They possess 8 eyes and are known to have the sharpest vision of all spiders, important for hunting ability. The arrangement of the eyes, four big eyes on the face and four smaller eyes on top of the head, distinguished Saltids from other spiders.(3) The larger pair of eyes (anterior median on the face) apparently serve for sharp vision, and the others for peripheral vision. Since the lenses of these eyes are relatively fixed, the internal eye muscles serve to move the retina. Because the retina is the darkest part of the eye and it moves around, one can sometimes look into the eye of a jumping spider and see it changing color. When it is darkest, you are looking into its retina and the spider is looking straight at you.(4)

These spiders apparently have dichromic vision with spectral sensitivities in the green and ultraviolet range.(5) (Ultraviolet vision is apparently common in the insect and arachnid world.) They depend much upon their sense of sight to hunt or to court. It is apparently for this reason that many jumping spiders have iridescent markings or colors on their bodies, legs and chelicerae. In P. audax, the chelicerae are iridescent green.(6)

Jumping spiders are carnivores and predators. They eat insects and other spiders. These spiders do not spin webs but make little silken shelters under leaves or bark.(1)

Saltids are the most common biting spider in the United States.(7) Persons gardening appear to be at risk for disturbing the habitat of this spider which may react by jumping on exposed skin and inflicting a bite. The bite is usually asymptomatic to slightly painful and subsequently results in a local reaction such as an erythematous papule or a small urticarial wheal.
 

REFERENCES

1. Jumping Spiders (Family Salticidae) in Lorus and Margery Milne, The Audubon Society Field Guide to North American Insects and Spiders. Alfred A. Knopf, New York, 1980. page 910
2. Richman David B. Status of Jumping Spider (Araneae Salticidae) Taxonomy worldwide. http://dns.ufsia.ac.be/Arachnology/Pages/Documents/Salticid.html
3. Saltids. http://spiders.arizona.edu/salticidae/salticidae.html
4. Wayne Maddison Jumping spider vision. http://spiders.arizona.edu/salticidae/ ++salticidae/anatomy/vision.html
5. De Voe RD. Ultraviolet and green receptors in principal eyes of jumping spiders. Journal of General Physiology, 1975 Aug, 66(2):193-207.
6. The Jumping Spider http://www.state.mo.us/conservation/nathis/ arthropo/mospider/spider.html
7. Spiders http://www.nitehawk.dk/CarlsenRanch/newsl/animal/spiders.htm

Velvet Mites
Latin name: Trombidium holosericeum
Size: Approximately 5mms
Distribution: Found throughout the U.K.
Months seen: April to October
Food: Tiny insects and other mites
Habitat: Gardens and deciduous woods
Special features: These arachnids are often seen wandering on bare soil or through grass. They are bright red and covered in tiny hairs which gives them a velvet appearance - hence the name.

Like other mites, they have no antennae. The front pair of legs are used as feelers to check where they're going.
The larvae are parasitic. After hatching from eggs laid in the soil, they latch themselves onto passing spiders or insects and suck their blood. They do not injure their hosts, and after a while drop off. They then burrow into the soil, moult and emerge as adults.

More information on Velvet Mites may be found at http://chicagowildernessmag.org/issues/fall2004/mite.html