The Lives of Bees
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labeled bees away from the two sugar- water feeders that lay at the heart
of my experiment.
This experiment began when my assistants and I trained 10 bees to col-
lect sugar water from each of two feeders located north and south of the
study colony’s hive. Both were 400 meters (0.25 miles) from the hive.
During this training period, both feeders were filled with a dilute (30
percent) sugar solution that was attractive enough to motivate the bees
visiting each feeder to continue foraging from it but was not rich enough
to stimulate them to recruit hive mates to it. The critical observations
began at 7:30 on the morning of June 19, which followed a 10- day period
of cool, rainy weather, during which the bees could not leave their hive.
We loaded the north and south feeders with 30 percent and 65 percent
sucrose solutions, respectively, and began recording the number of differ-
ent individuals visiting each feeder. By noon, the colony had generated a
strong pattern of differential exploitation of the two foraging sites: 91 bees
were bringing home food from the richer feeder to the south, but only 12
bees were doing so from the poorer one to the north (Fig. 8.9). We then
swapped the positions of the richer and poorer feeders for the afternoon,
and by four o’clock the colony had switched the primary focus of its forag-
ing from south to north. The colony’s ability to choose between forage
sites was again demonstrated the following day in a second trial of the
experiment. Thus, we saw that when we gave our study colony choices
between two food sources that differed in profitability, the colony consis-
tently focused its collection efforts on the more profitable site. The net
result was that the colony steadily tracked the richest foraging site within
a changing array. Perhaps the most impressive feature of these experimen-
tal results is the high speed of the colony’s tracking response. Within four
hours of the noon reversal of the positions of richer and poorer sites, the
colony had completely reversed the distribution of its foragers. These re-
sults show us that wild colonies are highly skilled at coping with the dy-
namics in foraging opportunities that they experience in the wild, such as
those that Kirk Visscher and I detected when we spied on the waggle
dances performed inside a colony living in the Arnot Forest.
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North feeder
South feeder
8 AM
1
0
30%
65%
Noon
12
91
65%
25%
4 PM
121
10
Fig. 8.9. Diagram showing the ability of a colony to choose between two foraging
sites (sugar- water feeders) with 30 percent and 65 percent sucrose solutions. The
number of dots above each feeder denotes the number of different bees that
visited the feeder in the 30- minute period preceding the time shown on the left
(8:00 a.m., Noon, 4:00 p.m.) on 19 June. For several days prior to the start of
the experiment, a small group of bees was trained to go to each feeder (12 bees
to the north feeder and 15 to the south); thus on the morning of 19 June the two
feeders had essentially equivalent histories of low- level exploitation by the study
colony. The two feeders were located 400 meters (0.25 mile) from the hive and
were identical except for the concentration of the sugar solution.
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HONEY ROBBING IN THE WILD
Beekeepers have long known that honey robbing can be severe among
colonies in their apiaries, but until recently nothing was known about the
importance of robbing among colonies in the wild. We can be sure that in
both settings the bees have a powerful incentive to steal. A pound of honey
is about 80 percent sugar, whereas a pound of nectar is (on average) only
about 40 percent sugar. These numbers tell us that when a worker bee flies
home with her crop stuffed with stolen honey, she brings home twice as
much energy for the colony than if she were returning with her crop filled
with nectar. Furthermore, a crop filled with honey can be far less costly to
obtain than one filled with nectar; a honey robber visits just one spot to
load up (see below) whereas a nectar forager typically visits dozens, if not
hundreds, of flowers to gather a full load. A robber, however, risks being
killed by defenders of the honey she tries to steal. But if this risk is low, as
it is when the colony being robbed is weak or even dead, then the energetic
advantages of robbing honey relative to collecting nectar strongly favor
theft.
Robbing is a fascinating part of the biology of honey bees given its sig-
nificance as a form of intra specific kleptoparasitism, or parasitism by theft
(usually of food). I suggest, though, that the primary significance of rob-
bing lies in its potential to promote inter specific parasitism by fostering the
transmission of parasites and pathogens between colonies. For example, if
a colony is robbed while it is dying from an infestation of Varroa mites and
associated viruses, then the robbers are likely to become infested with
these mites and carry them home. Robbers can also carry home certain
pathogens from dead colonies, including the highly virulent spores of Pae-
nibacillus larvae (American foulbrood) and the less dangerous spores of
Ascosphaera apis (chalkbrood). To understand the importance of robbing in
spreading parasites and pathogens between colonies, we need to know
how long these agents of disease can survive in dying and dead colonies,
and how quickly such colonies are found by robbers. Previous studies of
robbing have focused on robbing in the artificial situation of colonies living
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Food Collection 211
crowded in apiaries, so until recently, the importance of robbing among
colonies living dispersed in the wild remained unknown.
