Wednesday, January 28, 2015

Screened Bottoms -- Yea or Nay?

I belong to several groups dedicated to TBH enthusiasts, and the question of the day lately has been, "Do I need a screened bottom on my hive?"

It's always tough for me to answer this question because my first instinct is a nearly irrepressible urge to sing something about screened bottoms to the tune of Queen's "Fat Bottomed Girls." However, once I pull myself together sufficiently to answer, my bottom line answer is that I don't think they're a bad thing. They may even be useful to you depending on your situation and goals. I don't like them myself, but that's a personal preference. My first year of beekeeping, I tried them. The next spring, I ripped out all the screens and replaced them with solid bottom boards (SBBs).

In the spirit of full disclosure, I won't even pretend to be unbiased in my opinions. However, I'll still attempt to outline some of the pros & cons of using screens as objectively as I can.

Integrated Pest Management

One of the main reasons people use screens is as part of an integrated pest management (IPM) system. The thinking is that one installs a screened bottom. #8 hardware cloth is usually recommended for the screen since it's small enough that pests can pass through, but not bees. Below that, one installs a removable/hinged solid bottom that is covered with something sticky like oil or diatomaceous earth (DE). The idea is that pests like small hive beetle (SHB), varroa, and wax moth larvae fall through the screen and get stuck in the oil/DE.
  • People I know who do this say that they trap a lot of pests that way, and they feel that their colonies are healthier as a result. 
  • Screened bottom users feel pest counts provide information about their colonies which they use to decide on treatments. I can see how this information would be interesting. Not sure what to do with it, but it would be interesting to observe any possible correlations over time.

  • Because the bees can't reach the sticky board, they can't clean it out. That means lots of corpses in the hive, and I don't know if/what effect that may have on hive hygiene. 
  • Because bees can't clean the hive, the beek has to periodically clean the icky sticky board. I have an aversion to extra unnecessary work and ick. 
  • IPM screens/sticky boards require more time, energy, and resources to build. 
  • Also, when the colony is really rolling in late spring/summer, you might have trouble closing the sticky board again. I know I did. I opened it, and within minutes, I had massive bearding.
  • Michael Bush claims that IPM systems just trap the klutzes that can't hang on and breed clingier pests. He could be right. I just don't know about that. What I do know is that strong, hygienic colonies are able to take care of pests themselves. If the bees can't survive without being propped up, maybe that's not a colony that should be reproducing.
  • Finally, I'm going to contradict what I said about gleaning info from the sticky board. If you plan to treat, counts are well and good. If you want to be a treatment-free (TF) beek, though, you have to decide if you need a pest count -- because as a TF beek you aren't going to do anything about it anyway. If you have information, you may actually feel pressured to treat the hive or do something to intercept "the problem" in some way. If you don't need the information for any particular purpose, then you've created a lot of work for nothing.
Overall, I would say that I have seen varroa, wax moths, and SHB around/in my hives. However, strong colonies and winter seem to be enough to take care of pests for me. 

BTW, as an aside, after removing the screens and installing SBBs, I noticed earwigs in the hive. While my bees ferociously attack various pests, they tolerate earwigs. Even though I was wigged out, I was fascinated to learn that don't harm bees or honey, and they eat mites that fall to the hive floor. Antlions, which eat ants, are another thing I've noticed around my hives. Hmmm... maybe nature has created its own IPM system. 


I'm going to be upfront. I really don't see any "pros" to using a screened bottom for ventilation, not even if you live in The Deep South (more about that in a minute).

New KTBH beeks are without exception nervous about comb getting too hot and falling off the bars. Therefore, they want to make things cooler for the bees in the summer, and ventilation is probably the most common reason I hear for using screened bottoms. I'm going to be upfront about my opinion. In fact, I honestly can't think of any benefits.

From where I stand, I see how screens might make sense in a Lang because they're built like chimneys. Without a screened bottom, it's probably harder for bees to fan air up and down the column. However, with a screened bottom (and especially if you have a top entrance), hot air rises and simultaneously sucks up cooler air from the bottom. So, ok, I can see how this might help regulate summer temperatures in a Lang. In a TBH, though, bees have an easier time regulating temperatures anyway because air is moving horizontally in a track like in a bathtub, not vertically. 

