Part 2

TABLE 1.--Frequency of Occurrence of Various Numbers of Supralabial and Infralabial Scales in 102 Cottonmouths.

==================================================== | |Specimens |Specimens | | | |Number |having |having |Total |Percentage | |of scales |number on |number on | | | | |both sides |one side | | | |----------------------------------------------------| | Supralabials | |----------------------------------------------------| | 7 | 11 | 24 | 35 | 25.2 | | 8 | 64 | 27 | 91 | 65.5 | | 9 | 0 | 3 | 3 | 2.2 | |----------------------------------------------------| | Infralabials | |----------------------------------------------------| | 8 | 0 | 2 | 2 | 1.5 | | 9 | 3 | 10 | 13 | 9.6 | | 10 | 12 | 32 | 44 | 32.4 | | 11 | 53 | 22 | 75 | 55.1 | | 12 | 0 | 2 | 2 | 1.5 | ----------------------------------------------------

TABLE 2.--Numbers of Supralabials and Infralabials of 102 Cottonmouths.

=========================================== | Number of | Number of | Number of | | individuals | supralabials | infralabials | | 37 | 8 | 11 | | 15 | 8 | 10-11 | | 12 | 7-8 | 11 | | 6 | 7-8 | 10-11 | | 5 | 8 | 10 | | 5 | 8 | 9-10 | | 4 | 7 | 11 | | 3 | 7 | 9-10 | | 3 | 7-8 | 10 | | 2 | 7 | 9 | | 2 | 7 | 10 | | 2 | 8 | 10-12 | | 2 | 8-9 | 10 | | 2 | 7-8 | 8-9 | | 1 | 7-8 | 9 | | 1 | 8-9 | 10-11 | -------------------------------------------

The dorsal scales of cottonmouths are strongly keeled except that those of the two lower scale-rows on each side are weakly keeled. Also they are slightly larger than the others. Two apical pits are present on each dorsal scale. The shape of the scales and number of scale rows vary depending upon the position on the body. Scales on the neck are considerably smaller than those elsewhere on the body and are arranged in two or three more rows than those at mid-body. The skin in the region of the throat, neck, and fore-body is especially elastic and allows the swallowing of large prey. Posteriorly from the mid-body the scales decrease in size and become more angular, those on the tail tending to be rhomboidal and wider than long. In the region of the anus the number of scale rows diminishes rapidly, leaving only 12 to 14 rows at the base of the tail and only three rows immediately ahead of the tail tip. The tail ends in a spine composed of two scales: one scale covers the bottom, lower parts of the sides, and tip of the spine; and a shorter dorsal scale covers the top and upper parts of the sides of the basal two-thirds of the spine. The spine of embryos and young cottonmouths is blunt, but is pointed in most adults.

TABLE 3.--Variation in Numbers of Supralabials and Infralabials in a Brood of Seven Cottonmouths.

=========================================== | Number of | Number of | Number of | | individuals | supralabials | infralabials | | 1 | 7 | 9 | | 1 | 7 | 9-10 | | 2 | 7-8 | 8-9 | | 1 | 7-8 | 9 | | 1 | 8 | 9-10 | | 1 | 8-9 | 10 | -------------------------------------------

TABLE 4.--Analysis of Number of Scale Rows at Three Parts of the Body in 81 Cottonmouths.

============================================================== | | Neck | Mid-body | Anterior to anus| | |--------+--------+--------+--------+--------+--------| | Number | Number | Per- | Number | Per- | Number | Per- | | of | of |centage | of |centage | of |centage | | scales |indivi- | |indivi- | |indivi- | | |per row | duals | | duals | | duals | | |--------+--------+--------+--------+--------+--------+--------| | 29 | 1 | 1.2 | ... | ... | ... | ... | | 28 | 3 | 3.7 | ... | ... | ... | ... | | 27 | 52 | 64.2 | ... | ... | ... | ... | | 26 | 16 | 18.0 | 2 | 2.5 | ... | ... | | 25 | 8 | 9.9 | 67 | 82.7 | ... | ... | | 24 | 1 | 1.2 | 4 | 4.9 | ... | ... | | 23 | ... | ... | 8 | 9.9 | 4 | 4.9 | | 22 | ... | ... | ... | ... | 4 | 4.9 | | 21 | ... | ... | ... | ... | 68 | 84.0 | | 20 | ... | ... | ... | ... | 5 | 6.2 | --------------------------------------------------------------