To begin to fill this gap in our knowledge of the natural history of Apis
mellifera, one of my PhD students, David T. Peck, and I investigated how
rapidly unguarded honey is discovered by robbers in two settings: wild
colonies in the Arnot Forest and managed colonies in my five apiaries at
Cornell. As was explained in chapter 2, the colonies in the Arnot Forest
have a density of 1 colony per square kilometer, so in this setting the aver-
age distance to a colony’s nearest neighbor is about 1 kilometer (0.6
miles). The colonies in my apiaries are arranged in pairs on hive stands, so
here a colony’s nearest neighbor is less than 1 meter (ca. 3 feet) away. We
provided unguarded honey in these two scenarios (forest and apiary) by
putting out “robbing test boxes” (RTBs), which were made by cutting old
Langstroth hive bodies in half and adding a wall, a floor, and a lid. The
entrance opening of each RTB was a hole 2.5 ce
ntimeters (1 inch) in di-
ameter drilled into one end. We equipped each RTB with one frame of
capped honey and three frames of dark, aromatic comb. The most reveal-
ing trial of this experiment was conducted in October 2015, when frosts
had eliminated most of the flowers so the bees were keen to find colonies
to rob. We set out simultaneously 10 RTBs in the Arnot Forest and 10
RTBs in my apiaries near Ithaca, about 25 kilometers (15 miles) from the
Arnot Forest. We deployed the 10 RTBs assigned to the forest by hanging
them from tree limbs to make them safe from black bears (see Fig. 2.15).
We also spaced these boxes approximately 1 kilometer (0.6 mile) apart,
to mimic the spacing of the nests of wild colonies. We deployed the 10
RTBs assigned to the five apiaries in two ways: either suspended from the
limb of a tree (as in the Arnot Forest) near the apiary or set atop a cement
block within the apiary.
The results for our experiment are shown in Figure 8.10. Every robbing
test box that was hung near or placed within an apiary was discovered by
the end of the first day of good weather. Every robbing test box hung in
the Arnot Forest was robbed too, but these boxes were discovered more
slowly. It took 10 days of good weather for the robbers to find them all.
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10
8
6
4
Apiary
2
Forest
Number of boxes robbed
0
2
4
6
8
10
Foraging days
Fig. 8.10. Records of discovery of robbing test boxes in Arnot Forest and in
apiaries, 8 October to 12 November 2015. Time scale is foraging days, i.e., days
in which weather conditions were good enough for foragers to make flights.
Thus, we found that in an apiary setting, during a nectar dearth, every box
containing unguarded honey was discovered rapidly by robbers. This result
was expected. What was not expected, however, was the test result that
all the boxes dispersed in the Arnot Forest were also discovered, though
relatively slowly. It may be that our test boxes are more conspicuous, and
thus are more easily found by robbers, than natural nest cavities. Never-
theless, the complete success of robber bees in discovering our test boxes
in both scenarios suggests that even in the wild, where dying (or dead)
colonies must be relatively hard for robbers to find, there are opportuni-
ties for parasites and pathogens to be transmitted between colonies by
robbers bringing home the honey stores of colonies weakened (or killed)
by disease.
By chance, David Peck and I also managed to watch closely the behavior
of robber bees while they were loading up on honey inside an unoccupied
hive. This happened in early July 2017, after I noticed bees robbing from a
bait hive that I keep on the sloping roof of a shed attached to my barn at
home. A swarm had moved into this hive in June 2016, but it had died
during the winter of 2016–2017. In early May 2017, I opened the hive to
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clean out the dead bees, and in doing so I found that the hive contained
two frames still nearly full of honey. I left them in place thinking that they
might help attract another swarm. When I came home from work on 30
June 2017, I was excited to see bees zipping in and out of this hive. Were
they scouts from a swarm checking it out? With a ladder, I climbed to the
hive and gently removed its cover to have a look inside. What I saw was
robbers loading up on honey. Cool! This opportunity to watch robbers
plunder another colony’s nest was too good to pass up, so I had to do
something that would allow me to watch them closely. Soon I was back
with a two- frame observation hive, which I set on sawhorses arranged
inside the shed. I transferred from the bait hive to the observation hive the
two frames of honey- filled comb, and then I hid the bait hive. Almost im-
mediately, the robbers were investigating the observation hive.
