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Boa constrictors tend to be very easy-going
snakes. Disposition varies among
individuals, between races (imperator's have a nasty reputation), with
age, and in response to handling. If a
boa constrictor is in a bad mood, the head and neck usually are thrown back in
an S-curve and the animal may hiss long and very loudly. It is not hard to tell when a boa
constrictor wishes to be left alone.
After biting, the snake may let go immediately or clamp down with its
jaws and coil tightly around anything available, including arms and legs. Holding the animal's head under a running
tap may convince it to release its hold.
Otherwise, a flat card or blade must be forced between one of the jaws
and whatever it is biting. At this
point, the other jaw can be unhooked.
Boa constrictors seem to become more familiar
with people as a result of handling and so are less likely to bite if taken out
of their cages every now and then. All
of the young which I have raised can be handled freely. My boa constrictors have bitten me in two
situations. One is during or just after
feeding, and the second is during their "adolescence." Tongs for holding the food item help greatly
in avoiding mistakes on the snake's part during feeding. Handling the snake after feeding is not
recommended, since it is prone to bite and also may regurgitate. Putting your hand in front of a boa
constrictor after you have been holding food is asking for trouble. Boa constrictors feed very reliably and
initially seize prey on the basis of smell rather than vision. Thereafter, their sense of smell seems to be
swamped and they may bite anything that moves suddenly in their vicinity. Further details on feeding are given below.
I have noticed
that one to one and a half meter (three to five feet) boa constrictors
sometimes become nervous when handled.
They also may bite lightly if touched suddenly on the body. These bites may startle you, but are not
serious and do not hurt much at all (though you will bleed a bit). They can be avoided by handling the snake in
a gentle manner without any sudden moves on your part. In general, boa constrictors should be
supported fully and allowed to wrap around your hands and arms. They fear situations where they might
fall. Holding an animal around the body
at an arm's length definitely tends to make it feel insecure. In any event, this proclivity to biting
seems to be part of an "adolescent" stage that the snake will grow
out of. Bites of boa constrictors less
than one and a half meters (five feet) generally have the severity of a cat
scratch, but those from larger boas can require a few stitches if the skin
tears when the person or snake pull back.
If you feel apprehensive about the size and/or temperament of your
snake, you should sell it and get a smaller and/or nicer one.
Housing (Vivarium Research Group, Inc. 1998)
Cages or aquaria made with wood, plastic,
fiberglass, glass, etc. serve well for boa constrictors. No screen should be used for the top or
anywhere else in the cage. Using
screen in the cage is a common mistake.
Some individuals will rub their noses on screen or other rough surfaces
until they develop abrasions and infections (see mouth rot under Health), will
not feed, and starve to death. Even if
the snake recovers, the disfigurement will be permanent since the scales will
not grow back. Sometimes the abrasions
can even cause fatty tumors
to develop. Snakes can be remarkably
quick in rubbing their snouts raw, say several hours. I recommend pegboard for tops as it is readily available, cheap,
and easy to work with. Since snakes
require very little air circulation, cages can be closed off to make them
easier to heat (which is a great deal more important for tropical snakes like
boa constrictors). Cages should be
large enough for the snake to stretch out in, if possible. Large animals should be kept in cages with a
long dimension at least two thirds of the snake's length. Though boa constrictors like to climb, floor
area is more important than height in a cage, particularly for large individuals.
Much controversy exists over what to put in
the cage besides the snake. The
following is my personal preference. In
general, I like to keep the interior of the cage as simple as possible, since
it facilitates cleaning, changing water, and taking the snake out of the
cage. Naturalistic tropical vivaria can
be used for small boa constrictors (Vivarium Research Group, Inc. 1998). Careful consideration should be given to
rocks, branches, and such that are placed in the cage as the inhabitant's
safety depends upon it. Boa
constrictors are not bright nor are they adapted to living in cages. As a consequence, they potentially can get
caught in rock holes or branch forks that can cause injury or death. Movement through tight spots also can scar
the boa when done during the shedding period.
Many people use newspaper, cedar shavings,
Astro-Turf, dirt, sand, etc. in the bottom of the cage: I recommend pine shavings. Some boa constrictors, particularly small
ones, like to burrow, and pine shavings are the only substrate other than cedar
shavings that allow them to do this. A
depth double the diameter of the snake suffices for burrowing. Aside from being more expensive than pine
shavings, cedar shavings are too aromatic and some people assert that they are
detrimental to the health of snakes.
