Uninvited guests: who gets into the hive in autumn and how to stop them

When the colony is strong and alert in summer, guards patrol the entrance and every intruder gets a slap before it enters. But in autumn everything changes. The bees dwindle, grow sluggish with the cold, come out less and less, and the cluster begins to tighten. And exactly when the colony loses its vigilance, a queue of guests forms at the hive, seeing in it either a free larder, or a warm billet for the winter, or both. A few minutes of work in September and October save colonies that would otherwise die not of frost but of a lodger.

Below is a practical review of autumn intruders: who really does harm, who only frightens, and what to do with each. Without panic, but without complacency either, because some of these guests can take a colony apart in a week.

Mouse and shrew: the quiet destroyers number one

Let us start with the biggest real threat, because it is not the hornet from the headlines but small mammals. In autumn, when the bees pack into a cluster and stop defending the entrance, a mouse walks calmly inside. There it finds warmth, shelter and free food: it eats the store, chews the combs, crunches dead and torpid bees, and makes a bed from the nest material. By spring it can wreck several combs and turn the bottom box into a stinking nest, while the colony, stressed by the rodent's presence, winters wretchedly. In a polystyrene or polyurethane hive the damage can be worse still, because a mouse easily gnaws corridors and chambers in the soft wall, making itself a snug nest in the hive's insulation, and such a hole you cannot patch, you have to replace the part.

The worst of it is that a mouse does not need much. It squeezes through an opening the size of a finger, so a wide-open entrance is a gateway for it. The solution is dead simple and cheap: narrowing the entrance and a mouse guard, that is a strip with holes small enough that a bee passes but a mouse does not. Timing is key. You fit the guard before the colony packs into a cluster and stops defending the entrance, that is in late autumn at the first cold. If you are late and the mouse is already inside, merely fitting the guard shuts it in the hive, which is even worse. Then you flush it out first, and only then secure the entrance. From my own experience the best solution is a rodent mesh nailed or clipped over the whole entrance: the mesh lets a bee through but stops a mouse, and along the way it defends the entrance against other intruders, because a bigger insect such as a hornet cannot get in through it either.

Wasps and robbing: when the enemy has wings

Late summer and early autumn are the peak of wasp activity. When the flows in nature end, wasps look for sugar wherever they can, and a hive full of honey is target number one. A weakened, small colony can be literally robbed of its store by wasps, losing its own bees in the fight at the entrance along the way.

Here the ally is again a narrowed entrance. A small entrance is a short line of defence that a handful of guards can hold, whereas a wide-open one they cannot. On top of that, keep the apiary tidy: do not leave spilled syrup, scraps of wax or cappings out in the open, because that invites wasps and cranks up robbing. Incidentally, the same rule guards against robbing by other bees, because in autumn your own bees from strong colonies will just as gladly rob a weaker neighbour. Narrowed entrances and no sugar in sight are the best insurance. It also works well to set out wasp and hornet traps around the apiary, for instance bottles with a fermenting, sweet bait, which catch the insects before they get to the hives and thin their numbers in the area. And if you have a mesh or rodent guard on the entrance, that same barrier keeps hornets out, because they cannot force their way through it into the hive.

Worth adding that the native European hornet, the big one everyone fears, does hunt single bees under the hive, but for a strong colony that is an acceptable loss and usually does no real harm. There is no point exterminating it, because it is a useful predator and the losses to a healthy colony are marginal.

The Asian hornet: a threat on its way

And here we come to the guest that clicks in the headlines, so let us deal with it properly. The Asian hornet, Vespa velutina, also called the yellow-legged hornet, is an invasive species that came to Europe from Asia early this century and steadily pushes east, at roughly a hundred kilometres a year. Do not confuse it with Vespa mandarinia, the giant hornet from the sensational clips under the label murder hornet, that is a different, larger species.

