The Evolution and Life History
of the
Florida Cottonmouth
By:
Emily Hess
4-10-08
PCB 4674
Professor Ann McNicol
The Florida Cottonmouth, also known as Agkistrodon piscivorus conanti,
is one of many of Florida’s snakes. It was named in honor of the deceased
herpetologist, Roger Conant. The large, venomous Florida Cottonmouth exhibits
an interesting evolutionary life history consisting of their habitat, prey,
reproduction, abundance, behavior and external features.
Evolutionary History & Adaptations
The Florida Cottonmouth descends from the Genus Agkistrodon, which
descends from the suborder, Squamata. The Florida Cottonmouth descends
from a family of entirely aquatic snakes that have lost their broad belly-scales.
The Florida Cottonmouth has approximately 47 relatives in the Agkistrodon
Genus. Snakes originated during the Cretaceous period from monitor-like lizards.
Some say that the lack of legs was as adaptation to subterranean life (indeed,
even today's most primitive snakes are subterranean), others that this appeared
as the first snakes roamed grassy environments, using lateral undulation
movements as an easier way of locomotion in these habitats (Anitei, 2006).
Snakes had an ‘evolutionary boom’ because of the increase in rodents, which is
a primary prey for snakes. Snakes later developed a chemical weapon to kill their
prey with minimal injury risk. “Their venom evolved initially in salivary glands and
in many species, the venom still has a digestive role, fact proved by the necrosis
of the tissues at the bite site” (Anitei, 2006). The snake’s venom eventually
became their main source of defense, mainly to warn intruders. There are
currently approximately 2000 snake species, with about 400 of them possessing
venom that is strong enough to have an effect on humans.
Closely-Related Species
When the Genus Agkistrodon originated, it was believed to occupy
temperate habitats, with ancestral subsequent tropical evolution. They were
believed to evolve from the Mexican cantils. It is believed that the Genus
Agkistrodon, subdivided from the West coasts of Mexico, into subspecies A.
bilineatus, A. piscivorus, and A. contortrix. The Florida Cottonmouth originated
from the subspecies A. piscivorus. This genus used to be much larger and
included: the Malayan pit viper found in Southeast Asia, moccasins found in Asia,
and humped-nose vipers found in India and Sri Lanka.
Some close relatives of the Florida cottonmouth include the Water Snakes
of the genus Nerodia, copperheads and the Mexican cantils. The Florida water
snakes are often mistaken for the Florida cottonmouth.
External Features
Coloration/Scale Form
The Florida Cottonmouth is dark gray-brown, with broad, paler bands. This
is a form of camouflage for the water-deposited sediment and algae. Florida
Cottonmouths that live in cleaner waters have more noticeable patterns and
lighter brown lower sides. When Florida Cottonmouths get very old, they turn
almost entirely gray or black. “There are 25 rows of keeled dorsal scales at
mid-body and the scales beneath the tail occur in a patter by which Agkistrodon
can be identified even from their shed skins, because for 2/3 of the tail’s length
the sub caudal scales occur in a single row” (Tennant, 1997, p. 215).
Venomous Fangs
There are very few people bitten by Florida Cottonmouths. The mortality
rate in the U.S is less than one person a year. “Envenomation by Agkistrodon
picadors can be serious in terms of tissue death, however, for while its toxins are
less lethal than those of most rattlesnakes” (Tennant & Bartlett, 2000, p. 491).
The jaws of cottonmouths are very wide with their fangs ranging up to .75-inches
long. The largest amount of venom yielded by a Florida cottonmouth was over
1,000 milligrams.
Size/Weight
The Florida cottonmouth is the largest of the three cottonmouth races. The
largest Florida cottonmouth recorded was measured at 74.5 inches. “The
proportionately massive trunk of large cottonmouths would have made that
animal enormous, but most A. p. conanti are much smaller; the majority of adults
attain no more than 38 inches” (Tennant & Bartlett, 2000, p. 492). Male Florida
cottonmouths are longer and can be twice as heavy as females.
Habitat
(A Florida cottonmouth in its natural
habitat)
The Florida cottonmouth is found almost everywhere in Florida, except for
cities. Florida cottonmouths can do well in dry environments and can often be
found in dry forests or grassland areas. However, the Florida cottonmouth is
more abundant in aquatic environments. Migration is subjected only to its
home-range. The Florida cottonmouth has acquired its own niche for and aquatic
environment.
The Florida cottonmouth is mostly associated with water. It also belongs in
the only subspecies of the Agkistrodon genus to have taken an aquatic habitat
and existence. “Although cottonmouths generally live within a half-mile of
permanent fresh, brackish, or salt water, dry forest and grassland are sometimes
occupied, while in spring, flooded prairies are prime foraging sites” (Tennant,
1997, p. 214). The Florida cottonmouth can also be expected to be seen on
streams and riversides, salt marshes, resting or fallen tree trunks in woodland
ponds.
