The Fantastic Communication Systems of Social Insects

The ability to communicate is important for societies to function well. In human societies, communication takes many forms—spoken language, writing, facial expressions, body language, and even digital messages—and allows people to coordinate tasks, express needs, and respond to shared goals—whether within families, workplaces, or entire communities. For social insects, communication helps them notice when the colony needs more food, for example. When a bee finds a food resource, she can communicate with other bees to indicate where the food sources are located. This type of communication exists in societies of ants, bees, termites, and wasps. Inside a colony of social insects, individuals share the various daily activities [1]. For example, one or a few females are responsible for producing new eggs, which will develop into new adults that either stay in the colony or leave it to start one of their own. Everyone inside a colony cooperates to care for the young ones. Many researchers are interested in understanding how social insects coordinate their lives, which may help them to understand how other animal societies function.

Examples of Communication in Social Insects

Communication involves two “types” of individuals: senders and receivers. Senders produce a message and receivers receive the message. The main objective of sending a message is to change the receiver’s behavior in some way. Communication within colonies of social insects normally involves adult-adult and adult-young interactions.

Here are few examples of adult-adult communication in social insects:

• Honeybees dance to communicate where food is located. When a honeybee finds a patch of flowers, it returns to its colony and informs the others of the direction and the distance of the food source, using dance moves (Figure 1A).

• Ants can release a trail of odors when they are searching for food, which helps other members locate the food source more quickly. The odor trail also prevents the ants from getting lost along the way (Figure 1B).

• Paper wasps recognize each other through visual marks on their heads, kind of like how humans recognize faces (Figure 1C).

Communication involving adult-young organisms in social insects includes:

• Honeybee larvae cannot move, so they cannot search for food on their own. Hungry larvae produce and release odors that inform adult honeybees that they need to be fed. When adult honeybees detect those messages, they leave the colony to search for flowers.

• Instead of constructing their own homes, some paper wasp females invade other colonies to put their eggs there, similar to the behavior of the cuckoo bird. However, this is not good for the resident wasp. The resident wasp can distinguish the smell of their own eggs from those that do not belong to them, and they can remove strangers’ eggs from their nests.

Knowing who belongs and who does not belong to their colonies is very important for social insects. The process of distinguishing an individual who lives in the nest from one that does not live there is called nestmate recognition.

Friends or Foes?

Nestmate recognition has been studied in several social insect species, including several species of bees. Different types of odors help resident individuals perform nestmate recognition. One class of odors are created by chemical compounds called cuticular hydrocarbons, which contain various combinations of hydrogen and carbon molecules. Cuticular hydrocarbons cover the insects’ bodies, and whenever individuals touch each other with their antennae (called antennation), they can learn about each other’s identity and who belongs to their nest (Antennae have a similar function to the human nose, but with a much stronger ability to detect smells and flavors). These chemicals can also be found on the nest and on the bodies of young individuals (eggs, larvae, and pupae).

To keep unknown individuals out of the nest, many bee species have a group of females at the nest entrance, checking individuals’ “chemical IDs” and determining whether they can enter or not. These individuals are called guards or soldiers. In one tropical bee species called Tetragonisca angustula, in addition to soldiers found around the nest entrance tube (Figure 2A), a second group of bees, called “hover soldiers”, flies around the nest entrance to intercept intruders [2]. In this species, the larger the soldier, the better they are at recognizing nest intruders, because their antennae have an improved ability to smell [3]. In our study, we decided to investigate how other Brazilian stingless bees recognize their friends.

Exploring Recognition Abilities in Stingless Bees

We studied nestmate recognition in two tropical stingless bee species that have funny-sounding popular names: uruçu and mandaçaia [4]. These bees have traditionally been kept by native populations in the Americas and still have great relevance for both cultural and commercial practices. Uruçu nests are found in tree hollows, and they are distributed in the north and northeast of Brazil. Mandaçaia bees are found across Argentina, Paraguay, and Brazil. Their nests are also located in tree hollows, and the nest entrances have traces of mud around it. In our study, their nests were transferred to wooden boxes and they were placed in a laboratory, which helped us with our observations and experiments. To check if the guard females of both species could recognize their nestmates (others from the same nest) over non-nestmates from other colonies, we created encounters between females that were returning from the field with food (called foragers) and the resident guards.