The state today is this: in Poland the Asian hornet has not yet been officially recorded, but it is already in the Czech Republic, Slovakia and Germany, so beekeepers say plainly it is a matter of time. Why is it dangerous, unlike our European hornet? Because it hunts differently. It hovers in the air in front of the entrance and snatches returning, laden bees, and does so in groups and persistently. A colony besieged by hornets stops flying out, falls into paralysis from hunger and stress and weakens. A single hornet colony can catch an enormous number of insects in a season.

What to do about it now, before it appears? Above all learn to recognise it: it is smaller than our hornet, dark, almost black, with a single orange band on the abdomen and characteristic yellow leg tips, hence the name yellow-legged. If you see such an insect or a large, papery nest high in a tree crown, do not try to remove it yourself, but report it, because eradication only makes sense if the first foci are caught. The earlier someone spots the first individuals, the greater the chance of stopping it. This is a topic in which beekeepers will be the first line of defence, so it is worth keeping your eyes open. In the meantime the same things help as against wasps and the native hornet: a narrowed, meshed entrance the predator cannot enter, and traps catching the hunting individuals by the apiary.

The woodpecker and other birds: a winter problem few think about

In winter, when insects are scarce, the woodpecker becomes an unexpected nuisance. Hearing the hum of the cluster inside the hive, it gets to work: it hammers through the wall or the entrance to get at the bees, and into the hole it makes come frost, damp and the other intruders. For a woodpecker a wintering hive is a larder full of protein it only has to drill into.

And it is not only the woodpecker. Tits and other birds will perch on the entrance, tap at the wall and pick off bees coming out one by one, luring them out into the frost, so in winter birds can be a real nuisance. You do not have to fight them, just make access harder, and what works best is bird netting stretched over the hive or in front of the entrance, so the bird has nothing to brace against or perch on. Instead of netting, loosely hung cloth or bubble wrap is used, the point being that the beak has no purchase. In areas where birds are a nuisance, it is a simple step that saves a lot of nerves and hammered walls.

Marten, badger and bear: the heavier calibre

Finally the animals that do not squeeze through the entrance but take the hive by force. Here the scale of damage is different, because we are talking about toppled, smashed hives and colonies lost in a single night.

Marten. Agile, curious and strong for its size, it can take an interest in a hive, especially if it stands within a leap from a tree or a roof. It rarely smashes a wooden hive, but a polystyrene or polyurethane one it can claw and gnaw apart, getting inside through the soft wall. Besides, it plunders, pulls out what it can through the gaps, throws off roofs and constantly disturbs the colony with nightly visits. Martens prowl around buildings and lofts, so an apiary near the farmstead can be on their route. How to protect yourself: set the hives stably and strap the boxes with clips or straps, weight or bolt down the roofs so it cannot throw them off, and move the hives away from trees, walls and roofs the marten jumps from. Polystyrene hives in marten country are worth additionally shielding, for instance boarding or meshing the vulnerable spots so there is nothing for it to gnaw.

Badger. A more serious opponent, because the badger is strong, stubborn and greedy for both brood and honey. It can topple a poorly set hive, break the floor or wrench off the entrance to get inside, and once it has found an easy source of protein and sugar, it comes back night after night. Honestly: I do not know a sure, one-hundred-percent method against a badger, because it is a powerful, stubborn animal. How to protect yourself so as to make its work as hard as possible: set the hives on a solid, raised stand they are fixed to, so they cannot be easily toppled or pulled to the ground where the badger takes them apart. And in areas where badgers really roam, the surest barrier is a fence around the apiary, best under current, the same as against a bear.

Bear. In the mountains and the east of the country this is a real and the most dangerous threat of all, because a bear can smash a whole apiary in one night, treating it like a buffet. For it, toppling a hive and tearing out the brood and honey is the work of a moment. Here there are no half measures, and here the method is clear: the only truly effective protection is a proper electric fence of adequate power, correctly set around the whole apiary. No weight of hive, no stand or casing will stop a bear, only a shocking, well-earthed fence. On top of that, in bear country, a sensible choice of site away from their trails.

