Although the numerical abilities of many vertebrate species have been investigated in the scientific literature, there are few convincing accounts of invertebrate numerical competence. Honeybees, Apis mellifera, by virtue of their other impressive cognitive feats, are a prime candidate for investigations of this nature. We therefore used the well-established delayed match-to-sample paradigm, to test the limits of honeybees' ability to match two visual patterns solely on the basis of the shared number of elements in the two patterns. Using a y-maze, we found that bees can not only differentiate between patterns containing two and three elements, but can also use this prior knowledge to differentiate three from four, without any additional training. However, bees trained on the two versus three task could not distinguish between higher numbers, such as four versus five, four versus six, or five versus six. Control experiments confirmed that the bees were not using cues such as the colour of the exact configuration of the visual elements, the combined area or edge length of the elements, or illusory contours formed by the elements. To our knowledge, this is the first report of number-based visual generalisation by an invertebrate.

Recent studies have shown that honeybees flying through short, narrow tunnels with visually textured walls perform waggle dances that indicate a much greater flight distance than that actually flown. These studies suggest that the bee's “odometer” is driven by the optic flow (image motion) that is experienced during flight. One might therefore expect that, when bees fly to a food source through a varying outdoor landscape, their waggle dances would depend upon the nature of the terrain experienced en route. We trained honeybees to visit feeders positioned along two routes, each 580 m long. One route was exclusively over land. The other was initially over land, then over water and, finally, again over land. Flight over water resulted in a significantly flatter slope of the waggle-duration versus distance regression, compared to flight over land. The mean visual contrast of the scenes was significantly greater over land than over water. The results reveal that, in outdoor flight, the honeybee's odometer does not run at a constant rate; rather, the rate depends upon the properties of the terrain. The bee's perception of distance flown is therefore not absolute, but scene-dependent. These findings raise important and interesting questions about how these animals navigate reliably.

When a scout honeybee discovers an attractive patch of flowers, she performs the famous 'waggle dance' that advertises the location of the food source to her nestmates (von Frisch, 1993). The dance consists of a series of alternating lefthand and right-hand loops, interspersed by a segment in which the bee waggles her abdomen from side to side. The duration of this 'waggle phase' conveys to the potential recruits the distance of the food source from the hive: the longer the duration of the waggle, the greater the distance (von Frisch, 1993). This information is used by the recruited bees to locate the food source. Clearly, then, the scout, as well as the recruits, is able to gauge how far she has flown in search of food.Early studies concluded that bees estimate distance flown by gauging the amount of energy they expend to reach the destination (for a review, see von Frisch, 1993). More recent studies, however, are providing increasing evidence that this 'energy hypothesis' is incorrect, at least for moderate distances of a few hundred meters (Neese, 1988;Esch et al., 1994Esch et al., , 2001Esch and Burns, 1995;Srinivasan et al., 1996Srinivasan et al., , 1997Srinivasan et al., , 2000. Over these distances, bees appear to gauge distance flown in terms of the extent to which the image of the environment moves in the eye Burns, 1995, 1996;Srinivasan et al., 1996Srinivasan et al., , 1997Srinivasan et al., , 2000Esch et al., 2001). In other words, the optic flow experienced by the eye (that is, the speed of motion of the image of the environment) is integrated over time to obtain an estimate of distance traveled. The most compelling evidence for this was obtained in a study in which bees were trained to fly to a feeder placed inside a short, narrow tunnel, the walls and floor of which were lined with a random visual texture. When bees returned to the hive from the tunnel, they performed a waggle dance in which they indicated a feeder distance as large as 200 m, despite the fact that they had only flown a distance of 6 m (Srinivasan et al., 2000). Evidently, the proximity of the walls and floor of the tunnel greatly amplified the magnitude of the optic flow that they experienced, in comparison with the situation during outdoor flight in a natural environment. On the other hand, when the same tunnel was lined with axial stripes -so that a bee flying through it would experience very little optic flow, because the stripes were parallel to the flight direction -the bees signaled a very small distance, even though they had flown the same physical distance as in the previous condition (Srinivasan et al., 2000). This experiment indicated that distance flown was being measured in terms of integrated optic flow, and not in terms of physical distance flown or energy consumed.If bees do indeed gauge distance traveled by measuring optic flow and integrating it over time, it is pertinent to enquire into the properties of their visually driven 'odometer'. Given that the environment through which a bee flies can vary substantially ...

The robustness and plasticity of working memory were investigated in honey bees by using a delayed matching-to-sample (DMTS) paradigm. The findings are summarized as follows: first, performance in the DMTS task decreases as the duration between the presentation of the sample stimulus and the presentation of the comparison stimuli is increased. This decrease is well approximated by an exponential decay function. Performance is significantly better than random-choice level even at delays as long as 5 sec and is reduced to random-choice levels at an average delay time of 8.68 ؎ 0.06 sec. Second, when the DMTS task involves two samples (one relevant, the other irrelevant), bees can be trained to learn to use the relevant sample to perform the task if (i) the relevant sample is always at a fixed position, or (ii) the relevant sample always has the same place in the sequence of presentation (always first or always second). Bees that have learned to use the relevant sample and to ignore the irrelevant sample can generalize this learning, and apply it to novel sets of sample and comparison stimuli that they have never previously encountered. The findings point to a remarkably robust, and yet plastic, working memory in the honey bee.honey bee learning ͉ matching-to-sample ͉ maze ͉ tunnel

The ability to perceive the number of objects has been known to exist in vertebrates for a few decades, but recent behavioral investigations have demonstrated that several invertebrate species can also be placed on the continuum of numerical abilities shared with birds, mammals, and reptiles. In this review article, we present the main experimental studies that have examined the ability of insects to use numerical information. These studies have made use of a wide range of methodologies, and for this reason it is striking that a common finding is the inability of the tested animals to discriminate numerical quantities greater than four. Furthermore, the finding that bees can not only transfer learnt numerical discrimination to novel objects, but also to novel numerosities, is strongly suggestive of a true, albeit limited, ability to count. Later in the review, we evaluate the available evidence to narrow down the possible mechanisms that the animals might be using to solve the number-based experimental tasks presented to them. We conclude by suggesting avenues of further research that take into account variables such as the animals’ age and experience, as well as complementary cognitive systems such as attention and the time sense.