Technically speaking, the northern funnel-web spider has the most lethal venom of any other spider in the world. However, a close competitor is the Sydney funnel-web spider. The venom of both spiders can lead to death in humans, but have never affected animals. These spiders are very fast, and unlike most spiders, aggressive towards people. The combination of these factors makes them the most dangerous spiders in the world.

The northern funnel-web as well as the Sydney funnel-web can only be found in Australia, and the northern funnel-web spider is usually found in the Australian woodland far from and rarely seen by people. The northern funnel-web spider is the more lethal of the two, but the Sydney funnel-web spider is the cause of most concern because it can live in or near homes.

Non-lethal funnel-web spiders are found in both North and South America.

The venom of these deadly spiders consists of a low molecular weighted toxin called "atracotoxin". This toxin breaks down the nerves of the human body causing thousands of electrical impulses to travel throughout the body. The effect causes intense perspiration, tears, and muscle spasms. If the patient is not treated promply the victim suffers brain damage and could easily go into a coma and die.

However there is an antivenom for both funnel-web bites. If bitten by either, immediate medical attention should be sought.