For a spider bite to be regarded as a definite bite (by a particular type of spider), all of the following must occur:

• Evidence of a bite: clinical effects at the time or soon after the bite, including discomfort or pain;
• Collection of the spider at the time or immediately after the bite;
• Identification of the spider by an expert arachnologist.

Discomfort or pain always occurs with spider bites; their absence goes against the diagnosis. Other important local effects include:

• Fang marks/bleeding are indicative of fang size and so the size of the spider;
• Erythaema/red mark;
• Itchiness (immediate or delayed);
• Swelling/oedema is uncommon.

Over 80% of bites are caused by 6 major families of spiders:

• Orb weavers (Araneidae )
• Huntsmen (Sparassidae )
• White-tail spiders (Lamponidae :Lampona spp.)
• Redback spiders (Latrodectus hasselti) and cupboard spiders (Theridiidae )
• Wolf spiders (Lycosidae )
• Jumping spiders (Salticidae )

The majority of cases of bites involving these spiders result in local pain alone. Systemic effects are rare and mild.

Medscape Spider Slide Show