A Western Diamond-Backed Rattlesnake in a Commercial Facility in San Antonio, Texas

— This article by Jerry Cates and Martha D., first published on 2 April 2010, was last revised on 24 April 2016. © Bugsinthenews Vol. 11:04(01).


Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Lateral Head, with Fangs Extended

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Lateral Head, with Fangs Extended

This 17-inch-long, juvenile Western Diamond-backed Rattlesnake was observed by a sharp-eyed night shift supervisor at a commercial facility in San Antonio. The supervisor, a woman, was walking down a well-lighted hallway–at midnight–when she saw what she thought was a snake’s head peering out from under the locked doorway to an office. The office’s occupant, who worked the 9-5 shift, was not in at the time.


—Note: all the photographs on this post can be enlarged for better viewing by moving your cursor over them and left-clicking the photo—


She watched the door for a few more seconds. When the head appeared a second time, she decided it was time to call in the facility maintenance supervisor. He arrived a few minutes later, opened the door to the office, and found the snake on the floor near the door, very much alive. But not for long

NOTE: Statistics on snake bites consistently show that the general danger involved pales when compared with other, more common risks, such as automobile accidents or even lightning strikes. Nevertheless, a Western Diamond-backed rattlesnake, loose in a building occupied by humans, clearly poses a health hazard. The bite of one of these serpents, if accompanied by envenomation (estimates for venomous snake bites that are wholly or partially ineffective head-butts or dry bites range from 25-50%, depending on the source), can be life-threatening. Even a non-life-threatening bite can result in extensive tissue loss, lengthy recuperation and rehabilitation, and well over $10,000 in medical bills (sources in Sweetwater, Texas, claim a serious rattlesnake bite will sometimes result in medical bills exceeding $100,000, and in today’s economy some authorities suggest such costs range from $50,000 to $150,000, particularly if plastic surgery is required).  And serpent size is no indication of risk, as juvenile rattlesnakes generally pose as serious a threat as a mature specimen. Since the potential risks to human life and limb are significant, they must be taken seriously, and–when lacking professional herpetological containers and handling tools, and extensive training in their use–it is reasonable for those in authority to apply decisive force to end the threat quickly and finally…

The maintenance supervisor struck the snake on its neck with a blunt object. This  broke its back (all snakes have very fragile spines, especially in the upper third of the body within inches of where the head joins the neck) and killed it. However, although a snake may be technically dead, it can continue to bite and (if venomous, as this was) inject venom for several hours. Knowing this, he carefully placed the snake’s body in a closed, rigid container, to be analyzed by a herpetologist in the morning. Next, he searched the office carefully, looking for additional snakes. Finding none, he then inspected for places where the snake may have entered the building. In the process, he discovered that the office’s wall unit air-conditioner had a 1/4th-inch gap, underneath, through which a snake might be able to enter the room from the yard, outside. He caulked this gap thoroughly, inside and out, and called it a night.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas: Martha--Dorsal Body

Western Diamond-backed Rattlesnake (Crotalus atrox), 04.01.10, San Antonio, Texas–Dorsal Body

The next morning, at 8:39 A.M., I received a call requesting my presence at the facility. The maintenance supervisor wanted advice on how to make sure there were no additional snakes in the facility grounds. He also wanted advice on how to avoid this problem in the future.

A nagging question in my mind had to do with whether the snake had entered through a wall opening (from the yard), or via a drain (from the sewer). My experiences suggested that, with the exception of snakes in the genus Elaphe and a few others, most serpents–and this is particularly true of rattlesnakes at the end of winter hibernation–enter structures via a sewer connection. Such incidents (finding a snake inside a residential structure) are exceedingly rare, but when they occur and the snake is clearly not a rat snake (which often enter homes by following a rodent or its trail), they are most often found in bathrooms. In most residential structures, the typical route of ingress is via the commode.

When asked if the office where the snake had been found contained any sinks, the maintenance supervisor replied that a single sink was in the room. However, that sink had a fine steel grate that the snake would not have  been able to navigate through.

After rearranging the day’s schedule, I drove to San Antonio that afternoon. The snake’s carcass was in excellent condition, which is unusual. Normally, when a red-blooded American — especially a Texan — kills a venomous snake, the head gets mashed to smithereens. Not so with this specimen. The head was intact in all particulars, and showed no outward signs of trauma. All parts of the body could be examined thoroughly.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas: Martha--Tail, with Rattles

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas: Martha–Tail, with Rattles

The tail, which had the white and black “coon-tail” banding typical of the Western Diamond-backed rattlesnake, had two rattles and a pre-rattle on its terminus. The photo at left appears, at first, to show four rattles. However, the two-segmented structure on the distal end is actually a single, bell-shaped rattle that is shaped just like the rattles behind it.

The terminal structures of rattles 2 and 3, however, are hidden, being ensconced within the interior recesses of the next rattle in line. Rattle 3, the proximal “pre-rattle”, isn’t quite a rattle yet. It won’t be accorded that distinction until the next molt.

The Western Diamond-backed rattlesnake is born with a pre-button that is shaped like a tiny helmet, like those worn by the Allies in WW-I. This pre-button is lost during the first ecdysis (skin shed), and is replaced with a terminal button like the one seen at the end of this snake’s tail. As mentioned earlier, each rattle is shaped like this button, but you cannot readily see the full extent of any but the last button on the rattle.

