precise mechanisms are not well understood. Acetylcholine release accounts for neuromuscular manifestations, and norepinephrine release accounts for the cardiovascular manifestations. Female redbacks have an average of around 0.08–0.10 mg of venom, and experiments indicate that the median lethal dose (LD50) for mice at room temperature is 10–20% of this quantity (0.27–0.91 mg/kg based on the mass of the mice used), but that it is considerably deadlier for mice kept at lower or higher temperatures. Pure alpha-latrotoxin has an LD50 in mice of 20–40 µg/kg. The specific variant of the vertebrate toxin found in the redback was cloned and sequenced in 2012, and was found to be a sequence of 1180 amino acids, with a strong similarity to the equivalent molecule across the Latrodectus mactans clade. The syndromes caused by bites from any spiders of the genus Latrodectus have similarities; there is some evidence there is a higher incidence of sweating, and local and radiating pain with the redback, while black widow envenomation results in more back and abdominal pain, and abdominal rigidity is a feature common with bites from the west coast button spider (Latrodectus indistinctus) of South Africa. One crustacean-specific and two insect-specific neurotoxins have been recovered from the Mediterranean black widow (L. tredecimguttatus), as have small peptides that inhibit angiotensin-1-converting enzyme; the venom of the redback, although little-studied, likely has similar agents. Antivenom Redback antivenom was developed by Commonwealth Serum Laboratories, then a government body involved with discovering antivenoms for many venomous Australian creatures. Production involves the milking of venom from redbacks and repeatedly inoculating horses with non-lethal doses. The horse immune systems makes polyclonal antibodies. Blood plasma, containing the antibodies, is extracted by plasmapheresis. The plasma is treated with pepsin, and the active F(ab')2 fragments are separated and purified. Each vial contains 500 units of redback antivenom in approximately 1.5 ml, which is enough to inactivate 5 mg of redback spider venom in a test tube. The antivenom has been safely administered to women in various stages of pregnancy. Redback antivenom has been widely used in Australia since 1956, although evidence from controlled studies for its effectiveness has been lacking. Recent trials show antivenom has a low response rate little better than placebo, and any effect is less than might be achieved with optimal use of standard analgesics. Further studies are needed to confirm or refute its effectiveness. It appears clinically active against arachnidism caused by Steatoda