What Is the Difference Between Venomous and Poisonous?

Venoms are delivered actively, while poisons are released passively

Black widow spider
stephanie phillips / Getty Images

The terms "venomous" and "poisonous" are often used interchangeably to refer to toxic substances produced by animals and their dangers to humans and other creatures, but they have different meanings in biology. Basically, venoms are delivered actively while poisons are delivered passively.

Venomous Organisms

A venom is a secretion that an animal produces in a gland for the purpose of injecting it into another animal. It is actively introduced into a victim by means of a specialized apparatus. Venomous organisms use a wide variety of tools to inject venom: barbs, beaks, fangs or modified teeth, harpoons, nematocysts (found in jellyfish tentacles), pincers, proboscises, spines, sprays, spurs, and stingers.

Animal venoms are generally a mix of proteins and peptides, and their precise chemical makeup to a large extent depends on the purpose of the venom. Venoms are used for defense against other creatures or for hunting prey. Those used for defense are designed to create immediate, localized pain to make another animal go away. The chemistry of venoms designed for hunting prey, on the other hand, is highly variable, since these venoms are made specifically to kill, incapacitate, or break down the victim's chemistry to make it easily edible. If cornered, many hunters will use their venom for defense.

Glands and 'Hypodermic Needles'

The glands where venoms are stored have a ready supply of venom and a muscular arrangement to eject the toxic substance, which can affect the rapidity and degree of envenomation. The reaction in the victim is principally determined by the chemistry, potency, and volume of the venom.

Most animal venoms are ineffectual if the venom is merely placed on the skin or even ingested. Venom requires a wound to deliver its molecules to its victims. One sophisticated apparatus for creating such a wound is the hypodermic syringe-style mechanism of ants, bees, and wasps: In fact, inventor Alexander Wood is said to have modeled his syringe on bee sting mechanisms.

Venomous Arthropods

Venomous insects can be divided into three groups: true bugs (order Hemiptera), butterflies and moths (order Lepidoptera), and ants, bees, and wasps (order Hymenoptera). Here's how the venom is delivered:

Poisonous Organisms

Poisonous organisms don't deliver their toxins directly; rather, the toxins are induced passively. A poisonous organism's entire body, or large parts of it, might contain the poisonous substance, and the poison is often created by the animal's specialized diet. Unlike venoms, poisons are contact toxins, which are harmful when eaten or touched. Humans and other creatures can suffer when they come in direct contact with or inhale airborne material from urticating (stinging nettle-like) hairs, wing scales, molted animal parts, feces, silk, and other secretions.

Poisonous secretions are almost always defensive in nature. Those that aren't defensive are simple allergens that have nothing to do with defense. A creature can come in contact with these secretions even after a poisonous organism is dead. The defensive contact chemicals produced by poisonous insects can cause severe local pain, local swelling, swelling of the lymph nodes, headache, shock-like symptoms, and convulsions, as well as dermatitis, rashes, and upper respiratory tract complications.

Poisonous Arthropods

Poisonous insects include members of quite a few groups: butterflies and moths (order Lepidoptera), true bugs (order Hemiptera), beetles (order Coleoptera), grasshoppers (order Orthoptera), and others. Stinging caterpillars use barbed spines or hairs as defensive mechanisms, while blister beetles produce a caustic chemical when they are threatened.

Here's how some insects produce their poison:

  • Monarch butterflies develop a defensive flavor by eating milkweeds, and birds that eat them eat only one.
  • Heliconius butterflies have similar defensive poisons in their systems.
  • Cinnabar moths feed on poisonous ragworts and inherit the poison.
  • Lygaeid bugs feed on milkweed and oleander.

Which Is More Dangerous?

Venomous black widow spider bites, snake bites, and jellyfish stings certainly sound more dangerous than contact poisons, but in terms of worldwide exposure, the more dangerous of the two is undoubtedly animal poison, since it doesn't require animals to take an active role in the toxin delivery system.

Sources