Everyone knows that honey bees regulate the temperature and humidity to optimum levels for the hive the entire year-round.
I was just curious, how do they maintain constant hive temperature and humidity throughout the wide fluctuations between hot summer days and cold winter nights?
I began digging for answers and this is what I discovered:
How do honey bees regulate temperature and humidity in the hive?
Honey bees regulate hive temperature using bee muscle activity and clustering to heat the hive.
Cooling is accomplished with wing flapping and water mist evaporation.
Humidity is controlled with air circulation and droplets physically removed.
Honey bees have two reasons to control the beehive temperature:
- Keep the newly developing larvae and pupae warm and alive.
- Keeping the Queen bee warm enough to survive the cold of winter.
These two activities are totally separate.
Heating the hive to warm the newly developing brood takes place during the the spring build up of brood in the hive as it prepares to send hoards of new bees into the fields to collect the nectar offered up by the blooming flowers.
It takes the average worker bee 21 days to metamorphosis from egg to emerging adult worker bee.
The Queen bee will start her egg laying activity again just after the winter solstice. She will need to have those eggs developed and ready to forage by the time of the first nectar flow of the year.
The first nectar flow of the year, the spring nectar flow, starts with the earliest blooming trees in your area. The Queen must have worker bees ready to go get the pollen and nectar as soon as it appears.
Trees in bloom can appear as early as January in some areas. That is why the Queen begins laying eggs just after the winter solstice on December 21st.
Egg laying reaches its peak at the summer solstice on June 21st. This is when the bulk of flowering plants have completed the production of nectar and pollen production and the hive’s need for more workers diminishes until the start of the fall nectar flow.
As long as pollen is coming into the hive the Queen will continue to lay eggs. The number of eggs laid will depend on the amount of pollen available to be collected. If the Queen overproduces eggs for the amount of pollen coming into the hive to feed the larvae, the nurse bees either underfeed the larvae or simply eat the excessive eggs before they become larva.
Honey bees, unlike humans, think of seasons by the amount of daylight hours, not be the ambient temperature outside the hive. They start to ramp up activity when the days get longer and start to shut down for that long winter’s nap as the days get shorter and pollen is in short supply to collect.
When the winter solstice is past, the bees begin to concentrate on warming the newly developing bee larvae instead of concentration on keeping the Queen alive exclusively.
The bees keep the internal temperature of the beehive at a constant temperature of between 90 to 95 degrees Fahrenheit day and night, 365 days a year.
Heating the Developing Bee Pupae
Within the beehive there are bees that are identified as “Heater” bees.
Heater bees disengage the rear portion of their 4 wings to perform their role as a heater bee. The rear portion of the wings need to be interlocked to achieve flight.
With the rear wing disconnected, the heater bee begins to contract and relax the muscles used for flight. They work these muscles so vigorously that they raise their body temperature to about 110 degrees Fahrenheit.
Once the heater bee has reached the optimum body temperature, they climb into an empty cell next to the developing pupae to keep the pupae warm. The heater bee can regulate the temperature of up to about 70 pupae.
When the queen is laying eggs, she will leave empty cells which will be designated as “heater bee cells”. They are strategically placed throughout the brood to maximize the effects of heater bees.
Sometimes the heater bee will be seen on top of the brood cell. When they are heating the pupae in this fashion, they will be seen pressing their abdomen against the top of the birth cell.
Developing honey bee pupae are kept at an optimal temperature of between 95 degrees and 97 degrees Fahrenheit. Some say this temperature variance is intentional, and the specific temperature an individual pupae is kept at, affects the “kind” of honeybee that will emerge.
In addition to heater bees, the nurse bees will cover the top of the capped brood to help keep the pupae warm. The entire brood will be covered with nurse bees, so much so that it will be difficult to see the capped brood below their bodies.
It requires, at minimum, one nurse bee to cover three capped pupae cells to keep the pupae warm, but normally there are many more covering the capped brood area.
