| Portia | |
|---|---|
| female P. fimbriata | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Arachnida |
| Order: | Araneae |
| Family: | Salticidae |
| Subfamily: | Spartaeinae |
| Genus: | Portia Karsch, 1878 |
| Type species | |
| Salticus fimbriatus Doleschall, 1859 |
|
| Species | |
|
see text |
|
| Diversity | |
| 17 species | |
Portia is a genus of jumping spider which feeds on other spiders (araneophagic). They are remarkable for their hunting behaviour which suggests they are capable of learning and problem solving, traits normally attributed to much larger animals.[1]
Contents |
The 17 described species are found in Africa, Australia, China, Malaysia, Myanmar, Nepal, India, Sri Lanka, the Philippines, and Vietnam.
Portias often hunt in ways that seem intelligent.[2] Their favorite prey appears to be web-building spiders between 10% and 200% of the Portia’s size. Portias look rather like leaf detritus caught in a web, and this is often enough to fool web-building spiders, which have poor eyesight.[2] When stalking web-building spiders, Portias 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.[3] 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 their approach causes in the target's web; and they back off if the intended victim responds belligerently. Portias that retreat may approach along an overhanging twig or rock, descend down a silk thread and kill the prey. Other jumping spiders take detours, but Portia is unusual in its readiness to use long detours that break visual contact.[3]
Laboratory studies show that Portia learns very quickly how to overcome web-building spiders that neither it nor its evolutionary 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 Portias 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. However, experiments that pitted Portias against "convincing" artificial spiders with arbitrary but consistent behavior patterns showed that Portia’s instinctive tactics are only starting points for a trial-and-error approach from which these spiders learn very quickly.[3] Nonetheless, they seem to be relatively slow "thinkers", as they solve tactical problems by using brains vastly smaller than mammalian predators'.[2] Against other jumping spiders, which also have excellent vision, Portias may mimic fragments of leaf litter detritus. When close to biting range, Portias use different combat tactics against different prey spiders. On the other hand they simply stalk and rush unarmed prey such as flies,[4] and also capture prey by means of sticky webs.[3]
Portia exhibits a different mating behavior and strategy compared to other jumping spiders. In most jumping spiders, males mount females to mate. In Portia the female drops a dragline after the male mounts her, mating in mid-air. Before this happens the male shows off his legs and extends them stiffly and shakes them to attract the female. The female then drums on the web. Mating with Portia spiders can occur off or on the web. The spider also practices cannibalism before and after copulation. The female usually twists and lunges at the mounted male (P. fimbriata however, is an exception; it does not usually exhibit such behavior.). If the male is killed before completing copulation, the male sperm is removed and the male is then eaten. If the male finishes mating before being killed, the sperm is kept for fertilization and the male is eaten. A majority of males are killed during sexual encounters.