Observing Recognition and Acceptance in Stingless Bees

To easily observe the bees’ interactions, we placed a plastic box with a transparent cover lid in front of each nest box that we used. Each nest received either forager females that did not belong to the nest box or females that did belong to it. If the resident guards of each nest box could recognize the bees we added, we expected they would attack those that did not live with them but would not attack nestmates. We repeated this procedure with several nests, setting up many encounters between foragers and guards. If a forager was bitten by the resident guards—they bite with their mandibles, which are their mouth structures—this was classified as being rejected, whereas those foragers received only with antennation (Figure 2B) were classified as being accepted.

For uruçu bees, we found that nestmate foragers were more accepted by resident guards compared to non-nestmates. 84% of nestmate bees were accepted in their original nests, and only 42% of non-nestmate bees were accepted in nests they did not belong to (Figure 3A). The likelihood of being accepted was determined by how far away their original nests were located. Non-nestmate foragers belonging to closer nests were more likely to be accepted (Figure 3B).

For mandaçaia bees, we also detected that nestmates were more likely to be accepted than non-nestmates. However, the difference was not as high as it was for uruçu bees. For mandaçaia, 49% of nestmate bees were accepted into their original nests, compared to 42% of non-nestmate bees (Figure 3C). For this species, the distance between nests did not affect the chances of acceptance (Figure 3D).

Distinguishing Nestmates From Non-Nestmates Varies Among Species

The two stingless bee species that we studied accepted or rejected nestmate and non-nestmate bees in different proportions. Compared to mandaçaia guards, the guards of uruçu were better at distinguishing between who was and who was not from their nest. These results led us to two conclusions. First, we concluded that different species can have different tolerance levels toward intruders. Second, at least for some bees, nest distance can determine the flow of individuals among unrelated nests, since the scent and presence of nearby neighbors are more familiar compared to distant ones. In our study, the mandaçaia nests were closer to each other than those of uruçu. That said, the odor similarity among mandaçaia bees from different nests may have facilitated the movement of bees from the neighborhood during our experiments. Our results suggest that different species may use information in their own way when deciding who belongs and who does not to their colonies. A next step would be to explore what happens in the long run when colonies allow outsiders to join, and whether the effects are different for species that are more or less strict. Studying other Melipona bees could also give us a clearer picture of the general strategies they use for recognizing nestmates.

Glossary

Colony: ↑ A big family of ants, bees, termites or wasps that live together. The adults work as a team to find food and take care of the young ones.

Paper Wasps: ↑ Wasps that build nests out of paper made by chewing wood and mixing it with their saliva.

Larvae: ↑ Baby insects that look like little worms before they grow into adult bees, butterflies, or other bugs.

Nest: ↑ Place where ants, bees, and wasps live.

Nestmate: ↑ It represents the insect mate that comes from the same colony as you.

Cuticular Hydrocarbons: ↑ Chemical compounds made of hydrogen and carbon molecules, which cover the body of insects.

Antennation: ↑ The behavior insects do to sense different smells by moving their antennae and touching the surfaces.

Pupae: ↑ Insects resting inside a cocoon or shell, changing from larvae into adults.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We would like to acknowledge the agencies that gave us the necessary resources to allow the study to be performed. This work was supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES) (JB and RCS); Conselho Nacional de Desenvolvimento Científico e Tecnológico under Grant 88887.369636/2019–00 (FSN); Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) under Process 2018/22461–3 (RCS) and Process 2021/05998-8 (FSN); FWO G0F6622N and G0F8319N (CAO and RCO). RCS also received support from the FYSSEN and SOUND initiative while editing this manuscript.

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