The number of scale rows on the neck, at mid-body, and just anterior to the anus is relatively constant at 27-25-21, respectively; but some individual variation is evident (Table 4). Since the rows are diagonally arranged, it is necessary in counting scales to proceed either anteriorly or posteriorly across the back; or the row may be counted in either direction up to the center of the back and then reversed on the other side of the snake. In order to count the scale rows in a position where no scale reduction or addition was occurring and to avoid as much error as possible, I counted from anterior to center and back on the neck, in any direction at mid-body, and from posterior to center and back near the anus. Because females generally are the larger in circumference posteriorly, they could have more scale rows than males just anterior to the anus. The few snakes having more than 21 scale rows in the posterior region offer no conclusive evidence as to tendencies, but in both instances in which this occurred the females outnumbered the males three to one. An odd, rather than an even, number of scale rows occurs on most of the length of the snakes examined, because there is a mid-dorsal row and scale rows tend to be lost on both sides at about the same level. An example of scale reduction of one snake was as follows:

6+7 (13) 6+7 (96) 27 -------- 25 -------- 24 -------- 23 --------- 22 --------- 5+6 (13) 5+6 (90) 7+8 (111) 7+8 (114)

6+7 (122) +7, -5 (125) 23 -------- 22 -------- 23 --------- 21 -------- 22 ------------ -6 (118) +6 (119) 6+7 (121) +6 (123)

-6 (126) 22 -------- 21 (130).

This scale reduction follows the method proposed by Dowling (1951b: 133) in which the numbers on the mid-line represent the number of scale rows, upper figures refer to the right side of the snake, and figures in parentheses indicate the number of the ventral scale (counted from the anterior end of the series), thus marking the position of the addition or reduction. Addition of a row is shown by a plus sign and the number of the row, whereas reductions are shown by a minus sign and the number of the row that is lost or by a plus sign between the number of two rows that join. According to Dowling, variation in number of dorsal scales characterizes the few genera and species of snakes in which it has been studied. The time and difficulty involved in ascertaining the number of scales explain why it has not been widely used in classification.

Ventral scales on 34 males averaged 134.4 (128 to 139), and on 48 females 133.5 (128 to 137) (Fig. 2.). Barbour (1956:34) found an average of 135.3 ventral scales on 64 males and 44 females, and Gloyd and Conant (_loc. cit._) found an average of 134 for both males and females. The average for the eastern cottonmouth obtained by Gloyd and Conant, however, was 137 ventrals in both sexes. Some of my counts were made before I knew of the standard system of counting ventrals proposed by Dowling (1951a:97-99), in which the first ventral plate is defined as the most anterior one bordered on both sides by the first row of dorsals. Therefore, some inconsistencies may exist in my counts. Where differences occur, Dowling's method probably will indicate the presence of an additional scale, since it appears to begin farther anteriorly on the average, than I began counting.

TABLE 5.--Caudal Scale Combinations in 95 Cottonmouths. U = Undivided; D = Divided.

