The Lives of Bees

by Thomas D Seeley

  This is the nest- site variable that I investigated most closely in my studies

  of nest- site selection by honey bees living in the wild around Ithaca, and it

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  is the one that has most strongly attracted further studies by other biolo-

  gists in North America. I began by setting up 14 test arrays, each of which

  consisted of four cubical nest boxes of different sizes: 10, 40, 70, and 100

  liters (ca. 2.6, 10.6, 18.5, and 26.4 gallons). Over the next two months,

  I found that no swarms had occupied the 10- liter boxes, but that 11 swarms

  had moved into the larger boxes. This told me that 10 liters is too small

  for the bees. To see whether there is a size that is too large for them, I cre-

  ated 10 more test arrays that consisted of paired nest boxes of just two

  sizes, 40 and 100 liters. Now I found a striking pattern: seven swarms

  occupied the 40- liter boxes, and none moved into the 100- liter ones.

  Given these results, I concluded that swarms in my study area strictly avoid

  10- liter cavities (too small) and strongly prefer a 40- liter cavity to a 100-

  liter one (too large). I did not explore further the upper limit of acceptably

  sized nest cavities for wild colonies in the Ithaca area, but I did investigate

  further the bees’ lower limit for an acceptably sized nest cavity. In tests

  where wild swarms could choose between 10- and 25- liter (2.6- and

  6.6- gallon) nest boxes, or between 17.5- and 25- liter (4.6- and 6.6- gallon)

  ones, I found they readily occupied the 25- liter nest boxes but never the

  10- liter ones and almost never the 17.5- liter ones. This makes sense, be-

  cause a 10- liter, and even a 17.5- liter nesting cavity—which has only about

  40 percent of the volume of a deep Langstroth hive body—is too small to

  hold the ca. 20 kilograms (44 pounds) of honey that a colony living in the

  Ithaca area will consume over winter.

  I reported my findings in 1977, and soon afterward two investigators at

  the University of Illinois, Elbert R. Jaycox and Stephen G. Parise, reported

  their studies that showed that artificial swarms of yellow- bodied Italian

  honey bees ( A. m. ligustica) avoided 5.2- liter (1.4- gallon) cavities, but ac-

  cepted 13.3- and 24.4- liter (3.5- and 6.4- gallon) ones, and that swarms

  of black- bodied Carniolan honey bees ( A. m. carnica) rejected 5.2- and

  13.3- liter cavities, but accepted ones with volumes of 24.4, 43.5, and 85.1

  liters (6.4, 11.5, and 22.5 gallons). Their findings indicate that honey bees

  of different geographic races have different lower limits for an acceptably

  sized nest cavity, and that bees of races native to colder regions (e.g., the

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  Carniolan bees, native to the Carnic Alps, between Austria and Italy) re-

  quire bigger cavities, probably to hold larger stores of honey.

  The idea that the bees’ nest- site preferences are adaptively tuned to

  their native climate is reinforced by a large- scale study conducted in 1981

  by Thomas E. Rinderer and colleagues at the USDA’s Honey Bee Breeding,

  Genetics, and Physiology Research Laboratory in Baton Rouge, Louisiana.

  They studied nest- site selection as a function of cavity size by wild swarms

  of European honey bees around Baton Rouge. To do so, they erected 10

  wooden platforms 3 meters (ca. 10 feet) off the ground, and on each plat-

  form they set six nest boxes: two each of 5, 10, and 20 liters (1.3, 2.6, and

  5.3 gallons); or two each of 20, 40, and 80 liters (5.3, 10.6, and 21.1

  gallons); or two each of 40, 80, and 120 liters (10.6, 21.1, and 31.7 gal-

  lons). This team found that swarms occupied mainly the 20- or 40- liter

  boxes, and rejected the very small (5- liter) and very large (80- and 120-

  liter) boxes.

  One more study, conducted by Justin O. Schmidt in the late 1980s and

  early 1990s, compared the nest- site preferences of European and African-

  ized honey bees with respect to cavity volume. This investigation focused

  on determining the minimal size of an acceptable homesite. It found that

  when wild swarms of European honey bees living in Arizona, and also wild

  swarms of Africanized bees living in Costa Rica, were given a choice be-

  tween artificial nest cavities (pulpwood pots) with volumes of 13.5 or 31.0

  liters (3.6 or 8.2 gallons), the swarms of both types of honey bee would

  occupy cavities providing only 13.5 liters of nesting space. It also found,

  however, that the European bees (but not the Africanized bees) occupied

  preferentially the pulpwood pots that provided a 31.0- liter nest cavity.

  The acceptance of 13.5- liter cavities by some of the swarms of Euro-

  pean honey bees living in Arizona surprised me at first, but then I real-

  ized that this result suggests that these bees have become locally

  adapted—that is, have experienced changes in the genes controlling

  their nest- site preferences—to living in this place without harsh winters.

