Probably the best known among all carnivorous
plants because of its swift movement of trap leaves, the Venus flytrap (Dionaea
muscipula) grows in the coastal savannas of North and South Carolina in the
This is the only region in the world where the plants can be seen
in their native habitat. The plants are typically found on a moist surface in
the open pine tree forest, sometimes on a thick mat of sphagnum moss, sometimes
right on the white sand surface, often in company of other carnivorous
plants in the area such as sundews and terrestrial bladderworts.
The plants are federally protected ..????..
The genus name Dionaea is from
Dione, the goddess of
love, in Greek mythology. Venus, in Roman religion, is identified with the
Greek goddess, Aphrodite, whose mother, according to one account, is
The genus Dionaea is monotypic; that
is, there is only one species, Dionaea muscipula. The genus belongs to the sundew family
In a historical letter dated Jan. 24, 1760,
Arthur Dobbs, then Governor of North Carolina, wrote, " ...But the great wonder
of the vegetable kingdom is a very curious unknown species of sensitive; it is a
dwarf plant; the leaves are like a narrow segment of a sphere, consisting of two
parts, like the cap of a spring purse, the concave part outward, each of which
falls back with indented edges (like an iron spring fox trap); upon anything
touching the leaves, or falling between them, they instantly close like a spring
trap, and confine any insect or anything that falls between them; it bears a
white flower; to this surprising plant I have given the name of Fly Trap
The Venus flytrap uses a snap trap (sometimes
referred to as steel trap), the most advanced trap mechanism to be found
among carnivorous plants.
The plant forms a rosette of leaves emerging from a
short white rhizome (underground stem) with fibrous roots. The leaves, which
can grow up to 10cm, are of two parts: a flat petiole (leaf stem) and a leaf
blade modified into a trap.
The trap portion consists of two semicircular
lobes united along the midrib of the leaf blade. Around the margin of each lobe
grow stiff, spine-like guard hairs (15 to 20 along each margin), which mesh
together when the trap closes to prevent the prey's escape. Along the inner edge
of each lobe just below these marginal spines runs a narrow band of nectar
glands which secrete sugary substance to attract potential
prey. Much of the inner lobe
below is crowded with numerous digestive glands, which often give the trap
surface a bright-red coloration. Each inner lobe
surface has three -- sometimes 4
or more -- fine bristles located in a triangular pattern. These are trigger
hairs, which are sensitive to physical stimulation and, when properly
stimulated, initiate a rapid trap closure.
When an unwary insect brushes these hairs,
the trap snaps shut, usually in less than half a second. The guard hairs of each
lobe mesh together to prevent the insect's escape, and the prey is hopelessly
confined between the two lobes. The insect's effort to free itself further
irritates the trigger hairs, causing the lobes to close more tightly. This
pressure sometimes crushes a soft-bodied insect. In several
hours, as the lobes are tightly
sealed, the trap becomes filled with digestive fluids secreted from the
glands on the lobe surface, and the captured
prey begins to dissolve. The trap remains
closed during the digestive process which lasts for a week to ten days depending
on the size of the prey. After the nutrients of the insect body are absorbed by
the plant, the trap opens slowly. Inside the now dry trap is the remains of the
hard shell part of the consumed insect. Wind and rain clean the lobes and
the trap is ready again for another meal. A single trap is usually capable of
repeating this process only three times or so during the life of the trap. After
that it becomes insensitive to stimulation and dies, but new trap leaves are
continuously sprouting out from the rosette center during the growing
season of spring through summer.
When a trigger hair is stimulated by a piece of wood, or a finger, the trap also
snaps shut. In this case, however, the trap opens the next day, since the plant
does not find any nutritious object inside the trap.
Screening of Prey
Typically, insects and
other small bugs -- such
as flies, ants, and spiders -- are known to be prey for the
plants in the wild.