For the next two days, David Peck and I watched the robbers at work
inside the observation hive. We noticed that, as a rule, a robber bee does
not uncap a honey cell to have a personal honey source. Instead, she walks
across dozens or hundreds of capped honey cells and eventually joins a
knot of fellow robbers extracting honey from one of a handful of already
opened cells. We also saw that if a robber does open a capped cell of honey,
she cuts with her mandibles just a pinprick- size hole in the cell’s capping.
This opening is just large enough to admit her tongue. In time, it will be
enlarged by other bees that join her in drinking from “her” cell. This econ-
omy of the robber bees in uncapping honey cells means that they spend
most of their time inside the robbed nest standing head- to- head, some-
times pushing each other back and forth slightly, but usually standing sur-
prisingly still. We timed several robber bees from entry to exit and found
that on average they spent 12 minutes in the hive. Seeing these bees stand-
ing nearly motionless, and crowded around a few partially uncapped cells,
revealed to us that when robbers invade a dying colony they provide Varroa
mites with excellent opportunities to climb onto them. One prior study
has shown that Varroa mites are extraordinarily nimble creatures; they can
climb onto a feeding worker bee, via a leg or her tongue, in the blink of
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an eye. Another study has shown experimentally that when Varroa mites
find themselves in highly infested colonies they no longer avoid foragers
when they scramble onto worker bees.
It is now clear from studies of the ability of robbers to find dead or
dying colonies, together with our little study of the behavior of robbers
inside a dead or dying colony’s nest, that robbing by honey bees gives Var-
roa mites excellent opportunities for moving from a dying colony to a
healthy colony, even where colonies are widely spaced across a landscape.
Fifteen years ago, I was deeply surprised to find that Varroa mites had
managed to infest the entire population of wild colonies in the Arnot For-
est. But now, knowing how skilled robber bees are at finding the nests of
dead and dying colonies, and knowing how robbing bees stand nearly
motionless for several minutes when loading up on honey inside the nests
of these colonies, I will be surprised to ever find a wild colony without
Varroa mites.
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9
TEMPERATURE CONTROL
No warmth, no cheerfulness, no healthful ease,
No comfortable feel in any member—
No shade, no shine, no butterflies, no bees,
No fruits, no flowers, no leaves, no birds,
November!
—Thomas Hood, “November,” 1844
Thomas Hood’s poem, written in London in 1844, expresses well the
isolation that we can feel when winter sets in and nature goes quiet. No
butterflies, no bees. On these days, though, we can take heart from know-
ing that the bees are merely out of sight, not gone. Inside a bee hive or bee
tree, there are still thousands of active bees, huddling and shivering, creat-
ing a warm refuge that is well stocked with heating fuel—their honey
stores. In this regard the honey bee is unique, for it is the only insect living
in seasonally cold climates that creates year- round a cozy microclimate in
which it stays active. From late autumn to midwinter, the time when honey
bee colonies are without brood, the temperature of the bees clustered
inside a hollow tree or man- made hive stays well above freezing. The core
temperature of a broodless winter cluster rarely falls below 18°C (64°F),
and the temperature of its mantle—its outermost layer—usually stays
above 7°C (44°F), even when the ambient temperature is −20°C (−4°F) or
colder. Then from late winter to early autumn, the stretch of time when
colonies are rearing brood, the temperature in the nursery region of a
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honey bee colony’s nest is maintained between 34.5°C and 35.5°C (94°–
96°F), varying by less than 0.5°C (1°F) across a day, even if the temperature
outside drops below 0°C (32°F) in late winter or it soars above 40°C
(104°F) on the hottest days of summer.
Another measure of the remarkable thermal stability of the nursery
region of a honey bee colony’s nest is the high sensitivity of honey bee
brood to small deviations from the normal, 34.5°–35.5°C temperature
range of the broodnest. When Jürgen Tautz and colleagues reared capped
brood—pupae and late- stage larvae—in incubators set to 32°C, 34.5°C,
and 36°C (90°F, 94°F, and 97°F), labeled the young bees upon emergence
with paint marks, and then introduced them to a foster colony living in an
observation hive, they found clear differences in behavior among the
temperature- treated bees when they foraged from a sugar- water feeder
300 meters (980 feet) from the hive. On average, a bee raised at 32°C
performed only 10 circuits of the waggle dance upon return to the hive,
whereas those raised at 34.5° or 36°C performed 50 circuits. Also, the
waggle dances performed by the 32°C- reared bees indicated the feeder’s