  Although wild colonies of European honey bees living in central New

  York cannot survive winters living in 13.5- liter nesting cavities, evi-

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  dently wild colonies of these bees can do so in southern Arizona, and this

  may have relaxed selection pressure on these bees to avoid occupying

  such small living quarters.

  Combs in Cavity

  This variable was tested by setting out 12 pairs of 40- liter (10.6- gallon)

  nest boxes. One box in each pair contained a 300- square- centimeter

  (46- square- inch) slab of dark, old beeswax comb propped against one

  wall, while the other box contained no comb. Four of these 12 pairs of

  nest boxes attracted a swarm: three moved into the box with the comb,

  one into the box without the comb. This suggested that the bees do prefer

  a cavity that comes furnished with some comb. Also, when I inspected the

  box with comb at the site where the swarm had occupied the box without

  comb, I found that it contained a large colony of yellow jacket wasps ( Vesp-

  ula germanica), one powerful enough to repel me! This meant that the box

  with comb at this site had not been available to the honey bees. All in all,

  I had three clear choices of the comb- containing box over the empty box.

  Not a definitive result. Nevertheless, I believe that it is likely that bees

  strongly prefer sites that are already equipped with combs.

  Tibor I. Szabo, working in Alberta, Canada, reported that swarms in-

  stalled in hives containing a full set of combs produced nearly twice as

  much honey across a summer compared to swarms placed in empty hives:

  81 and 43 kilograms (178 and 95 pounds), respectively. There is also the

  fact that tree beekeepers in medieval Russia valued much more highly tree

  cavities that had been occupied by bees compared to those that had not.

  Nest- site Properties Not Important to Bees

  I thought that bees might prefer a nest entrance that is tall and thin over

  one that has the same area but is circular, because the former might be

  more easily defended. The wild swarms, however, showed no
preference

  in this nest- site property. They also showed no preference for a box whose

  floor was covered with 2 liters (0.5 gallons) of dry sawdust relative to

  one in which the floor covering was soggy sawdust. Furthermore, the wild

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  swarms showed no preference for a box with solid walls relative to one

  whose front and side walls were each perforated with 25 holes, each one

  6.35 millimeters (0.25 inch) in diameter.

  The bees’ lack of choosiness about cavity dryness and draftiness puzzled

  me until I took down the occupied boxes and opened them to transfer the

  swarm bees inside to standard hives. I was surprised to find that the bees

  living in the boxes with the sawdust- covered floors had tidily removed this

  loose stuff, both the dry and wet forms. I also was surprised to find that

  the bees that had occupied the drafty boxes had plugged all the holes in

  their walls with propolis. Suddenly, it all made sense: honey bees are not

  choosy about nest- site details that they can fix after moving in. Of course,

  they cannot modify things like the entrance height or cavity size, so they

  must get these things right by carefully choosing their homesites.

  What I found most surprising, however, was the absence of a preference

  for a tall box (interior dimensions 100 centimeters tall by 20 centimeters

  wide and deep/39.4 inches tall by 7.9 inches wide and deep) relative to a

  cubical box with the same volume. I knew that out in the woods, which is

  their natural habitat, the bees live in tree hollows that are usually tall and

  rather narrow. I also knew that they arrange the contents of their nests

  with a conspicuous vertical segregation of the honey (stored above) and

  the brood (reared below). Therefore, I strongly expected them to prefer

  cavities in which their combs would have a large vertical dimension, but

  when I studied the variable of cavity shape by putting out 12 pairs of nest

  boxes, with one tall box and one cubical box in each pair, I found no sign

  of a preference. Nine of the 12 pairs of nest boxes attracted a swarm: three

  moved into the tall box, six into the cubical box. Evidently, the bees do

  not have a strong preference for tall nest cavities.

  COMB BUILDING

  Finding a snug nest cavity is just the first of several hurdles that a wild

  colony of honey bees must clear if it is to survive its first year. Its next

  challenge is building the beeswax combs whose cells will provide the

  fledgling colony with cradles for its brood and cupboards for its food (Fig.

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  Fig. 5.8. Comb in the brood nest showing cells containing eggs, larvae, and

  pollen.

  5.8). This construction work begins without delay, because without combs

  the new colony can neither begin rearing the worker bees it needs to bol-

  ster its strength nor start stockpiling the honey it needs to survive the

  coming winter. It is not surprising, therefore, that many of the bees in a

  swarm have scales of fresh beeswax protruding from the ventral surface of

  their abdomens (Fig. 5.9), an unmistakable sign that these bees are primed

  for comb building. Another indicator of the pressing need for plentiful wax

  in fledgling colonies is the remarkably broad age range of the swarm bees

  with fully functional wax glands. It is not just the middle- aged worker

  bees—the ones that are usually the primary wax producers in a colony—

  but also the older worker bees. Normally, these elderly bees are engaged

  in foraging and have nothing to do with making wax and so possess degen-

  erate wax glands, but when they are members of a swarm they rejuvenate

  their wax glands and so help fill their colony’s critical need for beeswax.

