1. Key Points

• The study tracks, over a single night, the flow of brood food produced by 100 nurse bees in two normal-sized colonies.
• It shows that this brood food does not go exclusively to the brood: a substantial proportion is also donated to adult bees, including older workers, foragers, and drones.
• During the observation night, very young larvae were identified less frequently as recipients of this food than older larvae.
• Among adults, the youngest workers receive jelly on average more often and in larger quantities than older ones, but exchanges extend broadly across the entire colony.
• For the apiary, the primary value is one of understanding: nurse bees convert pollen-derived proteins into brood food via their glands, and this food supports not only the brood but also a significant proportion of adult bees. The precise proportions should, however, be read with caution, as the study covers only two colonies and a single night.

2. What the Study Shows

This older but important study describes the colony as an active system of protein redistribution through the nurse bees.

Research question. Karl Crailsheim set out to quantify the flow of "jelly" within a honeybee colony. In this context, the term does not refer solely to royal jelly in the strict sense, but more broadly to the protein-rich brood food produced by nurse bees via their hypopharyngeal glands. The question is straightforward yet important: does this food serve almost exclusively the brood and the queen, or does it also circulate in substantial amounts among adult bees?

Method. The study was conducted in Austria, under temperate central European conditions broadly comparable to those of many Swiss apiaries, using two colonies of Apis mellifera carnica occupying 9 to 10 combs, during full brood-rearing season. In each colony, 100 nine-day-old nurse bees were injected with a radiolabelled amino acid (¹⁴C-phenylalanine). After one night in the colony, the author measured where the marker had been redistributed: in workers of different age classes, in identified foragers, in drones, in larvae at different developmental stages, and in honey and bee bread. The aim was to trace not each individual exchange, but the final destination of a portion of the proteins processed by the nurse bees.

Results. The central finding is clear: brood food does not go only to the larvae. The two colonies, however, differ markedly in the precise distribution between adults and brood. In the first colony, a substantial proportion of the jelly distributed by nurse bees was recovered in adult bees, whereas in the second colony the proportion reaching the larvae was considerably higher. In figures, colony 1 shows approximately 52 % of the recovered jelly in the workers, while in colony 2 this share falls to approximately 39 %, with the proportion recovered in worker larvae rising to around 66 %. In a single night, the jelly from these 100 nurse bees reached approximately 9.6 % and 15.6 % of all workers depending on the colony, and 17.5 % of a large sample of drones. Among workers, the youngest adults received jelly more frequently and, on average, in greater amounts than older individuals. Among larvae, slightly more advanced developmental stages were most frequently identified as recipients during the measured night. No radioactivity was detected in honey or bee bread samples.

Interpretation. The study thus supports the view that nurse bees act as colony-wide protein redistributors, not merely as brood nurses. More specifically, they convert the protein resources they consume into brood food and then redistribute this glandular food to other members of the colony. The finding is particularly noteworthy for foragers and drones: even though they consume little or no pollen directly, they nevertheless receive proteins in an already processed form via trophallaxis. The author also proposes that the substantial exchanges among nurse bees themselves may carry a social information function, but this point is more a matter of interpretation than direct demonstration.

In other words, the study invites us to view the colony not as a collection of individuals each feeding independently, but as a system in which a significant fraction of protein nutrition passes through the nurse bees as brood food before being redistributed. This is probably its most useful contribution for the beekeeper: a better appreciation that the condition of the nurse bees and their nutritive secretions influences the colony far more broadly than brood rearing alone.

3. Critical Assessment

The results are striking, but they come from a demanding protocol conducted on very few colonies and over an extremely short period.

Strengths of the study. For its time, the protocol is ambitious. It tracks a metabolic tracer in normal-sized colonies rather than simplified cage setups or very small groups. The author does not focus solely on the brood: he compares several worker age classes, includes foragers, drones, the queen, and multiple larval stages. The study thereby documents an often underappreciated aspect of social biology: the internal circulation of proteins. Related studies published subsequently point broadly in the same direction and lend greater biological plausibility to the concept of protein redistribution by nurse bees, even if they do not all replicate exactly the same experimental design (Crailsheim, 1991; Lass & Crailsheim, 1996; Camazine et al., 1998).

Methodological limitations. Caution remains necessary nonetheless. First, the study covers only two colonies and a single night. It thus provides a useful snapshot, not a general mean valid across all colonies, seasons, and conditions. Second, the method rests on several assumptions and extrapolations: detection thresholds, estimation of the colony's age structure, calculation of "jelly spent" from the label not recovered in the nurse bees. The fact that the overall label recovery balance is 69 % in one colony and 106 % in the other reflects more than ordinary imprecision: a result above 100 % indicates that reconstruction of the flow reaches its methodological limits and that a portion of the calculations is highly sensitive to the assumptions made.

Possible biases and confounds. The differences between the two colonies are themselves very pronounced. In one, the proportion recovered in adults is markedly higher; in the other, larval brood predominates. The author advances plausible biological explanations: brood quantity, physiological condition of the nurse bees, behavioural differences between colonies. This variability also means, however, that it would be inadvisable to convert the observed percentages into a practical rule. Moreover, the study tracks the fate of a specific group of nine-day-old nurse bees; it does not directly describe the entirety of trophallactic exchanges across the whole colony. Subsequent studies therefore strengthen the general mechanism more than the specific numerical proportions observed here.

