Willow caterpillar infestationm

Willow caterpillar infestationm

Observation - Willow caterpillar infestationm. Description: Hundreds of these busy denuding a small garden willow on the east coast of central Scotland. What kind of caterpillar is it?

Hundreds of these busy denuding a small garden willow on the east coast of central Scotland. What kind of caterpillar is it?