Passive
Poisoners Any poisonous species that requires an action by the target organism to dispense its poison is called
a passive poisoner. Virtually all plants that produce toxic secondary substances are passive
poisoners because they must be ingested in order for their poisons to have an effect. The addictive alkaloid drugsÑsuch as nicotine from tobacco, cocaine from the coca plants, opium from poppies, psilocybin from certain mushrooms, and tetrahydrocannabinol from the marijuana plantÑbelong in this category. Castor beans (Ricinus communis) and oleander foliage (Nerium oleander) are other examples of passive poisons.
Some animals are passive poisoners. Puffer fishes in the family Tetrodonidae are considered a delicacy in Japan and southeast Asia, although the viscera of these fish contain tetrodoxin, an extremely potent poison. Japanese cooks are specially trained and licensed to prepare fugu using this fish; nevertheless, there are more than 150 fatalities each year due to puffer-fish poisoning.
Other types of passive poisoners that require only animal contact in order to transmit poison include poison oak, poison ivy, and poison sumac, and the skin of bufonid toads, Bufo, which all exude toxic substances that cause irritation of the epidermal tissues of animals that contact them. Certain Central and South American tree frogs produce a poison from skin glands whose toxicity is so severe that small amounts are used to tip darts and arrows for hunting. An additional example of passive poisoning is found in blister
beetles in the family Meloidae; when the beetles are molested, they leak their hemolymph (insect blood), which contains the extremely irritating toxin cantharidin, from their leg joints. Cantharidin is used as a skin irritant to remove warts.
Some poisonous plants and animals that use passive poisoning either to secure prey or for defense deliver their noxious chemicals when an offending animal punctures itself with sharp spines or triggers an otherwise static delivery mechanism. In nettles tiny spinose hairs inject the plant's poison, as do the urticating (stinging) hairs of certain caterpillars. Lion fish and scorpion fish in the family Scorpaenidae are some of the most venomous fish; if approached in a contentious manner, they present their venomous spines and invite the aggressor to bump them. Coelenterates such as jellyfish, sea anemones, and stinging corals have tiny barbed darts called nematocysts, which inject venoms when triggered by contact. The sting of the large colonial coelenterate known as the Portuguese man-of-war, Physalis, causes intense burning sensations; although the severe pain lasts for hours, the sting is rarely fatal.
Active Poisoners
The overwhelming majority of venomous animals are active poisoners, with aggressive behavior patterns or mechanisms specifically evolved to dynamically deliver their venoms. Active poisoners employ three basic methods of dispensing their venoms: biting, stinging, and squirting. Biting includes piercing, stabbing, and chewing. Piercing involves highly specialized mouthparts through which sharp stylets pierce the skin of the victim; these parts are found in the insect orders Hemiptera (the true bugs) and Diptera (the flies). Salivary or associated glands produce the venom, and ducts transport it to the tubelike mouthparts through which it is injected into the victim. Stabbers include all hollow-fanged species such as spiders, centipedes, and rattlesnakes. These creatures employ hypodermic injection directly analogous to what is accomplished by a hypodermic needle and syringe. A few species, including the Gila monster, Heloderma suspectum, and some hind-fang snakes, release their venom into a wound inflicted by their chewing on the victim's flesh.
Stinging species that are active poisoners include the sting rays, the scorpions, and the ants, wasps, and bees in the insect order Hymenoptera. The barb at the tip of the scorpion tail injects venom prduced in the last tail segment. Ants, wasps, and bees have posterior abdominal stingers that are hollow. These inject venom from special glands and storage sacks in the abdomen. This apparatus is most highly developed in the honeybee Apis melifora, where it is used mainly for defense against vertebrates. The honeybee sting is barbed, and the entire venom delivery system detaches from the bee's body when the stinger is anchored in vertebrate tissue; a bee can sting only once and dies in the process.
Venom squirters are a remarkable group that includes whipscorpions, Uropygi, that spray acetic acid on their antagonists, and the bombardier beetles, Brachinus, that create a small explosion in a specially designed abdominal chamber such that a caustic liquid at a very high temperature blasts from the insect's posterior. Darkling beetles, Eleodes, stand on their heads and squirt a mixture of quinones from a posterior opening when disturbed. The marksmanship of the spitting cobra, Naja nigricollis, is such that it can project its venom up to 3 m (9.8 ft) and hit the eyes of its victim. This feat is surpassed by skunks, Mephitis, which can disable enemies up to 9 m (30 ft) away with a fine spray of butyl mercaptan.