Insect societies are tightly integrated, complex biological systems in which group-level properties arise from the interactions between individuals^1,2,3,4. However, these interactions have not been studied systematically and therefore remain incompletely known. Here, using a reverse engineering approach, we reveal that unlike solitary insects, ant pupae extrude a secretion derived from the moulting fluid that is rich in nutrients, hormones and neuroactive substances. This secretion elicits parental care behaviour and is rapidly removed and consumed by the adults. This behaviour is crucial for pupal survival; if the secretion is not removed, pupae develop fungal infections and die. Analogous to mammalian milk, the secretion is also an important source of early larval nutrition, and young larvae exhibit stunted growth and decreased survival without access to the fluid. We show that this derived social function of the moulting fluid generalizes across the ants. This secretion thus forms the basis of a central and hitherto overlooked interaction network in ant societies, and constitutes a rare example of how a conserved developmental process can be co-opted to provide the mechanistic basis of social interactions. These results implicate moulting fluids in having a major role in the evolution of ant eusociality.

昆虫社会是紧密整合的复杂生物系统，其中群体层面的特性源自个体之间的相互作用^1,2,3,4。然而，这些相互作用尚未得到系统研究，因此仍然不完全清楚。在这里，我们利用逆向工程方法发现，与孤独的昆虫不同，蚂蚁蛹会排出一种来自蜕皮液的分泌物，这种分泌物富含营养物质、激素和神经活性物质。这种分泌物会引起父母的照顾行为，并迅速被成虫清除和消耗。这种行为对于蛹的生存至关重要。如果不清除分泌物，蛹就会受到真菌感染并死亡。与哺乳动物的乳汁类似，分泌物也是早期幼虫营养的重要来源，如果幼虫无法接触到液体，就会出现生长迟缓和存活率下降的情况。我们表明，蜕皮液的这种衍生社会功能在蚂蚁中普遍存在。因此，这种分泌物形成了蚂蚁社会中迄今为止被忽视的核心互动网络的基础，并构成了如何利用保守的发育过程来提供社会互动的机械基础的罕见例子。这些结果表明换毛液在蚂蚁真社会性的进化中发挥着重要作用。