Fish, snakes, and spiders are often
described as either being venomous or poisonous. The difference is
in the delivery system. Those that are venomous inject their
target with their toxin through a bite, sting, or sharp body
protrusion. Those that are poisonous have toxins that must be
swallowed or inhaled in order to be dangerous.
Venomous animals need to get their toxins beneath the skin and
then into the bloodstream to be effective. Some have a venomous
bite, but are safe to eat. Many caterpillars have defensive venom
glands associated with specialized bristles, known as urticating
hairs, which can be lethal to humans. There are about six venomous
snake and about seven venomous spider fatalities in the US each
year. Venoms are usually not lethal if swallowed.
Poisonous fish can be potentially deadly if eaten. Poisons work
mostly through the digestive system and mucous membranes of the
body. Some poisons can be transferred easily to humans by merely
touching or handling.
The yellow-bellied sea snake has both a venomous bite and
poisonous flesh.
There are several types of venom. Neurotoxins attack the brain and
the nerves. Animals whose bite results in paralysis use this type
of venom. Cytotoxins are a type of venom that causes the most
pain, as this venom attacks cells directly, causing them to
rupture and release their contents into the body. Hemotoxins
attack blood cells directly and most kill red blood cells, which
interrupts the flow of oxygen throughout the body. Not all
poisonous or venomous creatures are fatal to humans, but they
are all discomforting.