Pine shavings are absorbent and dry out quickly. A damp cage leads to scale mite population
explosions and blister disease (see under Health, Wright
1995). Feces and surrounding shavings
can be easily removed and replaced with fresh bedding. Spot cleaning should be carried out at least
once a week. All bedding should be
replaced and the cage cleaned thoroughly at least twice annually. The one disadvantage of shavings is that
snakes can accidentally ingest them while feeding; see Food and Water
for further discussion of this problem.
Many ranch and feed stores carry bale-size packages of pine shavings for
around ten dollars.
Placing a layer of plastic sheeting in the
bottom of a wooden cage will prevent water and other fluids from wetting the
lumber and causing irremovable odors.
The plastic must be firmly attached to the cage with no holes or free
edges; otherwise, a boa constrictor may be depended upon to get under it. Boric acid power can be sprinkled beneath
the plastic to control mites, ants, and other arthropod pests.
Since boa constrictors are tropical
poikilotherms, their cages must be heated.
Otherwise, they develop colds and pneumonia, have trouble with digesting
food, may regurgitate after eating, and become more susceptible to many
diseases and pests, in particular amoebiasis, blister disease, and scale mite
infestations (see under Health).
Individuals will form aggregations in captivity, evidently in order to
retain heat (Myres and Eells 1968).
Particularly while digesting food, boas attempt to maintain a
temperature from 31 to 32°C (88 to 90°F) (Regal 1966, Myres and Eells
1968). Wild caught boa constrictors
should be maintained above 27°C (81°F), but my captive-born animals do well at
temperatures as low as 24°C (75°F).
Some kind of localized heat source should also be present, so the snake
can achieve a temperature appropriate for digestion. If the room cannot be maintained at a temperature higher than
24°C (75°F), supplemental heat must be provided for the cage. Hot rocks are made of plaster with an
embedded electric heating element and work well in a small cage if they can be
obtained. Heating pads that are placed
in the bottom of the cage can get wet and sometimes do not provide sufficient
heat. Subfloor heating with light
bulbs, heater tape or ribbon, or heating pads may work in some situations. An incandescent light or space heater near
the cage are also viable solutions.
Incandescent lights and other filament heaters can be wired to a
transformer or light dimmer to control their heat output (Logan 1972). Care must be taken to avoid cracking glass
or overheating the cage with the heat source.
An aquarium heater or incandescent reflector may be used inside the
cage, but it should be suitably isolated so the boa cannot touch it and burn
itself. Light reflectors used within a
cage should be set up so that no hot areas, wires, or sharp edges are
exposed. Whatever heating option is selected,
the temperature should be checked every few days to confirm that an appropriate
temperature range is being maintained.
Boa constrictors quickly develop colds and their susceptibility to other
diseases also increases at low temperatures.
Boa
constrictors also require high relative humidity, preferably around 70 to
80%. This can be a real problem in the
winter when heating the cage drops the humidity. Boas often have problems with shedding and may develop blister
disease if the humidity is too low (see under Health). The most direct way to raise the humidity is
to spray the boa and its cage every day or two. Care must be taken so the cage does not become excessively damp,
as this condition will encourage scale mite infestations and blister
disease. The presence of plants in the
cage or use of a humidifier may also help.
One advantage of a boa constrictor as a pet
is that it can go without food and water for weeks, thus freeing its owner for
fairly extended trips. The concomitant
disadvantage is that snakes will not beg for food as a cat or dog will, so many
owners neglect the snake's feeding. In
combination with their elongated morphology and the difficulty of recognizing
that the animal is indeed becoming thin, this results in many captive snakes
getting so weak that they can no longer feed.
For these and other reasons, starvation is probably the most common
cause of death in captive snakes (see under Health).
Water should be present in the cage at least
a few days out of the week. Boas like
very much to soak in water on occasion, so the container should be large enough
to hold snake and water without overflow.
I keep water containers a third to half full. Large boas will tip over containers, unless they are heavy or are
fastened in place. Water should be
changed once or twice a week or whenever feces are deposited in it.
Considerable latitude exists in food item
size, amount of food per feeding, and frequency of feeding for snakes. Table 3 provides a rough guide for boa
constrictors of different sizes.
Overall amount of food eaten can vary easily from one half to twice as
much as indicated in the table. Amount
of food given will depend upon temperature and how high a growth rate is
desired. Boa constrictors typically eat
much less in winter than in summer.
