I am getting so many questions about feeding syrup to winter bees that I decided to re-run this post from last year. Two points are especially important. First, it is the temperature of the syrup—not the temperature of the outside air—that governs whether the bees will drink the syrup. If you are having nights in the 30s or 40s, even if the daytime air spikes into the 60s, the syrup will not be warm enough. Sugar syrup has a high heat capacity, in other words it takes a lot of heat to warm it up.
Second, a container of syrup in your hive in cold weather will not harm the bees, but neither will it help them. The bees will just ignore it. But it is a waste of syrup, it will probably get moldy, and it can add moisture to a hive you are trying to keep dry. So why go there? Just give your winter bees fondant, hard candy, or granulated sugar instead.
So here’s the original post. I’ve added some related posts at the end. I particularly recommend “Physics for beekeepers: why bees can eat solid sugar in winter.”
Q: What should I feed my bees, sugar syrup, fondant, or hard candy?
A: Both liquid feed and solid feed have their place. Ideally, a solution of 2:1 syrup can be fed in the fall until the syrup itself reaches about 50°F (10°C). In colder temperatures solid feed (either fondant or hard candy) should be fed.
Q: I’ve heard that evaporating the syrup is particularly difficult for the bees in cold weather and this is why it shouldn’t be fed in winter. What do you think?
A: There are really two questions here.
Q1: Is it difficult for bees to evaporate water from syrup in winter?
A1: Absolutely. Cold air can hold less moisture than warm air, so in a cold hive no amount of fanning will evaporate the water from cold syrup. Think of dew. Dew forms on objects because the cold air of evening cannot hold all the moisture that warmer daytime air can hold. As the temperature drops, the water vapor literally falls out of the air and condenses on things. If winter air cannot hold the moisture from the syrup, it will not evaporate no matter how hard the bees work.
Q2: Is this why you shouldn’t feed syrup in winter?
A2: Most winter feed is not given to bees in the hopes they will store it, it is given to bees to keep them from starving should they run out of honey. A feeder full of cold syrup in your hive will not hurt your bees, but it won’t help them either. It just sits there because it is too cold for the bees to drink. And since they won’t drink it, it is not an emergency food source.
Q: Don’t bees need some water in order to eat hard candy and fondant?
A: Yes, a source of moisture is needed, but there is plenty of moisture in the hive for this. The moisture from bee respiration condenses on cool surfaces just like the dew. Since the fondant or candy is above the bees, the moisture from their respiration lands on it and condenses. Unless you live in the desert, damp air coming in from outside through the entrance may condense on the solid sugar as well. These sources provide plenty of water for the bees to consume solid sugar.
Q: Won’t bees leave the hive in dangerously cold temperatures in order to find water to dilute the fondant?
A: No. Bees don’t commit suicide. At any rate, the colder the air, the less water it will hold—and the more bee respiration will condense on the sugar.
Q: I’m confused. I thought 2:1 syrup was fed to bees in order to build up reserves for winter.
A: It is. But, as I mentioned above, the purpose of fall feed and the purpose of winter feed are different. A hearty feeding of 2:1 syrup in the fall while temperatures are still warm enough to evaporate it will be stored by the bees and used to increase their winter food supply. On the other hand, the purpose of winter feed is to keep bees that are low on stores from starving—they are not going to store their winter feed, they’re going to eat it.
Q: Should all bees be fed sugar?
A: No. Bees should eat honey. Sugar is fed when a colony hasn’t collected sufficient stores to make it until spring, when the beekeeper has over-harvested, or when the beekeeper needs to administer certain medicines, such as Fumagilin for Nosema diseases.
Q: So you’re not advocating solid sugar over liquid sugar?
A: I’m not advocating anything. I’m just trying to explain why the bees treat different feeds differently at different temperatures. Very specific physical properties govern how the world works. The more you know of these, the easier it is to make good management decisions.