===================================================================== | Number of scales |------------------------------------------------------------- Number | | | | | | | | | | | | | | | | | of | | | | | | | | | | | | | | | | | samples| D | U | D | U | D | U | D | U | D |U| D|U| D|U|D|U|D -------+---+-----+-----+---+----+---+----+---+-----+-+--+-+--+-+-+-+- 25 | |13-35|10-32| | | | | | | | | | | | | | 11 |1-2|12-33|14-28| | | | | | | | | | | | | | 20 | |16-39| 1-9 |1-3|3-24| | | | | | | | | | | | 20 |1-4| 3-37| 1-21|1-5|1-29| | | | | | | | | | | | 4 | |14-30| 1-8 |1-7|1-8 |1-4|2-10| | | | | | | | | | 3 | 1 |18-23| 1-2 |1-2|6-11|1-3|6-9 | | | | | | | | | | 4 | | 1-17| 1 |1-3|1-8 |1-4|1-3 |1-4|13-22| | | | | | | | 2 |1-2| 4-16| 1 |1-4| 2 | 1 |1-4 | 1 |18-21| | | | | | | | 1 | | 20 | 1 | 1 | 1 | 1 | 6 | 1 | 3 |1|11| | | | | | 1 | | 10 | 2 | 3 | 2 |10 | 1 | 2 | 2 |1| 4|4| | | | | 1 | | 20 | 1 | 1 | 2 | 1 | 1 | 4 | 4 |2| 4|1| 3| | | | 1 | 1 | 13 | 1 | 1 | 1 | 3 | 1 | 1 | 1 |4| 2|4|13| | | | 1 | | 17 | 1 | 1 | 2 | 1 | 1 | 6 | 2 |1| 2|3| 2|7| | | 1 | | 9 | 1 | 1 | 8 | 1 | 3 | 1 | 1 |3| 1|1| 2|1|1|1|6 ---------------------------------------------------------------------

Analysis of caudal scales revealed sexual dimorphism. In the six specimens from Tennessee, Blanchard (1922:16) found the same thing. Caudals averaged 45.4 (41 to 50) on 34 males and 42.6 (39 to 49) on 44 females (Fig. 3). Barbour (_loc. cit._) found an average of 45.7 (30 to 54) caudals in males and 43 (17 to 56) in females. Caudal scale counts by Gloyd and Conant (_loc. cit._) averaged 44 (38 to 49) in males and 42 (37 to 48) in females of _leucostoma_; in _piscivorus_ they averaged 48 (42 to 53) in males and 44 (41 to 49) in females. Another seldom-mentioned, unusual characteristic of the caudal scales of copperheads and cottonmouths is that some are single (usually those at the base of the tail) and others divided (Table 5). To my knowledge, all other species have either single or divided scales the entire length of the tail. See Klauber (1941:73) and Fox (1948:252) concerning correlation of few scales with warm environment.

Dentition

Cottonmouths, like other pit-vipers, have their teeth reduced in number and have enlarged, highly specialized fangs. Small teeth occur on the palatine and the pterygoid in the upper jaw and on the dentary in the lower jaw. The dentary bone bears 17 curved teeth that decrease in size posteriorly. The palatine bears five small, strongly curved teeth, and the pterygoid bears 16 to 18 strongly curved teeth decreasing in size posteriorly. The numbers of teeth mentioned above in each instance refer to the number of sockets rather than the actual number of teeth, because teeth are frequently shed, leaving some of the sockets empty at any one time.

The maxillary bone has two sockets side by side which bear the poison fangs, usually one at a time. During the period shortly before a fang is to be shed, however, its replacement becomes attached in the alternate socket; and both fangs may be functional for a short time. The old fang then becomes weakened at its base, eventually breaks off, and is swallowed. At any one time four or five replacement fangs in various stages of development are found in the gum behind the functional fang. These replacement fangs, which are arranged in alternate rows, gradually enlarge as they move forward in their development and, in juveniles, are generally slightly longer than the fangs that they replace.

In 1963 I examined the fangs of 14 cottonmouths at four- to seven-day intervals for a period of six weeks. The fang-shedding cycle was found to be highly irregular, with a double condition (on one or both sides) occurring one-third of the time. Approximately the same proportion of double fangs was found in preserved individuals. A replacement period of at least five days was observed in one snake. One-half the cycle (from replacement on one side to replacement on the other) varied from five to twenty days, indicating that the cycles for each fang are independent of one another. Bogert (1943:324) found that young rattlesnakes are born with functional fangs in the two inner sockets. Nonsynchronous use of the sockets on opposite sides of the head in rattlesnakes is a later development which results from accidents or other conditions leading to a longer retention of the fang on one side than on the other (Klauber, 1956:723). I found a double set of fangs in cottonmouths only twice in the six-week period. A complete cycle was recorded in ten instances in a period of 19 to 23 days and in two instances in 32 days. One cottonmouth was examined periodically over a 34-day period by Allen and Swindell (1948:12), but a complete fang-shedding cycle was not observed. Fitch (1960:110) reported a 33-day cycle in copperheads; Klauber (1956:726) estimated the normal active life of each fang of an adult rattlesnake to be from six to ten weeks, but he made no observations to confirm his estimation.