To me, TBHs are like a squat outdoor tent in summer. I remember going camping when I was a kid and having all the flaps open on the tent. It would be a little cooler inside because we had shade, but overall the inside temperature wasn't that much different from the outside. I see TBHs being the same way. You can leave the bottom open, but I don't think it really cools things off significantly.

My first year, I had screens, and I noticed the bees bearding. What did I do? I did what all people with screened bottoms do -- I opened the bottom so they could get some air. Instead of lessening, though, the bearding got worse. People will say, "Oh, wow, that's so neat! Look at how they cool themselves off!" However, I think they're missing the point. Bees beard because they are uncomfortably hot inside the hive. If the "ventilation" was doing its job, it seems to me the beard should have gotten smaller, not bigger.

The following year, I ripped out the screens and installed SBBs, and I had significantly less bearding. Yes, I know this is not a scientific observation. I have no control or test groups, no data for each year. However, I reason it away like this. Remember, that bees have their own system for air conditioning. They stand around the entrances fanning their wings in order to circulate air and remove moisture from the hive. Now think about it. If you were going to run the air conditioner in your house, would it work better if you had all the windows open or closed?

If you can't tell yet, I've really come to agree with people like Michael Bush and Sam Comfort who say a screened bottom provides too much ventilation. While a large, established colony can deal with it, screened bottoms are the #1 cause that I've heard for new packages absconding. Well-intentioned people install a package and open up the bottom. Within a day or so, their bees are gone because they can't control their climate.

Another downside of screened bottoms that are left open for ventilation is that pests can now climb up through the screen into the hive. If you feed inside the hive and leave the bottom open, you'll also encourage robbing.

But what about comb getting too hot and collapsing? Oh, yeah, back to that... In various exchanges with TBH beeks in hotter areas of the country like Texas, Florida, and the Deep South, I've found that some use screens and some don't. Of the ones that don't use screens, most of them seem to say that they 1) avoid working hives during the hot part of the day which is a good practice anyway if you're in a hot climate 2) some of them keep their hives in partly shaded spots, some of them keep their hives in full sun. Either way, they claim comb collapse has not been a big issue.

Personally, I'm not saying comb doesn't collapse. I know it does because it's happened to me. However, in my cases, heat has not been the issue. My issues were related to cracks that had developed in the comb due to improper handling. Then the comb was filled very rapidly with honey before it had time to harden. As a result, it fell.

I know I've been hard on screened bottoms for ventilation. If you disagree, that's ok. I'd actually welcome your (polite) perspective in the comments. It's always good to have a healthy exchange of differing opinions.

Wrapping Up

Ok, I know that I am strongly biased against screened bottoms myself, but I'm not against other people using them. Whatever floats your boat, I say.

If one is up to the additional work of creating and maintaining an IPM system, a screened bottom with a solid board beneath it could be very interesting. The important thing, from what I've heard, is to not leave the bottom open all the time or to find a way to open only parts of the bottom.

I doubt that leaving the entire bottom open hurts the bees (because I've done it with no ill effect other than lots of pollen dropped on the ground and more wasps nosing around), but I do think it makes the little girls work harder for no good reason. Also, it encourages robbing, and it allows pests to enter through the screen into the hive.

If you're a new beek starting out, you should have two hives anyway. If you're really torn, why not satisfy your own curiosity and get one hive with a screened bottom and one with a SBB? Then you can compare notes and see what you like better. If you do, though, please, share your observations here! I'd love to hear what you think!


  1. I've built screened bottom boards into my 2 TBH's for IPM. It requires a lot of extra work and I still don't have the design worked out quite right. The wide design of the Hardison Hive isn't conducive to adding one (maybe that should have been my first clue!). I put a sticky board under the screen and do periodic mite checks. However, I'm not very good about doing that, so the periodicity is quite low and your post makes me question whether it's worth it. Even if I find some mites, I don't do anything about it (except worry).

