Bold Jumping Spider

Lore & Background

Portia spiders are known for their intelligent hunting tactics. All members of *Portia* have instinctive hunting tactics for their most common prey, but can improvise by trial and error against unfamiliar prey or in unfamiliar situations, and then remember the new approach. They exhibit spatial memory and object permanence, and are capable of trying out a behavior to obtain feedback regarding success or failure, and they can plan ahead, as it seems from their detouring behavior. *Portia* species can make detours to find the best attack angle against dangerous prey, even when the best detour takes a *Portia* out of visual contact with the prey, and sometimes the planned route leads to abseiling down a silk thread and biting the prey from behind. Such detours may take up to an hour, and a *Portia* usually picks the best route even if it needs to walk past an incorrect route. Nonetheless, they seem to be relatively slow thinkers, as is to be expected since they solve tactical problems by using brains vastly smaller than those of mammalian predators. *Portia* has a brain significantly smaller than the size of the head of a pin, and it likely has less than 100,000 neurons (for comparison, a mouse brain has about 70 million neurons and a human brain has 86 billion). *Portia* can distinguish their own draglines from conspecifics', recognizing self from others, and also discriminate between known and unknown spiders.

In Their Own Story

When stalking web-building spiders, *Portia* try to make different patterns of vibrations in the web that aggressively mimic the struggle of a trapped insect or the courtship signals of a male spider, repeating any pattern that induces the intended prey to move towards the *Portia*. *Portia fimbriata* has been observed to perform vibratory behavior for three days until the victim decided to investigate. They time invasions of webs to coincide with light breezes that blur the vibrations that their approach causes in the target's web, and they back off if the intended victim responds belligerently. Other jumping spiders take detours, but *Portia* is unusual in its readiness to use long detours that break visual contact. Laboratory studies show that *Portia* learns very quickly how to overcome web-building spiders that neither it nor its ancestors would have met in the wild. *Portia*'s accurate visual recognition of potential prey is an important part of its hunting tactics. For example, in one part of the Philippines, local *Portia* spiders attack from the rear against the very dangerous spitting spiders, which themselves hunt jumping spiders. This appears to be an instinctive behavior, as laboratory-reared *Portia* of this species do this the first time they encounter a spitting spider. On the other hand, they will use a head-on approach against spitting spiders that are carrying eggs.

Reader's Guide

The 17 described species of *Portia* are found in Africa, Australia, China, Madagascar, Malaysia, Myanmar, Nepal, India, the Philippines, Sri Lanka, Taiwan, and Vietnam. *Portia* are vulnerable to larger predators such as birds and frogs, which a *Portia* often cannot identify because of the predator's size. Some insects prey on *Portia*, for example, mantises, the assassin bugs *Nagusta* sp. indet. and *Scipinnia repax* (that is, *Scipinia rapax*). When not hunting for prey or a mate, *Portia* species adopt a special posture, called the "cryptic rest posture", pulling their legs in close to the body and their palps back beside the chelicerae ("jaws"), which obscures the outlines of these appendages. When walking, most *Portia* species have a slow, "choppy" gait that preserves their concealment: pausing often and at irregular intervals; waving their legs continuously and their palps jerkily up and down; moving each appendage out of time with the others; and continuously varying the speed and timing. When disturbed, some *Portia* species are known to leap upwards about 100 to 150 millimetres (4 to 6 in) often from the cryptic rest pose, and often over a wide trajectory. Usually the spider then either freezes or runs about 100 millimetres (4 in) and then freezes.

Did You Know?

• Portia was established in 1878 by German arachnologist Ferdinand Karsch.
• Portia fimbriata has been observed performing vibratory behavior for three days until the victim decided to investigate.
• Portia has a brain significantly smaller than the size of the head of a pin, with likely less than 100,000 neurons.
• Portia can distinguish their own draglines from conspecifics', recognizing self from others.
• Some specimens found trapped in Oligocene amber were identified as related to Portia.