Fangs measured from the tip of the notch of the basal lumen to the end of the fang vary from about 1.3 per cent of the snout-vent length in juveniles to about 1.0 per cent in large adults (Table 6). The fangs are longer than those of copperheads (Fitch, 1960:111). Klauber's (1956:736) figures on fang-lengths in all species of rattlesnakes are percentages of total length rather than of the snout-vent length. The fangs of various species of rattlesnakes range from nearly the same proportionate length as those of cottonmouths to some much longer.

From patterns of bites of venomous snakes, Pope and Perkins (1944:333-335) attempted to correlate number, size, and patterns of tooth marks with size and generic identity of the snake responsible for the bite. Distance between fangs is relatively constant for snakes of a particular size (Table 6) regardless of genus, but the fangs of a cottonmouth are directed outward to variable degrees, and puncture wounds could easily resemble those of a much larger snake (Table 7). Also there is no direct relationship between size of snake and toxicity or amount of venom injected. Consequently information of this kind is of little or no value from a medical standpoint.

TABLE 6.--Correlation of Relative Fang-length and Distance Between Fangs at Base with Snout-vent Length of Cottonmouths.

======================================================= |Snout-vent |Number |Average |Number |Average | |length |in |ratio of |in |ratio of | |(millimeters) |sample |fang-length |sample |distance | | | |to | |between | | | |snout-vent | |fangs to | | | |length | |snout-vent | | | |(percent) | |length | | | | | |(percent) | |--------------+-------+------------+-------+-----------| | 200-299 | 3 | 1.33 | 3 | 2.57 | | 300-399 | 7 | 1.30 | 5 | 2.48 | | 400-499 | 13 | 1.21 | 9 | 2.21 | | 500-599 | 12 | 1.22 | 8 | 2.19 | | 600-699 | 7 | 1.17 | 1 | 2.10 | | 700-799 | 5 | 1.07 | 4 | 1.65 | | 800-899 | 1 | 1.00 | 1 | 2.00 | -------------------------------------------------------

TABLE 7.--Contrast in Measurements Between the Base of the Fangs and Between Fang Punctures of Nine Cottonmouths (in millimeters).

================================================== | Distance between | Distance between | Snout-vent | | base of fangs | fang punctures | length | |------------------+------------------+------------| | 7.7 | 13.0 | 400 | | 8.7 | 14.0 | 575 | | 10.0 | 22.5 | 526 | | 11.0 | 18.0-19.0 | 590 | | 12.0 | 18.0 | 793 | | 13.0 | 17.0, 20.0 | 558, 612 | | 15.5 | 23.5 | 800 | | 16.0 | 24.0 | 800 | --------------------------------------------------

HABITAT AND LIMITING FACTORS

Although usually associated with swamps and lowlands along river bottoms, the cottonmouth lives in a variety of habitats ranging from salt marshes to cool, clear streams and from sea level to an altitude of 2300 feet. Shaded, moist areas either in or beside shallow waters are preferred, but cottonmouths occasionally wander as far as a mile from water.

In the pine-oak forests of Nacogdoches County in eastern Texas cottonmouths and copperheads are probably the most abundant species of snakes. Specimens have been collected near Nacogdoches in ponds, swamps, clear and fast-running streams with rock bottoms, and sluggish muddy streams. On the Stephen F. Austin Experimental Forest numerous cottonmouths live in a swamp until around mid-July, when it becomes dry. A small stream west of the swamp seems to be used as a migration route to and from the swamp. Slightly more than a mile downstream cottonmouths are common in a bottomland area. The ground is always moist and no undergrowth occurs; a few small clear springs produce shallow trickles that run into a swamp. Cottonmouths can often be found here, lying in or beside the small trickles.

