The solid floor as the colony's mirror: reading the drop and the nest

In the age of open mesh floors, cameras and sensors it is easy to forget that the oldest and cheapest diagnostic tool a beekeeper has is right under their nose, literally. It is the hive floor and what collects on it. I myself run solid floors, without mesh, precisely because a solid floor is like a mirror of the colony. Before I even take the nest apart, a single glance at what lies on the floor and the tray tells me a lot about what is going on inside. It is a skill you cannot buy in a shop, one that comes from looking and comparing.

This article develops a thread that ran through the one on varroa treatment: that diagnosis is not only numbers, but also reading signs. I want to show what exactly the drop and the mess on the floor say, so you start seeing the floor as the colony's information sheet, not as something to clean up.

Why a solid floor rather than an open mesh one

An open mesh floor simplifies one specific task: counting the varroa drop, because the mites fall through the mesh where the bees cannot reach them. It is convenient, and I wrote about it separately. But a mesh floor has a drawback: it cuts you off from the rest of the information. Everything the bees carry out of the nest, that is crumbs, cappings, dead bees, traces of disease, drops through the mesh and lands out of sight or on the ground.

A solid floor collects it all in one place. True, the raw varroa drop on it is understated, because bees and ants clear some of it, and that correction has to be kept in mind. But in return you get the full picture of what the colony throws out of itself. For me that information is worth as much as the mite drop itself, which is why I deliberately stay with solid floors. It is a matter of working style, not dogma: a mesh floor gives a cleaner measurement of one thing, a solid one gives a broader picture of the whole.

In season a clean floor is the norm, mess is a signal

Before we get to reading the drop, one rule that orders this whole diagnosis. In the height of the season, when the colony is strong and efficient, the floor should be essentially clean. A healthy, vigorous colony is an army of cleaners that carry out of the hive everything they can and keep the floor almost scrubbed. This is the normal state you get used to.

And that is precisely why the floor is such a sensitive instrument: since in season it should be clean, anything that appears on it is a signal. A shower of cappings, a heap of fresh corpses, ejected brood, crumbs in an unusual place, all of it stands out against the clean background and says: look. In summer, then, you do not read the floor as if studying a densely written page, but as a clean surface on which something has suddenly appeared. This changes only in autumn and winter, when the colony weakens, stops cleaning, and debris from uncapped stores and the winter drop naturally collects on the floor. Then you read differently, because mess is expected, and what counts is its kind and distribution.

What the varroa drop says

Let us start with what most people look at the floor for at all. The mite drop, that is the number of varroa falling per day, is the basic trend indicator. You slide in a tray, on a solid floor it is worth smearing it lightly with petroleum jelly so the mites stick and no one clears them away, leave it a few days, then count and divide by the number of days.

The drop itself tells you the direction: rising or falling, calm or sudden. A low, steady drop is a good sign. A rising one from week to week is a signal that the varroa population is picking up. A high drop is a red light. Especially valuable is the drop after treatment, because it is the most honest proof that the product worked. The thresholds and numbers I set out in the article on varroa treatment; here the idea itself matters: the drop is a thermometer you look at regularly, not once a year.

It is also worth looking at the mites themselves on the tray. If quite a few are chewed, damaged, with legs torn off, it is a sign the bees are grooming, that is cleaning themselves of varroa. It is a trait you want in the apiary, so such an observation is not a curiosity but a breeding hint.

What the rest of the drop says

And here begins what a mesh floor will not show you. Besides mites, the whole story of the colony lands on the floor.

Wax cappings. Fine cell caps on the floor are a normal effect of brood emerging and stores being uncapped. Their distribution and quantity tell you where and how intensely the colony is working. A sudden shower of cappings in an unusual place or at an unusual time calls for a closer look.

Crumbs and wax debris. Fresh, pale crumbs are a sign the bees are building. A lot of debris from uncapped stores in late autumn or winter says the colony is using its stores, and where the cluster is sitting, because the crumb drop settles beneath it.

Dead bees and their state. A few dead bees is normal, because the colony is constantly turning over generations. But their number and appearance carry information. Many fresh corpses is a warning sign. Dead bees with tongues extended may point to poisoning. Deformed bees, with twisted wings, are the face of advanced varroa and deformed wing virus. Dark, hairless, shiny individuals suggest chronic paralysis.

Ejected brood. Larvae or pupae on the floor are always a signal to pay attention. It may be a symptom of hygiene, when the bees remove varroa-infested or sick brood, which is actually a desirable trait. But it may also be a sign of brood disease, a queen problem or starvation. Ejected brood does not diagnose on its own, it calls for a deeper look.

Traces of intruders. Mouse droppings, remains of a nest, chewed combs on the floor are a clear signal that someone uninvited has moved in. Then the matter is simple and urgent.

Mould, moisture and smell

The floor is also a barometer of nest conditions. Mould on the floor and on the lower edges of the combs is a sign there is too much damp and too little airflow in the hive, which is especially dangerous in winter. A wet, steamed-up floor says the same. It is a signal to improve ventilation, because moisture kills bees more effectively than frost.

Smell counts too. A healthy nest smells of wax and honey. A sour, putrid or unpleasant smell rising from the floor or entrance is a reason to look at the colony more closely, because it may herald a problem with stores, brood or disease.

