Silk-mediated queueing migration in Cretaceous mites.

Queueing migration is among the most intriguing forms of collective behaviour in Metazoa, yet its origin and evolution in terrestrial arthropods remain poorly understood because fossil evidence of collective movement is exceedingly rare and largely confined to Palaeozoic marine taxa. Here, we document an exceptional case of queueing migration in larval mites, Protofilum ordinatum gen. et sp. nov. (Trombidiformes: Erythraeidae), preserved in mid-Cretaceous Burmese amber (approx. 100 Ma). This material represents the earliest known evidence of queueing behaviour in terrestrial arthropods and provides the first direct fossil evidence for the mechanism underlying queue formation. Remarkably, fine silk threads physically link the legs of adjacent individuals, and both the moment of silk extrusion and a distinct silk-producing apparatus are preserved. This discovery constitutes the first fossil evidence of silk use in mites. Our fossils reveal a previously unrecognized functional role for silk, acting as a direct mechanical connector that actively stabilizes the spatial organization of the moving queue. We propose that such coordinated migration could facilitate superparasitism and subsequent mate finding in these mites. Overall, these findings uncover unexpected behavioural sophistication in early minute arthropods and extend the deep-time record of queueing migration in terrestrial ecosystems.