Ryan Photographic - Salticidae - Jumping Spiders

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Family Salticidae

Even many folk who don't like spiders make an exception for jumping spiders. Highly visual predators they have some of the best eyes amongst the arthropods. Perhaps it is the large size of their anterior medial eyes that people find attractive. For me it is their lively "intelligence". Jumping spiders will turn to face you as you approach and will often change position several times while they "size you up". There are over 600 genera of salticids and more than 5800 described species which makes them the most speciose spider family. Thirteen percent of spider species are jumping spiders which suggests that the life style is highly successful.

The salticids stalk their prey before lunging at them and striking with their fangs. They injecta powerful venom which almost immediately immobilizes their prey. As alluded to above they have extraordinary eyes which can see into the ultraviolet. They may have better color vision than we do. Surprisingly they don't use stereo vision from the large anterior medial eyes. Instead they are built like telescopes with four separate retinal layers. The bottom-most layer sharply focuses green light while the layer above it detects unfocused light. The spider measures the amount of defocus from the fuzzy layer and uses this to determine distance (and all of this goes on in that tiny brain). You can read more about this here.

Most jumping spiders will secrete a silken thread and attach it before stalking prey. If they are brushed off or fall they can rapidly return to their position. These active spiders are unusual amongst arachnids in that they possess both book lungs (like most self-resepcting spiders) and tracheae.

Some salticids mimic ants with their front pair of legs waving about like ant antennae. Indeed, some salticids specialize in devouring ants - a dangerous occupation that has the benefit of a plentiful food supply. Several salticid species drink nectar and at least one species is a vegetarian. Amazing beasties - well worth a second look.