why do some snakes have stronger venom than others?

Answer 1

Evolution, it all depends on their diet and surroudings

Answer 2

Snake venom is one of the most amazing and unique adaptions of animal evolution. Venomous serpents have developed one of the most effective and efficient weapon systems of the animal kingdom. What is snake venom and how does it work? Venom is a prey-immobilizing substance in snakes that is used secondarily as a defense system. Venom is not composed of a single substance, but is a toxic saliva consisting of a complex mixture of chemicals called enzymes. Almost all venoms are composed of approximately 90% proteins. Two general types of toxins are known, neurotoxins and hemotoxins. Neurotoxic venom attacks the victim's central nervous system and usually result in heart failure and/or breathing difficulties. Cobras, mambas, sea snakes, kraits and coral snakes are examples of snakes that contain mainly neurotoxic venom. Hemotoxic venom attacks the circulatory system and muscle tissue causing excessive scarring, gangrene, permanent disuse of motor skills, and sometimes leads to amputation of the affected area. The Viperidae family such as rattlesnakes, copperheads, and cottomouths are good examples of snakes that employ mostly hemotoxic venom. Some snakes contain venom that contains combinations of both neurotoxins and hemotoxins.
There are approximately 20 types of toxic enzymes found in snake poisons throughout the world known to man. Although no venomous snake has all of these toxins, most snakes employ between six to twelve of these enzymes in their venom. Each of these enzymes has its own special function. Some aid in the digestive process, while others specialize in paralizing the prey. Scientists believe they have identified the following chemicals from snake venom and the specific purpose of each as follows:

cholinesterase; attacks the nervous system, relaxing muscles to the point where the victim has very little control.
amino acid oxidase; plays a part in digestion and the triggering of other enzymes, (is responsible for venom's characteristic light yellowish coloring.)
hyaluronidase; causes other enzymes to be absorbed more rapidly by the victim.
proteinase; plays a large part in the digestive process, breaking down tissues at an accelerated rate. (causes extensive tissue damage in human victims)
adenosine triphosphatase; believed to be one of the central agents resulting in the shock of the victim and immobilizing smaller prey. (probably present in most snakes.)
phosphodiesterase; accounts for the negative cardiac reactions in victims, most notably a rapid drop in blood pressure.
These are only a few of the enzymes found in the chemistry of snake venom known today. Other enzymes have been isolated and identified but their purpose is still largely a mystery to science.
Now that you probably feel that you have just taken a crash course in organic chemistry, you probably want to know if science has made any progress in finding within this new-found knowledge of venom any benefits for humans. Although the danger of snake venom to humans has been well documented, mankind also benefits from increased research of snake venom. The most obvious benefit to man is the snake venom's role in producing "antivenom" (also known as "antivenin") to help counteract the effects of snake bites. The most well-known method of producing antivenom is a technique referred to by many as the "horse serum" method. Venom is injected into the horse, slowly increasing the amount as the horse builds up antibodies to the venom. Blood is then taken from the animal and the serum containing the antibodies is then separated. Unfortunately about one-third of all recipients have allergic reactions to horse serum. Standard procedure calls for a test for serum sensitivity before giving antivenom to patients. Although certain "polyvalent" antivenoms can be utilized for certain "groups" of snakes, usually each type of snake has its own specific antivenom.

Besides the obvious benefits of snake venom to produce antivenom, have there been any other breakthroughs in medical research? There have been many early results from research that gives promise on many medical fronts. In France, an enzyme derived from copperhead venom may hold an answer to treatment for breast cancer. Ingredients from the venom of a Malayan pit viper has shown promise in breaking blood clots that would be very beneficial in treating stroke victims. Enzymes from cobra venom may hold the keys to finding cures for Parkinson's disease and Alzheimer's disease. Some viper venom seems to hold the secrets to curing osteoporosis and promoting tumor reduction. Several venom extracts have shown possibilities that could lead to the production of anticoagulants that would be helpful in treating heart disease. Proteins from certain rattlesnakes has produced blood pressure medicine. Ingredients from the red-necked spitting cobra has provided clues to breaking down cell membranes that would provide treatment for leukemia and cancer. It is obvious that these very complex enzymes derived from snake venom could produce potentially huge medical benefits for mankind. Besides protecting these unique creatures as part of a responsible effort to preserve our natural heritage, it seems increasingly clear that protecting venomous snakes is in our own best medical and health interest.