Length
of Boa
|
Size and
Type of Food Item |
Frequency
of Feeding |
|
40-60 cm
(16-24 in) |
baby to
3-week-old rats, mice |
1 mouse per
week |
|
0.6-1 m
(2-3.3 ft) |
3-week-old
rats, mice |
2-4 mice per
week |
|
1-1.5 m
(3.3-4.9 ft) |
half-grown
rats, chicks |
2 rats per
week |
|
1.5-2 m
(4.9-6.6 ft) |
rats,
1-month-old chickens |
2 rats per
week |
|
2-2.5 m
(6.6-8.2 ft) |
rats,
half-grown chickens |
3-4 rats
every two weeks |
|
2.5 m (8.2
ft) or more |
rats,
chickens, rabbits |
1 rabbit
every 3 weeks |
Since boa constrictors feed very readily, some precautions are
necessary, particularly if more than one animal are present. It is best to separate individuals to
different containers, since they will attempt to seize anything that moves
nearby when they are feeding and will also try to bite and constrict food that
another snake already has. Heavy
leather or rubber gloves that extend to the elbows are useful for handling
large boa constrictors during feeding sessions. Boa constrictors feed so readily (and sloppily) that they
sometimes engulf shavings, gravel, or other indigestible materials as well as
the food. The snake may not be able to
pass or regurgitate the foreign matter if it is large enough relative to the
animal's size. These items can cause
stomach ulcers that will kill the snake.
The only sure way to avoid this problem is to feed the boa constrictor
in a container having only the snake and food present. Any aquarium or plastic box will serve for
small boa constrictors, but styrofoam boxes are the cheapest and most
handleable alternative for large individuals.
I recommend that only animals that already
have been killed be given to boa constrictors.
The most important reason for this is to prevent injury to the snake as
a result of bites or scratches from the prey (Klingenberg 1998). Fry (1973), a veterinarian with extensive
experience in reptile treatment, states that the most common traumatic lesions
he deals with in snakes are rat bites in boa constrictors. Deaths rarely result from these bites, but
permanent scars do since destruction of underlying soft tissues usually
occurs. Killing the food animal
beforehand is also more humane for the prey.
Boa constrictors do not care whether the animal they are eating is alive
or dead; they usually constrict it as if it were alive. Food items can be offered to a boa
constrictor with tongs, by dropping the food into the snake's container, or by
leaving the food in its cage. Shavings
should be swept clear of the area in the cage where feeding takes place.
If a boa constrictor refuses to eat, it is
either too cold, already full, frightened, shedding, sick, or pregnant. Full, shedding, and pregnant boa
constrictors should not be fed, cold boas should be kept warmer, frightened
individuals may have to be left with their food overnight, and sick animals may
require treatment or force-feeding (see under Health). Live food should never be left with a
snake, unless the situation is kept under observation. Rats and mice can and will chew patches of
skin off of a snake (Klingenberg 1998).
Newborn boas have a substantial amount of yolk in the gut and spend
their initial one to two weeks shedding.
They should never be fed until after their natal shed, as doing
so increases the risk of amoebiasis or other intestinal infections (see under Health).
Since boa constrictors readily will accept dead
animals, it is often convenient to obtain a large amount of food, kill and
freeze it, and defrost suitable portions at the time of future feeding
sessions. The food only needs to be at
room temperature. The method of choice
for euthanasia is carbon dioxide asphyxiation with cervical dislocation as an
alternative. Freezing destroys
parasites which might be passed on to the snake, but it may also be deleterious
for vitamins. I doubt that this is
true, since I have fed frozen animals to captive born boa constrictors for
years, and the snakes exhibit normal growth and no overt vitamin
deficiencies. For whatever reason, if a
snake should refuse to eat, the food should always be discarded and never
refrozen. The convenience of frozen
food is another strong reason for giving boa constrictors dead animals to eat.
Snake
food may be obtained from a variety of places.
Pet shops carry rats and mice.
Ranch and feed stores often stock chicks, chickens, and rabbits. These animals also are advertised in the
classified section of newspapers, though they may be intended as pets. I do not recommend succumbing to the
temptation of obtaining animals such as puppies or rabbits that are being
advertised only as pets. Laboratories
sometimes get rid of large numbers of research animals and do not mind if they
are used to feed snakes. Experimental
animals from laboratories should be free of toxic substances and should not
have been killed with ether, phencyclidine (Sernalyn), sodium pentobarbital
(Nembutal), or other barbiturates.
Using animals with questionable origins or edibility is not worth the
risk. Wild animals should be avoided as
a source of food. The need for snake
food will not justify the expense and effort required to maintain a rodent
colony, rabbit hutch, or chicken coop.
However, if excess animals are available from one of these sources, they
can be fed directly to a snake or frozen for later use.
