Drought and Honey Bees

Entomology News and Information:
Drought and Honey Bees

Top: Honey bees cool the hive by “bearding,” which makes more room within the hive and increases air circulation. 

Bottom: This hive is being attacked by honey bees from another hive, who are attempting to rob it of its honey. Even if the resident bees successfully fend off the attack, many bees will be killed.

Most of Utah has experienced severe to extreme drought conditions this year. It is easy to understand the direct effects that hot weather and water scarcity have on our crops and other plants. However, we don’t often think of the effects of drought on bees and the resultant impacts on our plants, not only now, but in the future. Drought stresses bees in many, often intertwined, ways that we don’t consider.

Just like other animals, bees are very dependent on water for drinking. Also like other animals, bees’ food sources are water dependent. When water is scarce, plants produce less nectar and pollen, and therefore bees have less food. In the case of honey bees, not only are bees unable to meet the hive’s current demand for food, but they are unable to store an adequate supply of honey to get them through the winter. For an unmanaged colony, this means starvation. To sustain managed colonies, beekeepers can feed them in the fall to provide adequate winter stores, but this can become expensive, especially when beekeepers may have already lost income by not having a marketable honey crop.

A beehive should have at least 25 pounds of honey going into winter. If the colony is large or if the winter weather is particularly cold or particularly warm, the hive will need even more honey. At minimum, beekeepers attempting to boost winter food stores will feed their hives sugar syrup. Each hive is different, but my most recent personal experience was that a first year hive required about 25 pounds of sugar per week for 4 weeks during September and October, in order to build up enough food storage to get them through until April, when I supplemented with sugar syrup again while waiting for plants to produce adequate nectar.

Sugar syrup isn’t nearly as nutritious as nectar, so beekeepers will often add essential oils to the sugar syrup, which are believed to add nutritive value and boost bees’ immunity to diseases and parasites. Additionally, in mid to late winter, bee colonies will begin to gradually increase their populations, which requires sufficient pollen stores. If the beekeeper feels that the bees were unable to store enough pollen for this purpose, bees are often fed a pollen substitute beginning in late winter or early spring.

Drought’s effect on bees’ ability to get adequate food and water may seem obvious, but it also influences their ability to maintain hive temperature, which should ideally be around 95?F for developing brood. If it gets too hot inside of the hive, the first step the bees take will be to increase air circulation by increasing space within the hive. Many of the bees will move outside and cling to the outer surface of the hive, which is called bearding.

During extremely hot weather when bearding isn’t enough, bees evaporatively cool the hive by bringing in drops of water and fanning them with their wings. Bees will also align themselves and fan at the hive entrance. If the hive is consistently overheated and water for cooling is hard to come by, foragers will cease searching for nectar and pollen and instead focus on finding water. Extreme heat can dry out bee brood, so it makes more sense to keep them cool and moist than it does to find food for larvae that may not survive anyway. Temperature maintenance, as you can see, becomes a particular challenge because high heat requires water for cooling, just when water resources are especially scarce.

Another less obvious consequence of drought is the need for bees to increase their defenses. As resources become ever scarcer, bees from other hives, as well as wasps, become desperate and will begin robbing weaker hives of their honey. Wasps will even steal brood. A hive can be completely “robbed out” in just a few days. As a result, bees are forced to devote time and energy to hive defense rather than foraging for food and water.

Drought stresses honey bees in a variety of ways, including food and water shortages, temperature regulation challenges, and an increased need for hive defense. All of these factors are correlated, and falling short in any of these areas can result in the death of the hive either immediately or over the winter. Therefore, the drought we have experienced this year could impact our plants next year if bee populations are reduced enough to result in a pollinator shortage. Although we can’t control the weather, we can take steps to conserve pollinators, thus lessening the blow in years that the weather proves to be a challenge. It is important to consider not just honey bees, but all pollinators, in our pest management plans and in our day to day activities. The Xerces Society is an excellent source for more information.

-Cory Stanley, USU CAPS Coordinator& Bee Specialist