An adult honey bee keeps their body temperature at 95 degrees Fahrenheit. When the outside ambient air drops to 50 degrees Fahrenheit or lower the honeybee can no longer maintain a 95 degree body temperature and that is why they usually do not fly if the temperature is below 50 degrees Fahrenheit.
Some claim honeybees can not fly in temperatures at 50 degrees or less, but this is disputed by many beekeepers seeing their honey bees flying in temperatures much below 50 degrees.
Some beekeepers are in the habit or putting their ear to the hive sidewall during the winter months listening for buzzing to determine if the bees are surviving their over-wintering posture.
If they hear no buzzing at all, they will “knock” on the side of the hive, which will excite the bees enough that the beekeeper can hear the buzzing, a sign the hive is still alive. They also report that “knocking” on the side of the hive has occasionally produced a mass of several hundred bees to fly out of the hive to see if they need to attack. These bees are certainly flying in temperatures well below 50 degrees Fahrenheit.
Bees also fly in temperatures below 50 degrees Fahrenheit to do “cleansing runs”. Honeybees can “hold it” for extreme amounts of time when they are inactive. But is a slightly warm day presents itself you may well see honeybees exiting the hive on a cleaning run.
So to recap:
- Worker bee eggs are ignored for three days until
thedevelop into larvae.
- Cells of the new larva are then filled with Royal Jelly, optimally for 6 days, then capped by wax. Once capped, the larva is now a
- After 12 days in the wax capped brood birthing cell, the pupae emerge as a fully functioning adult honeybee.
this 18days as uncapped and capped larvae and pupae, they need to have their body temperature regulated by heater and nurse bees.
Keeping the Queen Alive Over Winter
Honey bees are cold blooded. They must stay warm to be able to even move. They keep their body temperature up through muscular activity. If their body temperature drops too low they are essentially paralysed and cannot generate heat with muscle activity.
The Queen bee must be kept at between 80 degrees and 95 degrees Fahrenheit all winter long, day and night, or she will die and come spring all the bees in the hive will be dead, frozen to death. In cold periods of time the bee cluster will allow the center of the cluster, where the queen is, to drop to about 81 degrees fahrenheit to conserve energy.
The outside of the bee cluster can have temperatures drop to as low as 48 degrees Fahrenheit. The outer bees in the cluster migrate into and out of the center of the cluster to maintain their own body temperature.
In the overwintering cluster of bees cannot keep the cluster warm, they will freeze to death.
This is called a “dead out”.
Even the most seasoned of the beekeepers will experience dead-outs!
When a beekeeper opens the hive in January and all the bees are dead, it is usually because the bees did not have enough honey store reserves to make it through the winter.
Bees do not really ever freeze to death, they starve to death and then become frozen.
Beehives require between 40 and 75 pounds of stored honey to successfully overwinter, dependant on the local climate.
Without enough honey reserves to eat, the bees cannot generate heat using muscle activity. If they cannot generate heat with muscle activity they will freeze to death, but in reality, they really starved to death.
Hives without enough stored honey to make it through the winter will need to be fed by the beekeeper to be able to make it through the winter.
However, feeding the bees in late fall can cause confusion within the hive about the true nature of the environment, and can fool them into believing there is still nectar being gathered from flowers in bloom.
This confusion within the hive may cause the Queen to delay laying new “winter bees”. New winter bees are needed to have the hive emerge on the other side of winter in good shape.
A hive overwintering with old summer bees instead of new winter bees sets the hive up for complete collapse in about March, even though they seemed to have overwintered successfully.
Many different factors can cause a beehive to enter the winter with old “summer bees”. Beehives that enter the winter with old summer bees will seem to over-winter just fine but suffer hive collapse in March when the nectar flow is really kicking into high gear.
Usually this hive will still have adequate supply of honey stores in the brood box at the end of winter. The beekeeper is in a quandary, not knowing why the hive just simply collapsed.
