Venoms and poisons

Hold on for a moment, are spiders not Poisonous?

Indeed, that is correct! Spiders possess a distinct form of toxicity, utilizing a substance known as venom, which they inject into their prey or an unfortunate human who has startled them. It is important to distinguish between poisons and venoms based on a single factor: 

Poisons are ingested, absorbed, or inhaled and venoms are injected. 

For instance, rat poison is consumed by rats, leading to anticoagulation and internal bleeding, ultimately causing their demise. In contrast, venom is introduced into a living organism by passing the skin, affecting it in a different manner. Take, for instance, a bee sting, which introduces an acidic venom upon penetration through the skin, resulting in pain. Most venoms exert their effects on the body through the circulatory system or blood by interfering with the brain, heart, muscles, and nerves. However, there are a few highly toxic venoms, such as that of the funnel-web spider, which affects the body through the lymphatic system, but we will delve into this topic later when discussing antivenoms.

The key takeaway here is that venom is injected, while poison is ingested.

[image of funnelweb spider with venom][image of a poison]

Now, if all spiders possess venom, why are some more dangerous than others? 

The answer lies in the venom's toxicity. Toxicity is determined by numerous factors, including the mechanism of action, volume of venom, number of toxins, potency of toxins, and many others, which can become quite intricate. Nonetheless, the main point to remember is that only a few Australian spiders have medically significant venoms (e.g., redback and funnel-web spiders), while most others, such as huntsman spiders, wolf spiders, and orb spiders, are medically insignificant. Furthermore, the phrase "more or less venomous" is not the appropriate terminology; it is more accurate to say that a venom is more or less toxic. 

Adding to all the exceptions to keep up with, there is a genus of spider called Zosis sp. that is entirely non-venomous. These spiders are commonly found around and beneath houses and other sheltered dark spaces. However, it is advisable not to actively search for them, as their preferred habitat is also frequently occupied by redback spiders.

[image of zosis][image of redback spider][image of funnelweb]

But why does the body react to a spiders venom?

The majority of spider venoms primarily impact the body through the circulatory system. However, in highly toxic Australian spiders like funnel-web spiders, their venom enters and circulates within the body through the lymphatic system. Funnel-web venom contains δ-hexatoxins that target motor neurons by downregulating the inactivation of voltage-gated sodium ion channels (VGSCs).

The toxicity of a venom is also greatly influenced by external factors. For instance, each individual person possesses different blood compositions, particularly MHC II molecules, T helper type 2 responses, IgE production and generalised immune response. In most cases, individuals may experience mild discomfort, itchiness, swelling, and slight redness from an ant sting. However, in rare and extreme instances, a severe immune response known as a cytokine storm may occur, leading to a life-threatening anaphylactic attack characterized by extensive swelling throughout the body, often obstructing the airway. It is important to note that anaphylactic attacks from spider bites are among the least prevalent compared to a peanut allergy.

White tailed siders and other spider myths

The myth surrounding white-tailed spiders (Lampona cylindrata and Lampona murina) causing necrosis is a classic example of how misinformation can fuel rumours and misconceptions. While these spiders have often been associated with necrotic wounds, scientific evidence suggests that the cases of necrosis were not directly caused by the spiders themselves. Instead, it is believed that secondary infections, specifically necrotizing fasciitis, resulting from naturally occurring bacteria on the skin, were responsible for the severe tissue damage.

It's important to note that any species of spider could potentially introduce bacteria into a bite wound, leading to infection. However, due to a few isolated incidents where white-tailed spiders were found near necrotic wounds, they became erroneously blamed for causing the necrotic tissue. These incidents sparked a chain of misinformation and exaggerated claims about the spiders' venomous properties.

Additionally, it is worth debunking another common misconception regarding daddy long legs spiders. Daddy long legs, or harvestmen, are often mistakenly identified as spiders due to their similar appearance. However, they actually belong to a separate taxonomic group of arachnids. Harvestmen do not possess venom glands or fangs capable of biting through human skin. As a result, they are entirely harmless to humans and cannot cause any significant harm or toxicity.

Antivenoms and their use with Australian spider envenomation

Antivenom is a vital treatment for counteracting the effects of venomous spider bites, specifically those from Australian spiders like funnel-web spiders (genus Atrax and Hadronyche). Funnel-web spiders are known for their potent venom, which can cause severe symptoms and even be life-threatening. Antivenom, also called antivenin or antivenom serum, is a species-specific antitoxin produced by injecting small amounts of spider venom into controlled animals (often horses or sheep). The animal's immune system generates antibodies against the venom, which are then purified from the animal's blood. These antibodies are used to create the antivenom.

The antivenom antibodies bind to and neutralize the venom's toxins. When administered to a bite victim, they prevent the venom components from interacting with the victim's cells, reducing harm. Antivenom is primarily given through intravenous infusion and is most effective when administered promptly after a spider bite.

Australian funnel-web spiders and their potentially lethal venom make antivenom an essential part of spider bite management in Australia. Its development and production involve extensive research, laboratory testing, and clinical trials. Antivenom is manufactured by specialized facilities with the necessary expertise, facilities, and regulatory approvals. For Australian funnel-web spiders, venom is collected from captive spiders and processed to remove impurities. The venom is then used to immunize animals, which receive increasing doses over time, stimulating a robust antibody response. Plasma containing specific antibodies against the spider's venom is separated and processed to create the antivenom.