Not everything on the floor is an enemy: tenants that help

On a solid floor, in the cracks and under the drop, creatures can settle that most beekeepers do not know and that play on our side. The most important is the book scorpion, the pseudoscorpion, in Latin Chelifer cancroides, a tiny arachnid looking like a minute scorpion without a tail, a few millimetres in size. It was once even called the mite wolf, because it hunts small arthropods, varroa among them.

This is not folk legend. PCR studies confirmed that in the hive book scorpions really do eat varroa: mite DNA could be detected from their bodies up to four weeks after a meal, and under camera they hunted varroa while ignoring the bee brood. Mentions of book scorpions as allies of bees appear in the literature going back over a hundred years.

There is a flip side, though, and it has to be stated honestly. The book scorpion has practically vanished from modern hives, because smooth, tight interiors, regularly scraped of propolis and treated with chemicals, give it nowhere to live and nothing to eat between varroa surges. Nor has anyone shown that on its own it keeps infestation in check, because there is simply too little of it. So treat it as a fascinating tenant and ally, not as a treatment method. If you find on the floor something that looks like a miniature scorpion, do not kill it, leave it in peace, because you have in the hive one of the few natural enemies of varroa.

How to read it so it makes sense

A few rules that make the difference between looking and seeing.

First, compare. A single image of the floor says little. Only setting several colonies side by side, and the same colony over time, shows what is the norm and what is a departure. So it is worth looking regularly and building yourself a reference point.

Second, the floor is a signal, not a diagnosis. The mess on the floor tells you where to look, not exactly what is going on. Treat it as a clue that directs an attentive nest inspection, not as a verdict. Ejected brood or many corpses is an invitation to look deeper, not a ready answer.

Third, combine with the rest. The varroa drop, the state of the brood, colony strength, smell, moisture, all of it forms a picture only together. A solid floor is valuable precisely because it gathers many of these signals in one place, but only your head assembles them into a whole.

This is where the advantage lies of a beekeeper who knows what is going on in their hives over one who merely looks in. The floor is not a bin to empty. It is a daily report the colony issues about itself, for free, if only you learn to read it.

Curiosities and controversies

A miniature scorpion that eats varroa lives in the hive. The book scorpion, Chelifer cancroides, is a tiny arachnid related to scorpions, recorded in hives as a beneficial predator for over a hundred years. Molecular studies confirmed it eats varroa, and under camera it picks out mites and leaves the brood alone. The trouble is that it has all but evaporated from modern, smooth, chemically treated hives, so today it is more a fascinating puzzle and a research direction than a ready weapon.

A chewed mite is a note from the breeder. If you find on the tray mites with legs torn off and a damaged shell, it is a trace of grooming, that is the bees cleaning themselves. It is one of the resistance traits, so the floor can point you straight to colonies worth breeding from. Few people look at it that way, and it is a free breeding hint lying on the tray.

The drop betrays brood rearing before you open the hive. Researchers can estimate the area of brood in a colony by counting and weighing the cappings and larval faeces falling to the floor, because their quantity tracks the colony's development. You do not have to do it to the centimetre, but the principle is the same: a sudden shower of cappings speaks of intense brood emergence, and its disappearance of the queen easing off, all without breaking the nest apart.

In winter an open floor divides beekeepers. A mesh floor works great for monitoring and in summer, but in winter the dispute returns: some leave it open for ventilation and dryness, others close it, citing research on the huge heat losses of a thin-walled hive. It is the same insulation versus ventilation war as with wintering, only seen from below, and there is no single right answer for every hive.

A mesh floor can lie about moisture. A screened floor lets out not only mites but also part of the signals about the nest's state. A wet, mouldy tray on a solid floor screams about poor ventilation, while through the mesh the same problem can slip by. The convenience of the varroa measurement is thus paid for with a loss of other information, and that is a real argument for keeping at least some colonies on solid floors.

Most common mistakes

Treating the floor like a bin. Tipping the tray out without a look is throwing away a free report on the colony. Look first, clean second.

Reading one colony in isolation. Without comparison to others and to the same colony over time you will not tell the norm from a problem. Floor diagnosis is a game of comparisons.

Confusing a signal with a diagnosis. Ejected brood or corpses on the floor call for a deeper look, they do not settle on their own what is going on. The floor directs the inspection, it does not replace it.

Ignoring mould and moisture. A wet, mouldy floor is not cosmetics, but a warning of poor ventilation that costs colonies in winter.

Killing beneficial tenants. Before you sweep off the floor something that looks like an odd bug, take a look. A miniature scorpion is a book scorpion, an ally against varroa, not a pest.

Forgetting the correction for a solid floor. The raw varroa drop from a solid floor is understated, because part of the mites are cleared away. For counting infestation use a tray and a more reliable method, such as an alcohol wash or EasyCheck.

Sources and further reading

• Read S. et al. (2015). Ingestion of Varroa destructor by pseudoscorpions in honey bee hives confirmed by PCR analysis. Journal of Apicultural Research 54(5). Molecular confirmation that book scorpions eat varroa in hives.

• Donovan B. J., Paul F. (2005). Pseudoscorpions: the forgotten beneficials inside beehives. Bee World. A review of a century of observations of book scorpions as hive predators.

• Work on estimating brood area from the drop of cappings and larval faeces. Background for reading colony development from the floor.

• Mitchell D. (2023). Honeybee cluster, not insulation but stressful heat sink. Journal of the Royal Society Interface. Context for the open-floor debate in winter.