  Indeed, the thickness of the wax- gland epithelium—a measure of a bee’s

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  Fig. 5.9. White beeswax scales protruding from the four pairs of wax glands on

  the underside of a worker bee’s abdomen.

  rate of wax production—is the same for the middle- aged bees and the

  elderly bees in a swarm.

  The energetic cost of synthesizing the wax needed to build a complete

  nest is huge. We have seen already that a typical nest of a wild colony con-

  sists of several curtains of beeswax comb whose total area is about 1.2

  square meters (ca. 12.9 square feet). Each of these combs is double- sided,

  so the total surface area is approximately 2.4 square meters (ca. 25.8

  square feet). Approximately 80 percent of the surface area of these combs

  consists of the smaller worker cells (about 82,000 total) and the other 20

  percent consists of the larger drone cells (about 13,000 total). To build this

  immense structure, a colony’s worker bees must produce some 1.2 kilo-

  grams (2.6 pounds) of beeswax, which represents the lifetime wax pro-

  duction of approximately 60,000 worker bees, or about five times the

  population of the swarm that founds a colony. On average, a worker bee

  in a swarm contains about 35 milligrams (0.001 ounce) of a 65 percent

  sugar solution, so collectively the 12,000 bees in a typical swarm carry an

  energy supply of some 275 grams (0.6 pounds) of sugar. Given that the

  weight- to- weight efficiency of beeswax synthesis from sugar is at most

  about 0.20, and that one gram of wax yields about 20 square centimeters

  (ca. 3 square inches) of comb surface, the complete conversion of an aver-

  age swarm’s sugar supply into comb will produce about 1,100 square

  centimeters (1.2 square feet) of comb surface—less than 5 percent of the

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  comb in a completed nest. The other 95 percent of the nest’s construction

  must be funded by the income of the colony’s nectar collectors over the

  following months and years.

  The cost of nest building can also be reckoned in comparison to the

  energy consumed by a colony over winter. Knowing that honey is an ap-

  proximately 80 percent sugar solution, and knowing that bees have ap-

  proximately 20 percent efficiency in converting energy into wax, we can

  calculate that producing the 1.2 kilograms (2.6 pounds) of wax in a typical

  nest requires expending the energy contained in some 7.5 kilograms (16.5

  pounds) of honey. This much honey (as we will see in the next chapter) is

  about one-third of the honey consumed by a colony over a winter to fuel

  its heat production. Clearly, the cost of nest construction is a major item

  in a colony’s energy budget during its first year, which means that colonies

  can benefit greatly from energy conservation during nest building. In fact,

  a colony’s very survival may depend on such frugality. We will see in chap-

  ter 7 that only about 20 percent of the incipient (founder) colonies living

  in the woods around Ithaca survive to the following spring. Most perish in

  winter when they exhaust their honey stores.

  Nest building starts as soon as the swarm bees have moved into their

  chosen tree hollow. The work begins with some of the bees
chewing off

  the loose, crumbly punkwood from the cavity’s ceiling and upper walls.

  Soon other bees begin coating the cleaned surfaces with tree resins (prop-

  olis). This site- preparation work is partly a long- term investment in nest

  hygiene (see below), but initially it functions mainly to create smooth,

  hard, varnished surfaces to which the soon- to- be- built combs will be at-

  tached. Meanwhile, most of the bees in the swarm assemble themselves

  into a mass of linked chains of bees suspended from the ceiling and walls

  of the cavity. For the next several days, nearly all the bees in the colony—

  except some foragers and water collectors—will hang essentially motion-

  less in the dark interior of their new home, all the while secreting tiny

  scales of wax from glands on the underside of their abdomens (Fig. 5.9).

  The comb construction commences when individuals with well-

  developed wax scales disconnect themselves from their sisters, climb

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  upward through the hanging braids of bees, and deposit their wax on the

  cavity’s ceiling or walls. To remove a wax scale from one of the wax- gland

  pockets on the underside of her abdomen, a bee presses a hind leg firmly

  against the ventral surface of her abdomen and then slides it rearward until

  one or more of the larger spines in the leg’s pollen comb skewers a scale

  and dislodges it from its wax- gland pocket. Next, the hind leg bearing the

  scale is drawn toward the head, where the wax scale can be grasped by the

  forelegs and chewed by the mandibles. The scale is chewed to mix it with

  a mandibular gland secretion that makes it more plastic, then it is depos-

  ited on the surface where the comb building is getting started or is already

  underway. Initially, these wax deposits produce just small piles of wax, but

  eventually the piles merge into a ridge of wax several millimeters (ca. 0.25

  inch) long. At this point, the sculpting of cells begins. First, a cavity the

  width of a worker cell is excavated in one side of the wax ridge, and the

  excess wax is deposited along the sides of the hole. This work is repeated

  on the other side of the ridge of wax, but here two cells are dug, such that

  the center of the first cell on one side is between the two cells on the other