The cause of this situation, according to seasoned beekeepers, is the fact that the hive went into winter with old summer bees instead of newly born “winter bees”.
The old summer bees just simply run out of life in about March, leaving the hive without enough foraging bees to bring in the pollen necessary to raise brood. The hive just collapses. This is usually a very fast process. A hive appearing healthy in late February or early Mach can be completely wiped out in a couple weeks.
So, seasoned beekeepers frequently adopt the philosophy of requeening every fall to insure the hive will go into winter with a strong force of winter bees that will not die out of old age in March of the new year. The new Queen will lay eggs that will develop into winter bees with the strength and genetics to come out of winter with a lot of life and is able to forage for the vast amounts of pollen necessary to raise the new workforce of foraging bees from the very active new Queen bee laying a large number of new eggs.
Seasoned beekeepers claim that requeening in the fall produces a much stronger, more healthy spring hive that grow and produce at a much higher rate than a hive that has over-wintered with an old Queen.
Annual requeening is usually done in July, August, or September so the new Queen will be laying strongly going into the winter as well as coming out of winter.
Marginal hives that are not going to be requeened in the fall are frequently combined to make the hive stronger with a better chance of surviving the winter, but even these combined hive do not do as well as the requeened hive.
Humidity is the ability of air to hold moisture. The higher the air temperature, the more water it can hold. Humidity and air temperature are proportionally related.
In general, the ideal humidity in a strong bee hive rearing young is between 50% to 60%.
The dilemma is the humidity needs within the hive vary depending on the activity being performed.
Decreased Humidity Needs
For honey to “cure”, the humidity needs to be low, the bees are trying to get the water content of the finished capped honey at below 20%. Over 20% water content is considered as unacceptable.
The lower the water content of the honey, the more valuable that honey is to most honey connoisseur.
Honey containing to much water tends to ferment, causing it to be undesirable.
Nectar coming into the hive for processing into honey has a water content of 80% to 95%.
Increased Humidity Needs
During periods when the hive is raising brood, the brood area will have a higher humidity level than the remainder of the hive, primarily because of the presence of the liquid contained in Royal Jelly, the substance all larvae are bathed in during uncapped development of larvae into capped pupae.
If the humidity is below 50% in the brood cells, no eggs will hatch into larvae, and eggs are ignored by nurse bees until the egg metamorphosis into a larvae, about three days after being laid by the Queen.
The increased humidity in the brood area can/will change the humidity level in the entire hive.
The humidity within the beehive during non brood rearing times is relative to the hive temperature. The higher the temperature the more the humidity. The hive is not being affected by the fluids in Royal Jelly because the hive is not raising larvae.
So the health of the hive can be determined, in part, by hive humidity. In brood rearing times the hive humidity will be stable, but in periods of non-brood rearing, the hive humidity will fluctuate with the temperature inside the hive.
Bee’s Techniques for Moisture Control
The honey bees control excessive hive humidity with wing-fanning for air circulation and cooling, removing droplets of condensation with their tongues, and even building “reservoirs” to hold the excessive fluids until they can remove the water.
Beekeeper Techniques for Moisture Control
Many beekeepers feel excessive hive moisture in the hive is the biggest risk factor for a hive dying overwinter. The beekeeper can help the bees by making sure the hive is adequately ventilated (especially if the beekeeper is using a solid bottom board).
Adding a moisture board can help the bees control hive moisture a lot.
Many also use a rear shim tilting the hive forward about 3 degrees to allow condensation drops to run out of the hive naturally.
Interesting Side Effect of Humidity
Varroa mites do not do well in high humidity!
Paying It Forward
What is a beehive dead out?
A “dead out” is when a beekeeper opens a beehive for the first time after overwintering, and all the bees are dead. The hive did not survive the winter.
Dead outs need to be cleaned up as soon as possible to prevent the hive structure being destroyed by wax moths.