Image of a jumping spider. Dahl and Cheng (CC BY 4.0)
Recognising familiar individuals helps animals navigate their social lives, including finding mates, avoiding rivals, and caring for their young. This skill, called individual recognition, is often linked to social species with large brains, and it supports higher cognitive functions such as empathy, reputation tracking, and attributing mental states.
Recognising an individual requires memory and flexible matching across viewpoints and lighting, and larger brains have more neurons and brain areas that respond strongly to faces. Jumping spiders are tiny hunters with excellent vision, but they are mostly solitary and rarely encounter the same spider twice. Previous studies showed that these animals can distinguish species and sex using colours and patterns. However, it was less known whether a jumping spider can also recognise a specific individual.
To find out more, Dahl and Cheng set up face-to-face meetings between regal jumping spiders (Phidippus regius) while keeping them safely separated by transparent panels. Overhead video tracked how close the pair chose to be. Mutual distance was treated as a simple readout of interest, while moving closer suggested stronger attention to the other spider. Keeping distance indicated reduced interest or growing familiarity.
When a spider first saw another individual, it often approached. If the same pair met again minutes later, they tended to keep a bit more distance, consistent with becoming familiar with that specific spider. But when the next encounter featured a different individual, the spiders moved closer, showing increased interest. Across many controlled pairings, this clear behavioural switch between familiar and new repeated reliably.
The effect weakened as the same individuals were shown repeatedly across sessions, even hours later, potentially indicating that the spiders were building up familiarity. Introducing a completely new individual at the end of the experiment – after hours of testing – produced the strongest renewed interest. This late rebound is inconsistent with general fatigue or waning motivation. If spiders were merely tired, an approach would be expected to drop for all stimuli. Instead, this points to sensitivity to individual novelty. In other words, the spiders retain information about who they have seen and retrieve this information after delays – a pattern consistent with encoding and storing individual-specific visual features and comparing new views against that record.
These findings invite a shift in perspective. If a tiny, mostly solitary spider can recognise individuals, how much brain is really needed for flexible social memory? We may underrate animals with compact nervous systems because we treat brain size as a stand-in for cognition. What do such abilities imply for debates about animal consciousness? Behaviour cannot prove subjective experience, but it narrows what kinds of minds are plausible. Future work can map individual recognition across animal groups using the same test. It can then test whether the pattern tracks lifestyle and sensory systems more than brain size, and whether the trait evolved many times independently or from an ancient common origin.