Like most animals, boa
constrictors have a cubic length-weight relationship. Figure 2 is based on 360 observed weights for snakes of different
lengths in English units. Note that the
length and weight axes have logarithmic scales with linear numeric labels. The equations were derived from data on 81
newborn and 15 older boas that ranged from 1.3 to 8.3 feet (0.41 to 2.53
meters) in length and from 0.062 to 30.5 pounds (0.028 to 13.84 kilograms) in
weight. Multiple measurements were
taken on specimens that had grown substantially. Boas were measured and weighed just prior to being fed. Intermediate values can be determined by
working through one of the equations with any calculator having logarithm and
exponentiation functions. The natural
logarithm formulae can be converted to base ten logarithm versions by dividing
the intercepts (‑0.5065 or ‑3.537) by 2.3. Alternatively, the graph itself can be used
to obtain a direct estimate of weight for a particular length.
Since length "explains" 99 percent
of the variation in weight, the relationship of length and weight is very
tight. The standard deviation of weight
about the regression line amounts to about fifteen percent of the weight
predicted for a particular length, so the predicted weight plus or minus
fifteen percent is an appropriate range to maintain an animal's weight
within. If a boa constrictor weighs
less than two standard deviations (thirty percent) below the weight calculated
for its length, more feeding is required.
Conversely, if the snake is thirty percent or more heavier than its
predicted weight, it is too obese. It
should be noted that the weight data for the above regression relationship were
obtained for snakes just before feeding. A boa constrictor easily can eat without harm up to a quarter of
its body weight during a feeding session.
Growth rates
over time are a great deal messier than the length-weight relationship, since
growth is affected strongly by temperature, amount of food, sex of the boa
constrictor, and probably the snake's area of origin. Figures 3 and 4 show age isoclines based on seven females and
four males whose age is either known or can be estimated closely. The graphs show that the highest growth
rates occur in the first three or four years of life. After this, males appear to approach a maximum of about 75 inches
(191 centimeters) and eleven pounds (five kilograms). Females continue to grow to much larger sizes, and their data
points indicate that a maximum has not been reached by sixteen years of
age. The data include a ten-year-old imperator
female that measures around six feet (two meters), weighs about nine pounds
(four kilograms), and comes from Mexico, an area where individuals may attain a
smaller maximum size than do the constrictor's of South America.
Only a spotty
and somewhat puzzling literature on reproduction in boa constrictors currently
exists. This is particularly
surprising, since the species is an abundant, widely occurring snake that is
often bred in captivity. Males may be
distinguished from females by their greater development of the "spurs,"
proportionately longer and fatter tails, and higher numbers of caudal plates
(Table 4, Figures 5 and 6). Data on the
true sex were obtained by dissection, spur development, or breeding. "N" indicates neonates and
"N*" denotes constrictor-imperator intergrade neonates
in the Figures. Newborns can be sexed
by a technique used for small boids.
The technique involves catching the base of the tail between the thumb
tip and index finger, applying light pressure, and pulling the tail through the
opening. In males, blood seems to get
caught in the hemipenes within the tail and the heads of the hemipenes can be
palpated as they pass beneath the thumb tip.
Eversion of the hemipenes or probing is unnecessary in sexing boa
constrictors. Both approaches also seem
to be inaccurate and potentially dangerous to the animal.
Table
4. Sexual Dimorphism in Boa
Constrictors.
4.1. Literature Records of Caudal
Plate Numbers in Males and Females.
|
Subspecies |
Males |
Females |
References |
|
constrictor |
52 - 58 |
43 - 59 |
15,27 |
|
imperator |
55 - 70 |
48 - 61 |
61,63,64 |
4.2. Caudal Plate Numbers of Males and Females
in the Colony.
|
Sex |
N |
Mean |
Std. Dev. |
Range |
95%
Confidence Interval |
|
Male |
13 |
57.85 |
2.91 |
54 – 64 |
56.26 -
59.43 |
|
Female |
17 |
50.76 |
1.68 |
47 – 53 |
49.97 -
51.56 |
4.3. Tail Length as a Percentage of Total
Length for Males and Females in the Colony.
|
Sex |
N |
Mean |
Std. Dev. |
Range |
95%
Confidence Interval |
|
Male |
17 |
11.55% |
0.99% |
9.76 -
13.68% |
11.08 -
12.02% |
|
Female |
20 |
9.85% |
0.63% |
8.70 -
10.64% |
9.58 -
10.13% |
|
|
Males do not show aggression
toward one another, though they do have typical boid courtship behavior
involving topping and titillation of the females with their spurs. I keep pairs together throughout the year
and have never used male combat as a stimulus for mating. Colony males have never needed any
encouragement to court. Individuals in
my colony reproduce under the natural diurnal cycle observed at about 30°
Latitude N. I have never purposely
cooled my boa constrictors in the Fall, though their ambient temperature does
drop from the 28-34°C (82-93°F) range to 25-29°C (77 to 84°F). My animals breed annually from August to
March with a peak in January, nearly the same as the December to March mating
period observed in Trinidad (Mole and Ulrich 1894, Mole, 1924).
