The Waggle Dance of Bees - A Symptom, Not a Signal? We have had a lively exchange this past couple of months on BEE-L about how recruited bees find a new source of food or how swarms manage to move to a new location. The swarm relocation problem allows us to assess the relative credibility of the odor-search and bee language hypotheses. As we all know, when a swarm issues from a hive it most often clusters on a nearby object (e.g., tree, bush). Experienced foragers inspect potential nest cavities, return to the swarm cluster, and execute waggle dances. Eventually, the swarm takes flight and travels to only one of the prospective sites. Consider first an odor-search model. Scout bee activity actually occurs not only on the swarm cluster but also is quite frenzied at each potential nest cavity. Those of us fortunate to have watched that behavior at a potential destination know that scouts repeatedly expose their Nasanov glands, both inside and outside those cavities. Some of them also execute waggle dances on flat surfaces near cavity entrances. How does the swarm eventually manage to move to only one of those cavities instead of splitting, with some portion going to each of the sites? An explanation that relies solely on odor is very simple. With experienced bees flying back and forth between cluster and likely sites, one of those sites becomes easier to locate for other recruited bees from the swarm cluster. They, then, also expose their Nasanov glands at such a site. That odor, drifting downwind, provides a "beacon" for newly recruited bees. Searching bees can execute a zigzag flight upwind once they get within the downwind odor plume. In time, the easiest of the sites to find has many more bees exposing their glands at that site than at the other sites, etc. ("positive feedback"). Eventually, the less favored sites get no new recruits at all and are abandoned. When many bees frequent a single site, and weather permits, all scout bees from that site return to the cluster, the swarm cluster disbands, and the swarm is led through the air by the few hundred bees who know the way. The experienced travellers do so by opening their Nasanov glands as they repeatedly fly out ahead of the swirling bees in flight. One can find a partial description of this process in the following article: Wenner, A.M. 1992. "Swarm movement: A mystery explained." AMERICAN BEE JOURNAL. 132 (1):27-31. James Cowan, a perceptive beekeeper in Aberdeen, Washington, later provided additional information in his letter to me of 13 January 1992, as well as in his letter on page 819 in the last November issue of ABJ and in another letter to me this month. How much did research and writing of that article cost beekeepers? Nothing. ********* Consider now the bee language explanation for the same event. In his posting of January 15th, Peter Borst emphasized "decision making" by dancing bees on the swarm cluster and included the following comment from one of the publications (*3) that he referenced: ********* "The main focus of the article is on how a decision is made as to which site a swarm will go to among the several choices located by the scouts. The way in which the bees communicate information about the site is as follows:" 'Scout bees fly throughout the surrounding countryside, searching for new nest-site cavities. When a scout returns after inspecting a high-quality cavity, she performs waggle dances which encode the distance and direction to the site. Most bees that danced for nest sites also followed the dances of other scouts.' The method of communicating information is similar to that used by foraging bees to recruit more foragers to a productive site." ********* On February 1st, he expanded on the theme of "animal consciousness," a belief system embraced by Donald Griffin (ANIMAL THINKING) and also by Richard Dawkins in his popular works. Can scout bees "build consensus" on the surface of the swarm cluster? Some folks think so, as in a recent publications by a group at Cornell: "Group decision making in swarms of honey bees" (1999. BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY. 45:19-31). In the authors' words, it was a "...study that renews the analysis of honey bee swarms as decision-making units." Their interpretation of what happens among scout bees on the swarm cluster (in part): "...in consensus building ... bees that dance initially for a non-chosen site [tend] to cease their dancing altogether, not to switch their dancing to the chosen site..... even though a swarm is composed of tiny-brained bees it is able to use the additive weighted strategy of decision making because it distributes among many bees the task of evaluating numerous potential sites and the task of selecting one particular site for its new home." ********* Nowhere in that publication could I find any mention of the very visible Nasanov gland exposure at the prospective cavities, even though they wrote: "Once the scouts have completed their deliberations, they stimulate the other members of the swarm to launch into flight and then steer them to the chosen site (...Michener 1974; Seeley 1982; Winston 1987)" Nor could I find any mention of the wind direction that prevailed during their experiments. Why did they not mention my 1992 article that appeared in the AMERICAN BEE JOURNAL (an article that includes much of the information at the beginning of this posting)? I strongly suspect it was because they do not want to draw attention to any element that does not fit with their favored hypothesis, the notion of bee language. ********* My overall interpretation of all of the above? Swarm movement depends on Nasanov odor produced by scout bees. That odor drifts downwind from suitable cavities and also enables scout bees to lead swarms through the air to the new site. The dance maneuvers on the surface of the swarm clusters and at the new site are thus merely a SYMPTOM (not a cause) of what is happening during swarm relocation. Julian O'Dea hinted as much when he termed the dance "idiothetic behaviour" in this extended exchange --- as Rosin did recently in the AMERICAN BEE JOURNAL (p. 98 in the February issue). Bee language proponents thus concentrate too much on a study of the symptom (i.e., waggle dance), rather than on the total event of swarm movement. They ask us to believe that a group of scout bees can form a consensus on the surface of the swarm cluster, when a simple Nasanov (and odor-search) explanation for swarm movement is sufficient. Having made the comparison, we can ask: Which is the more credible hypothesis? And how much did the complicated research on "decision making" cost the public? We cannot know for sure, but that Cornell research was supported by grants from both the National Science Foundation and the U.S. Department of Agriculture. Did taxpayers get their money's worth? That is for all of us to decide. Swarming season is upon us. Hopefully, some of you may find time to repeat James Cowans' careful observations (as covered in his November letter and in his letters to me directly). Adrian Adrian M. Wenner (805) 963-8508 (home phone) 967 Garcia Road (805) 893-8062 (UCSB FAX) Santa Barbara, CA 93106 ******************************************************************** * * "When we meet a fact which contradicts a prevailing theory, * we must accept that fact and abandon the theory, even when * the theory is supported by great names and generally * accepted." * * Claude Bernard --- 1865 ********************************************************************