Humans often define themselves in terms of how they are different from other forms of life on this planet, particularly with respect to cognitive ability. We often don't realize how similar we are to other critters.
This similarity goes beyond the well-known examples of chimpanzees and apes. Dogs have a sense of justice, dolphins have a sense of numbers, and a parasitic wasp has even been shown to learn.
Many scientists continue to investigate the extent to which cognitive abilities are found in mammals. Fewer corresponding studies have been performed with insects.
Scientists led by Jürgen Tautz (University of Würzburg, Germany) and Shaowu Zhang (Australian National University) have addressed this gap in our knowledge. They have shown that honeybees have a sense of numbers, similarly to many mammals.
Why study honeybees?
Honeybees are an ideal insect candidate for testing number sense. While it would be unreasonable to expect honeybees to have the same level of cognitive abilities as chimpanzees, their abilities are nevertheless impressive, for example, the ability to know what to do, when, and where.
The scientists' experiments did not determine whether or not honeybees can count, or place numbers in sequential order. The test was whether or not they have number sense, e.g., whether they can distinguish between a pattern comprised of two or three elements.
Experimental design.
The scientists trained a group of honeybees in a maze to perform a "delayed-match-to-sample" test. It tested their ability to distinguish between the number of elements in a visual pattern.
In a typical test, a honeybee first entered the scientists' apparatus, at which point a sample pattern (such as dots) was encountered. After that, the honeybee flew through a 3 foot long tunnel, at which point another chamber was encountered.
In this chamber, two choice patterns were present, only one of which was identical to the original sample pattern. If the correct choice pattern was chosen, a hidden sugar solution reward was obtained (olfactory sense -- smell -- was not an issue here).
If the incorrect choice pattern was chosen, the honeybee was released from the apparatus, and allowed to try again. Pattern locations were altered regularly; this eliminated the honeybees' development of any directional preferences.
Honeybee number sense.
Training using two dot patterns was performed for 3 days total, after which time consistent successful performance levels were reached (improved from roughly 50% to roughly 70%). The honeybees' performance was enhanced by including breaks in training and including novel stimuli (shapes).
Similarly, the percentage of honeybees making an incorrect second choice, after making a correct first choice, declined rapidly. Initially it was roughly 50%, but eventually declied to roughly 25%.
The honeybees also performed well with three dot patterns. The shape of the stimuli was unimportant; it could be dots, stars, or lemons, and the sample patterns could be of a different size than the choice patterns.
Additionally, the initial sample pattern could be three dots, and the choice pattern could be three lemons; the honeybees still performed well. Collectively, this strongly suggests that the honeybees are making decisions based on number sense.
The honeybees did display a limit in their number sense. While they could successfully select a three-pattern over a four-pattern, they were not able to consistently select a four-pattern over a three-pattern; higher-number tests were also unsuccessful.
Evolutionary significance.
The ability of honeybees to discriminate between numbers could easily be of evolutionary benefit. For example, it could serve as directional cues, or aid in foraging behavior.
In any case, honeybees, an insect, do have a limited sense of numbers. This further closes the gap between the known capabilities of humans relative to other critters.
for more information:
Gross, H. J.; Pahl, M.; Si, A.; Zhu, H.; Tautz, J.; Zhang, S.
Number-based visual generalization in the honeybee.
PLoS ONE 2009, 4, e4263.