What is the venom of th Brown recluse Spider and how does it differ from the Black widow's venom?

Answer 1

Most Recluse spider bites are minor with no necrosis. However, a small number of bites produce severe dermonecrotic lesions, and, sometimes, severe systemic symptoms, including organ damage. Rarely the bite may also produce the systemic condition with occasional fatalities.
A minority of bites form a necrotizing ulcer that destroys soft tissue and may take months and very rarely years to heal, leaving deep scars. The damaged tissue will become gangrenous and eventually slough away. The initial bite frequently cannot be felt and there may be no pain, but over time the wound may grow to as large as 10 inches (25 cm) in extreme cases. Bites usually become painful and itchy within 2 to 8 hours, pain and other local effects worsen 12 to 36 hours after the bite with the necrosis developing over the next few days.Serious systemic effects may occur before this time, as the venom spreads throughout the body in minutes. Mild symptoms include nausea, vomiting, fever, rashes, and muscle and joint pain. Rarely more severe symptoms occur including hemolysis, thrombocytopenia, and disseminated intravascular coagulation. Debilitated patients, the elderly, and children may be more susceptible to systemic loxoscelism.

The widow spiders (genus Latrodectus), such as the black widow and red-back spider, are spiders that carry a neurotoxic venom which can cause a set of symptoms known as Latrodectism. Like many spiders, widows have very poor vision, and they move with difficulty when not on their web. Widow spiders are large, strong-looking house spiders (but still have relatively spindly legs and deep, globular abdomens). The abdomen is dark and shiny, and has one or several red spots, either above or below. The spots may take the form of an hourglass, or two triangles, point-to-point. Male widows, like most spiders, are much smaller than the females, and may have a variety of streaks and spots on a browner, less globular abdomen. The males are generally considered to be much less dangerous (if at all) than the females. Widows tend to be quite non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The venom, although rarely life-threatening, produces very painful effects including muscle spasms and 'tetanus-like' contractions. A serious bite will often require a short hospital stay. Children, elderly, and ill individuals are at most risk of serious effects.


Hope this helps!

Answer 2

Beetle's answer was pretty thorough. A shorter version might be something like this:
Venoms generally come in two types - "digestive" venoms (protein cocktails that break down tissues and lead to severe injury or death in the prey) and "paralyzer" venoms that interfere with nerve impulses and impair conscious movement. In spiders, recluses have 'necrotic' venom, while widows have neurotoxic venom. Similarly, rattlesnakes have necrotic venome while Coral Snakes (like cobras) have neurotoxic venom. One big difference in effect between the two is that necrotic venoms tend to be more dangerous as you get more delivered, while neurotoxic venoms are bad even if you get a very small amount delivered.