Fiddler crabs are unique in timing their escape responses based on speed-dependent visual cues.

Predation risk imposes strong selection pressures on visual systems to quickly and accurately identify the position and movement of potential predators. Many invertebrates and other small animals, however, have limited capacity for distance perception due to their low spatial resolution and closely situated eyes. Consequently, they often rely on simplified decision criteria, essentially heuristics or "rules of thumb", to make decisions.

Behavioural and neural responses of crabs show evidence for selective attention in predator avoidance.

Selective attention, the ability to focus on a specific stimulus and suppress distractions, plays a fundamental role for animals in many contexts, such as mating, feeding, and predation. Within natural environments, animals are often confronted with multiple stimuli of potential importance. Such a situation significantly complicates the decision-making process and imposes conflicting information on neural systems.

Evidence of predictive selective attention in fiddler crabs during escape in the natural environment.

Selective attention is of fundamental relevance to animals for performing a diversity of tasks such as mating, feeding, predation and avoiding predators. Within natural environments, prey animals are often exposed to multiple, simultaneous threats, which significantly complicates the decision-making process. However, selective attention is rarely studied in complex, natural environments or in the context of escape responses.

Countershading enhances camouflage by reducing prey contrast.

A three-dimensional body shape is problematic for camouflage because overhead lighting produces a luminance gradient across the body's surface. Countershading, a form of patterning where animals are darkest on their uppermost surface, is thought to counteract this luminance gradient and enhance concealment, but the mechanisms of protection remain unclear. Surprisingly, no study has examined how countershading alters prey contrast, or investigated how the presence of a dorsoventral luminance gradient affects detection under controlled viewing conditions.