm (1/20 inch), so I don't see that eggs have to scrape through. My thinking is that any mesh size which makes sifting go fast enough for the operation to perform efficiently is not using such a small gauge of mesh that a significant number of eggs are affected.

  • That makes sense, thank you @gringojay. I'm wondering if there's a compromise between mesh above substrate and having to sift the beetles every week. What about this idea - a 1/8" mesh on the bottom of a bin (Bin A) that sits inside another bin (Bin B). Bin Bhas 2" of wheat bran, the Bin A sits on top with 2" of wheat bran and beetles.

    Would the beetles lay at the farthest 'down' point they could get, the mesh? If so, if the beetles are left in that wheat bran long enough for the first eggs to hatch, would the newly hatched mealworms have a natural tendency to go 'down' and thus migrate into the lower bin?

    Then, once a week pull Bin A out, place in on top of a new bin with wheat bran, and start another cycle. No sifting of the bran, no dropping of the eggs.

    This is dependent on the mealworms staying 'down' in the bottom bin.


  • I presume some operations use the method of stacked bins for flow-through development. The mealworm eggs are naturally going to become "stuck" on bin walls, floors & substrate (ex: bran); so if not on very small pieces of substrate few should fall through top bin mesh most.

  • Right, the eggs stuck to the bin and mesh and substrate wouldn't fall through if sifted after a week. They'd stay in the beetle bin, and then the following week as they hatch - will the mealworms migrate down to the lower bin, or would they just stay up in the beetle bin?

  • 850 micron (0.03 inch) mesh let newly hatched mealworm larvae fall through for Morales-Ramos' 2012 report; as discussed in Forum thread "beetles per sq. inch". The cited study used a flow-through design similar to what you envision & left bran/beetles up in top bin like you intend.

    Go to bottom of page & click on version "WEB" to get Forum search bar at right of page. Type in "850 micron" & should link to thread; title of Morales-Ramos report is stated if want to track that down.

  • edited April 2018

    Hello to everybody In recent months, i have been intensively engaged in research of the mealworms. That is why I would like to share your conclusions with you. I really thank Andrew for his tip about the reflection of using mesh under beetles. I decided to verify his hypothesis and I must tell that he is right. Earlier i used a 1.3mm mesh under the bugs, but i had very small number of eggs. So I came to the new method. Add about 3cm of flour to the breeding box. To supplement of proteins, I use the dryed wheat sproud that I put on top of the substrate. It may be replaced by the milk powder but it is much expensive. Of course, I add the water source (apple,carrot,potato). After a week i sieved it thrue two meshs. First mesh 2,5mm (you can used from 1.5mm to 3mm) for beetle separation. Next 0.7mm (probably you can use smaller) for egg separation. The separated substrat and beetles return back to breeding box and repeat the process. The result is pure eggs with a small amount of substrate. Because to the whole quantities of the eggs is small quanitities of substrate, you can better to feed by wet food. I add info about measured dimensions:


  • edited April 2018

    Box of separated eggs. 20180413_162602 Size of eggs about 0,7x1,6mm Oddělení vajíček sítem Young worms 0,5x3mm 20180415_115750 Lestor - Libor Sloupenský ;-)

  • Lestor,

    Very interesting! To clarify, you used only flour as your beetle substrate with some dried wheat on top? Why not finely milled wheat bran, that would be a similar texture to flour but is something the worms are known to live in.

    What was the effect on the eggs, did you have the expected population of baby mealworms or were they damaged by the flour and sifting?

  • Awesome that you were able to figure out the mesh sizes to make this work, Lestor. Thank you for sharing! I'm also curious, in addition to potential damage from sifting that MidwestMealworms is asking about, did you notice if there were any eggs stuck to the larger-size mesh or other surfaces?

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