The caterpillars below have likely consumed all available resources in one place and are moving together to find more food or pupate. The video isn’t well focused, but it does illustrate the pile of caterpillars moving as one ‘slug’ across the stair.
A small group of us hiked to some newly acquired abandon pasture at the Las Cruces Biological Station that sits at the highest elevation of the reserve–1400 m. The northeastern view looks at the Talamanca mountain range, where Las Alturas de Coton is located, and, more broadly, La Amistad International Biosphere Reserve, which is a protected area covering southern Costa Rica and norther Panama.