Abundance
The Florida cottonmouth is a K-selected species. It is a larger organism,
with a longer life expectancy, and it reproduces many times over its life. The
Florida cottonmouth is in high abundance in salt marshes and low-lying saline
barrier islands that border Florida’s peninsula. The only place in Florida where
the Florida cottonmouth is not in high abundance is in the lower Keys. The
Florida cottonmouth can also be found in the extreme southeastern and
southwestern Georgia, and in southern Alabama. The abundance of the Florida
cottonmouth has diminished since Florida’s growing population. “The Florida
cottonmouth is still common in undeveloped areas, and where thick vegetation
stifle the humid air above small, leutic bodies of water its unique musky scent is
sometimes noticeable” (Tennant & Bartlett, 2000, p. 492).
Prey
The Florida cottonmouth is, as all snakes, a carnivore and predator. It is
an intraspecific and interspecific competitor. The Florida cottonmouth has very
interesting feeding habits. Frogs are perhaps their most common form of prey,
but they are not limited to feeding on fish, hatchling alligators, cottontails, swamp
rabbits, water birds, sizable water snakes and even smaller cottonmouths. The
Florida cottonmouth will also try and eat dead prey that are too fast or large to
eat normally. “Many cottonmouths are killed by vehicles as the snakes try to eat
already dead animals from busy roadways” (Bartlett & Bartlett, 2003, p. 160). The
Florida cottonmouth is also nocturnal, and prefers to hunt at night. “If in the water
when prey is identified, cottonmouths quickly swim to it, seize it, and hold it in
their mouths. On land, they either ambush prey or actively pursue it” (Ernst,
1992, p. 70).
Predators
The Florida cottonmouth has few enemies. Their only true threats are
alligators and humans. “Since the alligator has been protected, there has been a
noticeable decrease in cottonmouth populations at certain areas of Florida”
(Ernst, 1992, p. 71). Young Florida cottonmouths are prey to a number of
animals including: large fish, bullheads, large-mouth bass, snapping turtles,
different birds, and even larger cottonmouths.
Reproductive patterns
(a young cottonmouth)
The age where Florida cottonmouths reach sexual maturity is around 18
months. The Florida cottonmouth does not lay eggs, as most reptiles, they are
ovoviviparous. The Florida cottonmouth also exhibits an iteroparous method of
reproduction. The young are developed inside their mothers in a shell-less egg.
The adult males initiate contact by following pheronomes released by the female
during the spring and fall. “Courtship involves dorsal tongue-flicking by the male,
as well as rubbing his chin on the female’s back before attempting copulation”
(Tennant, 1997, p. 215). The female can store viable sperm for long periods. The
normal clutch size for the Florida cottonmouth is approximately 3 to 12 babies
from August to September. There has been hybridization occur among the
Southern copperhead, Agkistrodon contortrix contortrix, and the Florida
cottonmouth.
(Hybrid of Southern copperhead and
Florida cottonmouth). The evolutionary trade-off for the Florida cottonmouth is in
its reproduction. “The newborns are so stoutly proportioned that gravid
cottonmouths average only 5 to 6 offspring per litter” (Tennant, 1997, p. 215).
Behavior
The Florida cottonmouth is quite bold in its actions. They do not ‘nest’
together, since the larger ones would soon eat the smaller ones. “Although some
cottonmouths show little fear of humans, none attack-alone or en masse-and
even their chracteristic open-mouthed gape is actually a rather passive defensive
gesture because, unless the mouth itself is touched, wide-jawed cottonmouths
often fail to strike even when prodded elsewhere on their bodies” (Tennant, 1997,
p. 216). Florida cottonmouths can also bite underwater. This is how they catch
fish. The Florida cottonmouth usually always has its head tilted upward. In
Southern Florida, they are active in every month, but are less active in January to
April. “The Florida cottonmouth is more tolerant of cold than most snakes, and is
one of the last to enter hibernation” (Ernst, 1992, p. 66). Therefore, the Florida
cottonmouth is an ectotherm, but is also a homeotherm. The maximum life span
recorded for a Florida cottonmouth was 21 years.
Symbiotic Associations
Seahorse Key is a remote island in Florida that the Florida cottonmouth
occupies in abundance. “Scientists have long puzzled over how many snakes
can thrive on an island with no fresh water and only a scant number of mammals
to prey upon” (National Geographic). It is believed that a symbiotic association
with the other major inhabitants of the island, seabirds. The snakes are not
preying on the birds, but live on the many fish that the birds drop, vomit and
excrete.
References
Anitei, Stefan. "The Evolution of the Snake Venom Injecting Apparatus - How
dangerous are snakes?" Softpedia. 25 Nov. 2006. 10 Apr. 2008
<http://news.softpedia.com/news/The-Evolution-of-the-Snake-Venom-Injecting-A
pparatus-41054.shtml
Bartlett, R.D., and Patricia Bartlett. Florida's Snakes: A guide to their
identification and habits. Gainesville, FL.: University Press of Florida,
2003
Ernst, Carl H. Venomous reptiles of North America. N.p.: Smithsonian
Institution, 1992
"Florida: A True Symbiotic Relationship Between Snake-Birds." National
Geographic. 20 Apr. 2007. 15 Apr. 2008 <http://www.thebubbler.com/
forums/break-room/
10963-florida-true-symbiotic-relationship-between-snake-birds.html>.
Tennant, Alan. A Field Guide to Snakes of Florida. Houston Texas: Gulf
Publishing Company, 1997
Tennant, Alan, and R.D Bartlett. Snakes of North America: Eastern and Central
Regions. Houston Texas: Gulf Publishing Company, 2000.