Reptile & Amphibian Forums

I'm kinda new to understanding venomous snakes...and I was just trying to understand the whole LD50 thing. What does the LD50 stand for? My guess is that the milligrams (i.e. LD50 0.14 mg) means that it would take 0.14 milligrams to kill something...I'm just not sure what. So if anyone could shed some light on this, I'd appreciate it.

Its leathal dose 50. That means how much it takes to kill 50% of mice its injected into. I think its in milligrams but Im not sure. Basically, the lower the LD50, the more toxic the substance.

50% of a single mouse (i.e. the mice being half-way dead) or 50% of a group of mice (i.e. killing 6 out of 12)?

50% of a group. I think its actually 50 out of 100 mice.

Yes, it's the amount of venom required to kill P of a group of mice (in 24 hours I believe). I don't think there's a specific number of mice required for the test (but of course, the more one used the more accurate the result). Units are normally given in milligrams per kilogram, in other words, how many milligrams of (dried) venom it takes to kill P out of 1 killogram of mice (1 kg is about 30-40 mice, I don't remember if there a specific size of mouse for the test, but probably).

Remember not to go by LD50 alone when judging how dangerous a snake is. At the very least, you should consider LD50 and the average venom yield for the species. Divide the venom yield in mg by the LD50 in mg and you'll get the number of kilograms of mice that a single bite will kill (P of that actually) which is a much more useful number in comparing species. Unfortunately, it's sometimes hard to find both of these numbers for some species, and the numbers that ARE published sometimes vary significantly from one source to another.

Also keep in mind that there is a fair amount of debate (and very little hard information) about how well the LD50 in mice parallels the venom's potency against humans...sice obviously people aren't lining up to have snake venom injected into them to see how much it takes to kill them.

The NEW LD50 numbers, as tested on humans!

The other problem is variance in venom yield. If the snake holds on and continues injecting, you could be in a lot more trouble. I also heard about an experiment stating baby rattlers inject more venom but take longer to kill a rodent. It was stating that they inject more of a less potent venom, and the venom becomes more toxic as they grow older. Then they inject less venom but are more dangerous as an adult.