What the two extra rattles mean, of course, is that this snake has shed its skin at least twice since emerging from its mother, either in late summer or early fall of 2009.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Rattles

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Rattles

Western Diamond-backed Rattlesnakes are ovoviviparous, that is, the female fertilizes her eggs in the ovaries with sperm from a mating that may have occurred months earlier, and these eggs are then sheathed with a thin, leathery covering that protects them as the embryos develop; the egg yolk supplies the only nourishment needed until birth occurs, and that takes place either inside the female’s body or just after she lays them. The female gives birth to (a litter of 4-25) live snakes. They mate in the springtime, sometime between the beginning of March and the end of May.

This serpent could have shed more than twice, and some of the rattles thus produced could have been lost in combat or by getting caught in the landscape as the snake traveled about. That, in fact, happens so often to mature rattlesnakes in the wild that it is rare to see a mature specimen with more than 7-9 rattles. However, a loss of rattles seems unlikely, owing to the small size of this specimen, and the paucity of food characteristic of most hibernacula, where these snakes spend the winter months.

Ecdysis, or the shedding of an old skin in favor of a new one, is regularly carried out by serpents in response to a single variable–namely, food intake. The more often, and lavishly, a serpent eats, the more often it sheds its skin.

Lean times in the food department for serpents of all kinds, in the wild, have characterized the past two years in Texas. A protracted drought–that only recently came to an end–significantly reduced the quality and quantity of wild meadowland grasses. That led to a corresponding reduction in rodent populations, which depend on grass seed to survive. Inasmuch as rodents supply the bulk of ophidian dietary requirements, the likelihood that this serpent might have had more than two molts since birth seems rather remote.

If you click on the above micrograph of the rattles, to see its larger version, you will notice that the faint outline of the hidden portion of the  second rattle shows through the translucent shell of the first (terminal) rattle. A fully-formed rattle is made of lifeless chitinous matter, which is neither innervated or supplied with blood. Notice, by contrast, that the third, or pre-rattle, is colored a pale white. This structure is alive, with both nerves and blood vessels. When the snake goes through its next ecdysis event, this pre-rattle will lose those connections and revert to a lifeless shell, which is required to enable it to make the special sound, known the world over as that of a rattlesnake, when the tail is vibrated.
Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Fang

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Fang

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Fang, Line Drawing, Annotated

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Fang

Under the microscope, the two fangs of this specimen provided some interesting clues regarding where the serpent had spent its final hours. Neither fang appeared to be doubled with a replacement, though such doublings are common with this species as the old fang nears the last 5-6 days of its useful life (6 to 10 weeks [3]). The fang on the left side of the head was clearly damaged at its distal end: its point was shattered, as if forcibly struck against a hard, unyielding surface. The fang on the right side, shown in the microgram at left, was intact, and measured 6-7 mm, from tip to root.

If the micrograph at left is enlarged, it is possible to see the venom egress (injection) port in the distal anterior medial surface. This egress port (which Klauber calls a “discharge orifice” [4]) has the shape of an elliptical slot aligned with the long axis of the fang. As Klauber points out, the injection port is not at the distal end of the fang, and thus can be blocked by heavy leather, and absorbed, harmlessly, by cloth. In this case, the venom egress port terminated more than 1 mm from the tip (compare the morphology of the fang of a mygalomorph spider, from Kempner, Texas). In experiments conducted with a large Western Diamond-backed rattlesnake, Klauber [5] showed that the leather of a man’s oxford shoe could not be penetrated by the snake’s fangs, even in a forceful strike.  These points suggest that most heavy boots, particularly those that protect the leg up to 12-18 inches from the heel, offer excellent protection against snake bite from most snakes. Klauber suggests, however, that one should consider fortifying one’s protective gear as much as possible.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Exposed Body Cavity, Annotated

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Exposed Body Cavity, Annotated

One way to determine where this snake had spent the hours previous to its death is to perform a dissection to examine the contents of its stomach. On returning to the lab from the site in San Antonio, such a dissection was carried out.It was hoped that fauna would be found in the stomach contents that was suggestive of specific locales. For example, finding a smoky brown cockroach (Periplaneta fuliginosa) would indicate an outdoors habitat, while finding an American cockroach (Periplaneta americana) would favor the environs of a public sewer. The dissection was inconclusive, however, as the stomach was essentially empty.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas--Utility Room Drain

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Utility Room Drain

Despite the lack of clear evidence pointing one way or the other, circumstances seem to indicate that this serpent entered the building from the sewer rather than from the yard.

On inspecting the room where the snake was discovered, a floor drain–in an attached closet that was only accessible via a doorway into the room–was found. This drain was covered by a brass grate with slots measuring up to 1.25 inches x 0.25 inches, through which this snake could easily have navigated. A careful examination of this grate shows that, although debris occludes some of the slots,  several that are sufficient for a snake of this size to pass through are clean and unobstructed.

The timing of this incident coincided with the annual emergence of snakes from their winter hibernacula, where the food supply might be quite sparse. Many snakes take up residence in sewers to hibernate during the winter months, and the water in a p-trap, such as that found in the distal reaches of this drain, would not deter a snake seeking a way out of its winter hideaway.

On the other hand, it seems relatively unlikely that a Western Diamond-backed rattlesnake would find the yard of this commercial facility inviting. A thorough inspection of the grounds showed that the grass was well-kept, and mowed to less than 1.5 inches. There were no open drains, or any other potential harborage for snakes within 100 feet of the exterior wall of the subject office.

My recommendation to this facility, therefore, was that maintenance personnel should take steps to seal the floor drains–particularly those in closets normally kept closed and dark–with 0.25 inch mesh hardware cloth. Snakes cannot navigate through such materials, but–since the flow of water is not impeded (if the sealing is done properly) the integrity of the drain is not compromised.



Questions? Corrections? Comments? BUG ME RIGHT NOW! Feel free to e-mail jerry.cates@entomobiotics.com. You may also leave a comment in the space provided below.

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