THE STORY GOES LIKE THIS
One important feature of the event is that there were no eyewitnesses to the snakes actually falling with the rain. They were there alright, at ground level, but none were found on rooftops, in cisterns or any other elevated areas. And in the Monthly Weather Report it is stated that "Vance Street is comparatively new, has no pavements, gutters merely trenches"
After the Ledger published their account, the story hit the newswire where it was picked up by the New York Times (see picture above) and the Scientific American Supplement. Scientific American considered a hurricane as a possible explanation for the snakes, but remained puzzled as to where such a large collection of snakes could have been taken from.
Charles Fort rightly points out that a hurricane of such magnitude as capable of scooping up thousands of snakes would likely have deposited other debris such as twigs and leaves. Also, snakes are dormant in January, like other reptiles, their cold-blooded nature leaves them with no source of warmth during the winter months so they usually gather in a burrow or hibernacula until the weather turns again. A typical hibernaculum will have as many as a hundred snakes in it, but to find one with thousands in it is extremely rare.
It should also be noted that Memphis has never experienced a hurricane because it is too far away from sea. A severe derecho with hurricane force winds blasted through Memphis in 2003 and was known by locals as "Hurricane Elvis". Hurricane Elvis left hundreds of thousands of homes without power and killed seven people, dwarfing the 15-minute downpour preposterously. In other words: it wasn't a hurricane.
Well what was it then? Charles Fort believed that the snakes had traveled to earth on warm air currents from outer space. But we can assume that the snakes didn't actually fall from the sky because there were no witnesses to that and the snakes were mostly, if not all alive and uninjured on the ground. So if they didn't come from the sky, can we assume they came up from under the ground?
It's an elegant solution to the problem but snakes don't behave that way. They stay in their hibernaculum until it's time for their snake orgies and summer barbecues. So, what kind of creature does come up from the ground after a hard and heavy rain? (Even a bird would know the answer to this one ...)
It seems that the larvae of horsehair worms are parasitic. They live off of arthropods such as large insects and shellfish. They are free moving in their mature form. When exposed to water mature worms will exit the host and apparently, in this instance, had nowhere else to go but up.
And that's that!
Not quite. As is often the case when confronted with the mysterious, the university scientist(s) seem to have rushed to an easy conclusion. How can two whole city blocks worth of people misidentify horsehair thin parasitic worms for snakes? It's possible, but you'd figure someone would be able to spot the difference. What's more, horsehair worms don't behave in the ways described by witnesses, if they're to be believed.
So if it wasn't snakes and it wasn't worms, then what was it? Little believed it was leeches taken by a waterspout from a lake of the Mississippi River. It's the same opinion that was taken by the editor of the original Public Ledger article way back in 1877.
Monthly weather report to House of Representatives for 2nd session of the 45th congress, 1877-78
or this alternate link
Unnatural Phenomena: A Guide to the Bizarre Wonders of North America
On This Day in Memphis History
The Complete Books of Charles Fort pgs. 93-4
*Note: Even though two different versions are available online I couldn't find the original Scientific American article from February 10, 1877 in the table of contents or perusing the actual content which led me to believe that either the event was simply mentioned in an article about some other thing or that the version I read through is incomplete. Here it is.