Animal behavior: Timing escape on angular size or angular velocity?

Animals avoid rapidly approaching objects. In many arthropods, angular size is a common visual cue used to decide the time of avoidance. A new study shows that fiddler crabs decide when to escape based on object angular expansion velocity. Animals avoid rapidly approaching objects. In many arthropods, angular size is a common visual cue used to decide the time of avoidance. A new study shows that fiddler crabs decide when to escape based on object angular expansion velocity.