I have seen cottonmouths in various types of aquatic habitats in Brazoria County. In most places in this area, cottonmouths are found in association with one or more species of water-snakes (including _Natrix cyclopion_, _N. erythrogaster_, _N. rhombifera_, and _N. confluens_), which greatly outnumber the cottonmouth. Interspecific competition may be reduced somewhat by cottonmouths sometimes feeding on water-snakes.

The numerous statements in the literature concerning the habitat of the cottonmouth can be summarized most easily by the following short quotations:

_Agkistrodon piscivorus piscivorus_--"Marshes and lakes; ponds and streams with wooded shores; low country near water; roadside ponds; drainage ditches; coastal 'banks'; keys; some Gulf coast islands; mangrove swamps." (Wright and Wright, 1957:919.)

_Agkistrodon piscivorus leucostoma_--"Cypress, gum, river swamps; alluvial swamps wooded or not wooded; water courses of the south such as rivers, bayous, backwaters of small branches; hill streams in the north; ... marshy places in prairies ... rice fields, bottomland pools; margins of above habitats, pools, shallow lakes, swampy places, temporary flood lands.... In, under, or on fallen timber, in holes in banks, rocky bluffs, crayfish burrows. In short it is very aquatic." (Wright and Wright, _op. cit._:923.)

Geographically cottonmouths differ somewhat in their ecological requirements, but are basically much alike in most respects. The areas of greatest abundance are those having 40 inches or more of annual rainfall. The northern edge of the range has a mean temperature of approximately 38° F. in January in Virginia and 30° F. in Missouri, although the lowest temperature reached in these areas is more important as a limiting factor. The annual rainfall in both Virginia and Missouri amounts to approximately 40 inches. Moisture, as well as temperature, may play an important role in the northward distribution of the species. The eastern cottonmouth seems to be less tolerant of low temperatures than the western subspecies. Mean January temperatures equal to those along the northern limits of the western cottonmouth's distribution are reached in the vicinity of Connecticut, which is north of the geographic range of the eastern subspecies.

The depths to which cottonmouths penetrate into their dens may have a limiting influence upon the geographic range, especially in the northern extremes. Bailey (1948:215) discussed the possibility that populations of snakes may be significantly depressed because of winter kill of individuals that "hibernate" at shallow depths. He speculated also that the short growing season does not allow enough time for the essentials of existence to be carried out, and the prolonged period of inactivity overtaxes the energy reserve of the species.

Available food does not seem to be of much importance as a limiting factor, for the cottonmouth is remarkably indiscriminate in its choice of prey, feeding upon almost any vertebrate animal that happens to come within reach. Competition for food, however, may play an important role.

REPRODUCTION

Courtship and Mating

A review of available literature indicates no records of courtship of the cottonmouth other than statements that breeding occurs in early spring. In a close relative, the copperhead (see Fitch, 1960:159-160), mating occurs almost any time in the season of activity but is mainly concentrated in the few weeks after spring emergence, at about the time when females are ovulating. Klauber (1956:692) concluded that along the southern border of the United States rattlesnakes normally mate in spring soon after coming out of their winter retreats; but farther north where broods are produced biennially, the mating times may be more widely dispersed, and summer and fall matings may even predominate.

The only record of copulation in the cottonmouth was reported by Allen and Swindell (1948:11), who observed a pair copulating for three hours on October 19, 1946, at the Ross Allen Reptile Institute. Davis (1936:267-268) stated that courtship in cottonmouths is violent and prolonged but did not note any nervous, jerky motions or nudging of the female along her back and sides as had been observed in other genera of snakes. Carr (1936:90) saw a male cottonmouth seize a female in his mouth and hold her, but no courtship followed.

Reproductive Cycles

Many persons have assumed that gestation periods in snakes are the intervals between mating and parturition, and that mating and ovulation occur at approximately the same time. However, retention of spermatozoa and delayed fertilization indicate that copulation is not a stimulus for ovulation.