My impression is that females require relatively high body weight to assure ovulation. Reproductive females accumulate huge abdominal fat bodies in the latter third of their bodies that can increase their normal body weight 25 to 30%. Owners often mistake this fat accumulation for pregnancy and then assume the eggs are "reabsorbed" when no birth occurs. Egg resorption is known only in certain mammals such as people. Resorption can only take place in animals with small eggs, not in those groups with large yolks like reptiles and birds. In boa constrictors, the presumed resorption only involves the slow utilization of the accumulated fat bodies when ovulation fails to occur. Soon before or after a female mates, I have noticed a large localized swelling three-fifths of the way down the body that lasts several days and marks the time immediately before ovulation (photo below). Since this happens only during a restricted time when the female is receptive, it probably results from yolking and/or aggregation of the eggs prior to ovulation. This phenomenon also has been noted in various other pythons, boas, and even some colubrids (Van Mierop and Bessett 1981, Barker and Barker 1995). It probably provides the best indicator of the start of gestation. Egg yolking evidently occurs very quickly in birds and reptiles (chickens do it in nine days). Up to sixty 2 to 3 inch eggs may by yolked in the boa constrictor's ovaries during this short period. The large fat bodies serve as the source for yolk production.
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Five females in my collection have given
birth from 119 to 133 days after swelling of the midbody was observed (Figure
7). Actual mating serves as a poor
indicator of the beginning of pregnancy, since ovulation may not happen
simultaneously with mating or at all.
Boa constrictors generally have their young four and a half to six
months after copulation, as has been reported from a commercial culture
operation in Colombia (Otero de la Espriella 1978) and for constrictor
and imperator females that have mated in captivity in Switzerland
(Gensch 1969, Meyer-Holzapfel 1969).
Mated females probably store sperm in the two uterine horns. Females eat little or nothing during the last
half of pregnancy. Pregnant females may
remain tightly coiled and thermoregulate at 27 to 32°C (80 to 90°F) (photo
below). Pregnant boa constrictors
should be maintained at 28 to 34°C (82 to 93°F). Extreme temperatures for even a short time during pregnancy can
cause deformities, primarily in the caudal region. Stillbirths and unfertilized or partially developed ova are not
uncommon, especially in initial, low temperature, or disturbed pregnancies.
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40 baby B.c.
constrictor. What you finally get
5 months after ovulation. |
Litters have been obtained during August in
Belíze (Neill 1962), from November to February in Peru (Dixon and Soini 1986),
and in June and July from imperator and constrictor females that
mated in captivity in Switzerland (Gensch 1969, Meyer-Holzapfel 1969). Females in my colony have given birth from
February to August with a tendency toward May and June (Figures 7 and 8). This only leaves September and October. The reproductive cycle may vary both
geographically and in response to conditions of captivity. Live births in my colony have numbered from
four (in a constrictor-imperator cross) to forty-nine with a mean
of 31.3 per litter in fifteen pregnancies.
Litters from pregnancies with no complications have yielded from sixteen
live births and one infertile egg to forty-nine live births and six stillbirths
or infertile eggs. All of the litters
in my colony have included at least a few eggs resulting from unfertilized ova
or embryos that die during development.
Examination of these eggs has always revealed solid yolk or dead embryos
or fetuses. One set of identical twins
has been identified in approximately 600 births. This pair had a common yolk sac and extremely high pattern
concordance. Live births have comprised
60% (469 out of 776) of the total production of eggs in this colony (Figure 8).
Many problems can
accompany pregnancy. Four unsuccessful
pregnancies, due either to genetic incompatibility or premature termination,
and one in which twenty-eight unfertilized eggs were produced, have also
occurred in my colony. Low temperature
and other adverse prenatal conditions contribute to congenital defects that
include eye hydrocele, scoliosis, prolapsed hemipenes, cleft palate, incomplete
umbilical closure, and spina bifida.
Newborns normally measure 46 to 56 cm (18 to 22 in.) in length, but may
be considerably smaller if the six inch umbilicus twists and prevents transfer
of yolk to the developing boa constrictor.
Structural twisting of an oviduct can prevent the passage of young and
eggs from both horns anterior to the block.
Retained eggs and young encyst, but can be removed
surgically. Feeding a large
meal to a pregnant female can cause her to abort. An obviously pregnant female should be fed lightly or not at all.