Ever seen such an aggregation of firebugs (
pyrrhocoris apterus)?
For me it's the first time. But thanks to
German Wikipedia I could find this description (translated):
"
The common firebug is often found in aggregations with different stages of development. One can often find hundreds of individuals in sunny places or at the base of trunks of lime trees. The aggregations are held together by pheromones. However, due to the secretion of defence secretions, which also act as an alarm pheromone, they quickly dissolve."
This indeed was a lime tree. And note the different stages of development.
5D4, 24-105L @105mm, second pic close to MFD.