    Your comments about earwigs is interesting. I helped a friend set up a Lang last year and the first time we went into the hive for an inspection, it had tons of earwigs in it. He asked me if that was okay and I didn't really know at the time. Since then, I've come to realize that they are okay and will eat the mites on the floorboard.

    I never open the screen for ventilation - I figure they need to cool the hive off themselves. I did put a vent in the back of the hive to improve airflow which seemed to reduce the bearding this past summer - but it was also a cooler summer so maybe that's why they didn't beard. I've had comb collapse, but that's because I did inspections during the heat of the day. I now make my inspections earlier in the day and last year had none collapse.

    Have you seen Phil Chandler's new idea to replace the screened bottom board. He calls it the Eco-Floor:

    After reading your post, I think I'll try this year's new hives without bottom boards. I still like including windows to show my curious visitors what the inside of a hive looks like in a non-invasive way. And I'm getting better at that bit of carpentry. ;-)

    1. That's cool that you're going to build hives with solid bottom boards. Since you'll have hives both with/without screens side by side, I'd love to hear how you think they compare. That would be such an awesome science experiment!

      Thanks for sharing Phil's vid. I've seen it before, and I know that a lot of people on his forum BioBees are proponents of it. I think it's a really neat idea and I can see a lot of benefits from the bees' perspective, but I haven't thought about trying it out personally for a few reasons. 1) Even though I know of lots of people who use them, I haven't heard from any of them whether they think it actually works better or worse than solid bottoms. 2) It seems like more work to make & my skills already leave a lot to be desired 3) My guess is that they must periodically rot out, so they're more work to maintain. 4) Phil recommends against using screen over the ecofloor, but it seems to me that if a comb collapsed for any reason, it would be a right mess to clean up. However, if you use a screen over the floor, I think that would prevent bees from clearing out the dead, which I wouldn't want either.

      Are you going to try an ecofloor on your hive? That would be so cool.

    2. Julie, this is a great discussion. I agree with your arguments and also have come to believe that screened bottoms on top bar hives are not beneficial. We built our tbh's with screened bottoms and last year kept them pretty much closed. The only time I used it was to lower it slightly to allow a crack of ventilation during a time when it was very hot and a dearth was on so I could reduce my entrance without their ventilation suffering.

      Two years ago I pretty much lost a hive because of a robbing episode. The more they were robbed, the more I felt the need to supplement the hive with sugar water in an inside feeder. The robbers can smell the sugar water through the bottom and they increased their robbing.

      Another point that Phil mentions is that trees don't have screened bottoms, so it is another example of man's manipulation for the beekeeper's benefit and not the bee's. Just my 2 cents!

    3. Sue, I really appreciate your anecdote about how feeding with a screened bottom caused robbing which led to more feeding and more robbing... I'm so sorry about your hive. It sounds like a vicious circle that just spiraled downward.

      Out of curiosity, it sounds like you still have screens, so what do you do about feeding now? Do you still feed in the hive? How have you stopped the robbing?

    4. I have not removed the screens, but keep the bottom board closed. This past year I used a jar feeder behind the follower inside the hive with a newly installed swarm, but I made sure the bottom was closed tight. Any time I am feeding, I reduce the entrance(s) to only one hole so they can defend it. Bottom line is I don't want to feed at all unless I feel it is necessary. I plan to harvest no honey until spring if there is any left for me. Sugar-water to me is like taking the fruits and veggies away from your kids and feeding them candy bars! They will eat it, get a lot of energy out of it, but that doesn't make it good for them!!!

  2. I'm not going to try the eco-floor, but I am going to try Phil's hive design this year (sans screened bottom) which will be a first for me. I hadn't thought about your point about a comb collapse into the eco-floor - that would be a mess! When I've had comb collapse in my hives, honey gets onto the board below my screens and it's already a mess. It hasn't led to robbing, but a good thing to keep in mind. The bees do line up trying to get the honey from the board which is quite a sight.


Thank you for your comment! I can't wait to hear what you think!