A friend on Facebook asked: "how many of those deaths have actually been recorded to be attributed to wild animal attacks like Poisonous snakes or alligator attacks? One would think this would be a fairly substantial number with most of the fighting happening in the Southern states and eastern mountain ranges where such critters are numerous."
Thanks for any help guys!
I didn't know this offhand but it's a fun question to research.
Weirdly, animals do not like giant groups of humans and tend to stay away. According to Laurence Klauber in Rattlesnakes: Their Habits, Life Histories and Influence on Mankind (1956):
"...The medical statistics of the Civil War do not disclose a single death from snake bite on the Northern side... At army camps in the United States during World War II (years 1942 to 1945 inclusive) there were 1,910 hospital admissions for bites or stings of venomous animals, including, of course, rattlesnake bites. This was at the rate of one man out of every 10,000 exposed. There were no fatalities. This entailed nearly 20 million man-years of exposure, many of which were spent in the rattlesnake-infested areas of the Southwest."
Kelby Ouchley's Flora and Fauna of the Civil War: An Environmental Reference Guide contains a lot of fun primary quotes.
Captain Charles B. Haydon of the 2nd Michigan Infantry wrote home on June 27, 1863: "The alligators eat some soliders but if the soldiers would keep out of the river they would not be eaten." Despite that testimony, I couldn't find any records of any fatal alligator attacks, or attacks by wolves, bears, or mountain lions.
Did it occur? I'd be shocked if a handful of men weren't killed by wild animals during the war, recorded as missing. A wounded man, praying for relief on the field of battle or crawling for refuge into a swamp, must have found claw and tooth instead. But we're talking a vanishingly small number.
Horses and mules were a much greater threat: Generals Grant, Lee, and Jackson were all injured when thrown from their horses. The Confederate Brig. Gen William E. Baldwin was killed when his stirrup broke. The Union's Brig. Gen Michael Corcoran was crushed to death when his horse fell on him. A lot of accidental deaths during the war can be attributed to attacks by domestic animals.
Of course, the most deadly (non-human) animal of the Civil War was the mosquito, which infected over two million Union and Confederate soldiers with malaria.