What cannot be concluded. This study does not demonstrate that all adult bees depend to the same degree on brood food. Nor does it support the conclusion that a pollen deficit will automatically translate, in any given apiary, into a specific measurable decline in foragers or drones. Finally, it does not in itself justify systematic protein supplementation: it illuminates a biological mechanism without testing a practical intervention at the apiary. Complementary studies also suggest that this protein redistribution may participate in broader colony-level regulation of pollen foraging, but this functional role remains largely mechanistic and does not translate directly into a simple practical management recommendation (Camazine et al., 1998).

It should also be recalled that this is a study published in 1992. That does not diminish its foundational value, but it does invite us to read it as a highly instructive study in social biology rather than as a ready-made technical recommendation.

4. What Related Studies Show

The most closely related studies point broadly in the same direction. In small free-flying colonies, Crailsheim had already shown that nurse bees labelled with ¹⁴C-phenylalanine transferred brood food not only to the queen and brood but also to workers of different ages, to nurse bees of the same age, to foragers, and to young drones (Crailsheim, 1991). The 1992 study extends this finding to normal-sized colonies: the result is therefore less an isolated observation than a coherent line of evidence (Crailsheim, 1991, 1992).

Subsequent studies primarily refined the biological framework of this redistribution. A 1996 study showed that caged bees continued to feed other adult bees, but with less developed hypopharyngeal glands and a markedly lower quantity of proteinaceous food transferred compared with same-aged bees that had remained in the colony (Lass & Crailsheim, 1996). In 1998, another study suggested that this protein trophallaxis may also serve a signalling function: as pollen stores increased, nurse bees transferred greater quantities of labelled proteins in the form of glandular food to pollen foragers, who in turn rapidly reduced their collection activity (Camazine et al., 1998).

Finally, a more recent study contributes primarily a useful methodological complement. Langlands et al. (2021) confirmed that ¹⁴C-phenylalanine labelling reliably tracks the trophallactic transfer of hypopharyngeal proteinaceous secretions. However, the recipients in that study were small hive beetles rather than adult colony bees: this work therefore supports the general mechanism and experimental approach without constituting a direct replication of the central result observed by Crailsheim.

Overall, the studies converge in describing nurse bees as a colony-level protein redistribution centre, even though few measure this flow as directly as the 1992 article (Crailsheim, 1991; Lass & Crailsheim, 1996; Camazine et al., 1998; Langlands et al., 2021).

5. Practical Implications for the Apiary

For the apiary, this study is primarily useful for better understanding the central role of nurse bees in the colony's protein economy.

• Brood food does not nourish only the brood and the queen: it also sustains a significant proportion of the adult bee population.
• A shortage of pollen resources may therefore have diffuse effects throughout the colony, not merely on the larvae visible at the centre of the brood nest.
• Related studies also suggest that this protein redistribution may participate in colony-level regulation of pollen foraging activity, which reinforces the importance of monitoring pollen stores as well as the dynamics of the nurse bee population, especially in spring and during active brood-rearing periods (Camazine et al., 1998).
• This finding does not, however, justify routine protein supplementation on its own, nor does it support hasty conclusions about the nutritional status of a colony.
• The observed proportions should not be transposed directly to the Swiss apiary context: they are likely to depend on the season, the volume of brood, and the individual condition of each colony.

Further reading on ApiSavoir

• Pollen consumption and colony development
• Vitellogenin and the keys to the colony
• Principles of bee feeding
• Bee behaviour inside the hive: findings from a long-term video analysis
• From egg to imago

References

Camazine, S., Crailsheim, K., Hrassnigg, N., Robinson, G. E., Leonhard, B., & Kropiunigg, H. (1998). Protein trophallaxis and the regulation of pollen foraging by honey bees (Apis mellifera L.). Apidologie, 29(1–2), 113–126. https://doi.org/10.1051/apido:19980107

Crailsheim, K. (1991). Interadult feeding of jelly in honeybee (Apis mellifera L.) colonies. Journal of Comparative Physiology B, 161(1), 55–60. https://doi.org/10.1007/BF00258746

Crailsheim, K. (1992). The flow of jelly within a honeybee colony. Journal of Comparative Physiology B, 162(8), 681–689. https://doi.org/10.1007/BF00301617

Langlands, Z., du Rand, E. E., Crailsheim, K., Yusuf, A. A., & Pirk, C. W. W. (2021). Prisoners receive food fit for a queen: honeybees feed small hive beetles protein-rich glandular secretions through trophallaxis. Journal of Experimental Biology, 224(2), jeb234807. https://doi.org/10.1242/jeb.234807

Lass, A., & Crailsheim, K. (1996). Influence of age and caging upon protein metabolism, hypopharyngeal glands and trophallactic behavior in the honey bee (Apis mellifera L.). Insectes Sociaux, 43(4), 347–358. https://doi.org/10.1007/BF01258408

Wang, Y., Ma, L., Zhang, W., Cui, X., Wang, H., & Xu, B. (2016). Comparison of the nutrient composition of royal jelly and worker jelly of honey bees (Apis mellifera). Apidologie, 47(1), 48–56. https://doi.org/10.1007/s13592-015-0374-x