Introduction:

BEEKEEPING IN THE NORTHEAST - An account of my beekeeping, not a treatise of expertise, but for friends & family who wish to keep bees vicariously through me, and for the occasional apiarist passer-by.

Tuesday, October 29, 2019

Long, Mild Autumns in the Northeast… Why Fall Has Been My Bees' Most Dangerous Time of Year


How many bees are needed to maintain optimal temperatures over winter?
This is very hard to estimate for the beekeeper. It varies by length of
confinement and regional temperatures that also vary.
We are learning new facts about bees all the time but this information from past published research on honey bees has served me well. Corrections always welcome:
  
3 Important Autumn Temperatures in Northern New England:

#1 - AIR TEMPERATURE OUTSIDE OF HIVE:

  • 64°F: honey bees begin to cluster to keep the queen and themselves warm
  • Nighttime temps: 45-57°F - worker bees cast out drones to protect food reserves
  • 57°F: honey bee family cluster becomes more compact
  • 45°F: Guards may be disabled. Predator insects like wasps are free to assault the hive until the first or second killing frost
  • 23°F  bees generate warmth inside by vibrating their thorax in the cluster
#2 - INDIVIDUAL BEE TEMPERATURE:
  • 57°F: Too cold to fly from a still start, or “Coma” threshold, however when muscles are “warmed up” can fly in colder temperatures and will try to forage. This can result in great losses in population when as many as 2/3 of a colony's adult bees go out as foragers, flying farther to find food in a barren landscape during short daylight hours with dropping temperatures.
  • In clustering temperatures "Heater bees" crawl inside of empty cells, vibrating their thorax muscles to keep the surrounding cells warm. Empty cells serve a purpose.
  • One single heater bee is thought to have the ability to keep up to 70 adjoining cells warm.
#3 - CLUSTER TEMPERATURE
  • 95°F: optimal core temperature.
  • 81°F: average temperature inside of a cluster.
  • 48°F: average temperature exterior shell of cluster.
  • 100°F: highest recorded temperature of a cluster.
How much honey to leave? 60 to 120, depending
on the colony, is my practice.
Thoughts: Mild outside temperatures in autumn + no forage = robbing behaviors and/or dwindling populations when foragers fly farther to find food in a barren landscape during short daylight hours with dropping temperatures. 

The death of honey bee foragers from cold and mowing practices in the country often leads to failed clustering efforts. This sets colonies up for attack from the high wasp populations - and with low native insect populations becoming the norm, wasps are all the more a threat. (For mowing impacts on colony loss see "Apimondia Istanbul - Promoting Bee Friendly Farming Methods - Walter Haefeker".

In my experience, bees protecting brood may not break clusters to protect food reserves from being robbed. Once the adult population has dwindled out the nurse bees stand little if any chance of compensating for their loss or surviving into winter. Often all that is left of a cluster after such events are the queen and a few attendants. To read more on this pheromone driven phenomenon: See Randy Oliver's "Old Bees, Cold Bees, No Bees" Part 1 and Part II."

What can the beekeeper do?
  • Monitor fall colony populations and food reserves. In cold weather this means paying attention to outside activity. Some beekeepers weigh their hives before & after a flow. Research ways to use a scale without being intrusive:
    • Northern healthy honey bees generally consume 10-12 pounds of food a month. 
    • Error on the side of southern honey bee appetites and leave or help your bees create 15 to 20 lbs of food per month for overwintering colonies.
  • Monitor wasp activity. Destroy nests when necessary. Pollinator gardens may help. I seem to be discovering that a garden attracting a diverse pollinator population all season long, near my colonies, results in animals that prey on wasps and wasps not so intent on assaulting my hives.
Ideal temperature-driven behaviors when the nectar and pollen flow are over:
Thermal imaging is great,
but don't rely on these images alone.
Know your colonies.
  • The colony population should be sufficient enough to maintain a core temperature of 95°F with an outer layer of population maintaining a temperature of 48°F. If you can take a peak with a thermal camera, fine, but rely on your familiarity with the colony. When in doubt, and we always are, research combining and overwintering strategies for small clusters.
  • “heater bees” vibrate thorax muscles to raise body temperature 16° higher than normal 111°F. Bees along the outer shell of the cluster remain motionless, conserving energy and acting as a layer of insulation. Don't let motionless fool you into assuming they are dead. Many hives have been dismantled into the snow and cold that may have otherwise survived if the beekeeper only understood the girls' talents and dedication to colony survival.
  • Warmer bees (95F) from the inside of the cluster, tucked into comb cells, continually change places with the colder bees (48°F) along the outer edge of the cluster to allow the colder bees, who have been eating, to warm up and “burn” off respiration. So the girls do not necessarily have their little legs crossed all winter waiting to void. See this very dry but fascinating YouTube from the UK's National Honey Show: Ben Harden.
Thank you for caring enough about your bees to spend time reading such information as your fellow beekeepers can share in blogs. Despite the abundance of information on the web, it has always been the tradition of beekeepers to teach this craft by carefully sharing what they think they've learned when interacting with, and especially keeping alive in our climate, these brilliant and ancient, productive animals.

1 comment:

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