The common denominator with larger animals is one: stability, location and a barrier. A hive set firmly, on a solid stand, strapped or weighted, is harder to topple. An apiary away from dense scrub and animal trails is less of a temptation. And where badgers or bears roam, no weight of hive will replace a fence under current.

How to protect yourself, in short

All these threats share one thing: they strike the colony when it is weakest and least alert. So defence comes down to a few simple, cheap moves made in time.

Narrow the entrances, and it pays off twice, because a shorter line lets the bees defend against wasps and robbing, and you against mice. Fit a mouse guard or rodent mesh over the entrance before the colony packs into a cluster, but make sure no one is already inside, and aim for a finer mesh, because a shrew squeezes through where a mouse gets stuck, and the same mesh keeps hornets out. Set out wasp and hornet traps around the apiary. Keep it tidy, with no spilled sugar or wax in sight. Set the hives stably, strapped, on a solid stand and away from dense scrub, and where badgers or bears roam, put up an electric fence, because the weight of the hive will not stop them. Learn to recognise the Asian hornet and report it rather than fight alone. And if you live where woodpeckers and other birds are a nuisance, cover the hives with netting for winter.

All of this is a quarter-hour of work at the hive, and the difference in spring can be that between a strong colony on its cleansing flight and a wrecked, mouldy nest with a mouse inside.

Curiosities and controversies

The Asian hornet versus the murder hornet. The media notoriously confuse two species. Vespa velutina, the one heading for Poland, is smaller than our native hornet. Vespa mandarinia, the giant hornet of the sensational headlines, is a completely different, much larger species from Asia, not present in Europe. Whoever mixes the two usually spreads panic instead of knowledge.

The native hornet is an ally, not an enemy. The European hornet inspires dread by its size, but for a strong colony it is practically harmless, and useful at that, because it hunts flies and other insects. Destroying its nests is a common mistake born of ignorance. The real problem is only its Asian cousin.

A mouse does more harm than many a predator. Though the headlines frighten with hornets and bears, it is the unremarkable mouse that wrecks more colonies in Poland each year than exotic threats. A quiet, cheap-to-stop intruder that is easy to underestimate and that can ruin the wintering.

A shrew is not a mouse, and a guard will not stop it. Though people lump them together, the shrew is not a rodent but an insectivore more closely related to the mole than to the mouse. It is one of the smallest mammals in Poland, so it slips through gaps smaller than a typical mouse guard allows. On top of that it does not hibernate in winter but hunts nonstop, because its metabolism is so fast that it eats its own body weight a day. In the hive it goes not for the store but for the torpid bees.

A strong colony defends itself. Most of these intruders are opportunists that strike at weakness. A strong, populous colony with a narrowed entrance will fend off wasps, robbing and mice practically without your help. Again the same truth from the whole series returns: the best defence is a healthy, strong colony, not another gadget.

Most common mistakes

A mouse guard fitted too late. You fit it when the mouse is already inside, and shut it in with the store. The guard goes on the entrance before the colony packs into a cluster.

A wide entrance into late autumn. An open entrance is an invitation to wasps, robbers and mice at once. Narrow it as the colony weakens.

Sugar and wax in sight. Spilled syrup, cappings and scraps of wax in the apiary crank up robbing and draw wasps. Keep things tidy, especially in autumn.

Exterminating the native hornet. The European hornet does no real harm to a strong colony and is useful. Destroying its nests is shooting yourself in the foot.

Panic instead of observation with the Asian hornet. Instead of spreading alarm, learn to recognise it and report the first sightings. Early detection is the only moment when anything can be done.

Sources and further reading

• Materials on the biology and spread of the Asian hornet Vespa velutina in Europe, including publications by portals and agricultural advisory centres from 2025. Basis for the description of the threat and the current state.

• Textbook recommendations on protecting hives for winter against rodents and other intruders. Basis of the practical part.

• Accounts distinguishing Vespa velutina from Vespa mandarinia and from the native Vespa crabro. Background for species recognition.