When the plant is in a vigorous growing condition, one often observes a band of
wet surface along the margin of the blades. This is due to secretions from the
nectar glands. Apparently, a sweet nectar is an important factor to allure prey,
along with visual attraction of the bright coloration of the trap interior.
Indeed, anyone who has ever observed an insect licking the nectar, as I have,
will be convinced that there is something almost intoxicating in the exudation
from the nectar glands.
With its mouth working on the inner margin of
the lobe where nectar is being served, an insect large enough in size to brush
against some of the trigger hairs ends up tripping the deadly trap. The trigger
hairs are so situated, in relation to the nectar
band, that, given a mature trap of 20-30mm in length, an insect less than
5mm or less is not likely to trigger the trap. Considering the amount of energy
needed for a tiny plant to close the trap, this preliminary screening of prey
large enough to make it worth the effort can be construed as an economic measure
of a sort. Lloyd cites a report showing that, of fifty closed traps examined,
only one contained the catch less than 5mm in length, and only seven less than
6mm in length. All the other catches were 10-30mm in length.
There are two phases in the trap closure. The
initial phase is characterized by a quite rapid movement of the trap lobes that
brings guard hairs on the edge of both lobes together, close enough to interlace
them. This will effectively entrap the prey of sufficient size inside the trap,
while leaving some open spaces between interlaced guard hairs for small er prey
to escape -- the second screening of prey, if you will --
before proceeding to the digestive phase.
Multiple Stimulation Requirement
It is well known
among growers that, in order to close the trap,
not one but two stimulations are required: either two different trigger hairs
must be each stimulated once, or a single trigger hair stimulated twice. This is
the plant's clever way of making sure that the prey about to be snapped has
reached the center of the trap before triggering the trap.
This delay strategy increases the chance of a successful catch. With each snap
consuming so much energy, the Venus
flytrap can not afford too many misses.
It is also observed that a mild rain usually does not trigger the trap.
Many experiments have been
conducted on this snap trap
behavior of the plant. In a normal condition, stimulating a trigger hair once
does not cause a trap movement. To initiate a successful closure, it is
necessary to stimulate two different hairs, or stimulate the same hair twice,
within a 20 seconds or so interval. If the two stimuli are given in a rapid
succession, a quite swift closure -- well under half a second -- immediately
follows. The longer the interval between two stimuli, the less rapid the closure
becomes. If it is within 20 seconds, a rapid trap closure usually occurs within
a few seconds. If the second stimulus takes place after a half minute or later,
however, the closure itself becomes extremely slow and multiple stimuli may be
required to complete the closure. On the other hand, in the height of a growing
season, if the temperature is 35 degrees C or higher, a trap closure may occur
by one stimulus only. It is also noted that the stimulation to the lobe part,
other than the trigger hairs themselves, particularly the area near the hairs,
does sometimes induce trap closure.
Studies have shown that sensory cells
responsible for triggering the trap are
located near the base of the trigger hair, at the indentation where bending
strains are most pronounced when hairs are touched. Action potentials have been
observed upon bending of the trigger hairs.
A sudden drop of the cellular pressure on the
inner surface of the lobes causes the imbalance to the higher pressure of cells
on the outer surface, thus precipitating a sudden closing
action of the trap.
The reopening phase, on the other hand, proceeds rather slowly, taking several
hours. Unlike the rapid closing phase, it is due to cell growth. A growth rate of
an activated leaf is higher than an undisturbed trap and a reopened lobe
measured to be several percent
larger than the original size.
The trap can be made to close by mechanical
stimulation to the trigger hairs. The trap reopens the next day if the trap is
empty, or only contains inanimate object with no nutritious value to the plant. Each trap can be "fooled" to close several
times before it reaches its growth maturity and ceases to function.
Digestion and Absorption
The initial phase of rapid closure is
followed by what is termed the narrowing phase. This second phase is pursued
only if the trap catches something nutritious to the plant, or if the stimulus
is continuously coming as would be the case if a live insect is captured. The
narrowing phase is a slower process which brings the margin
of two lobes tightly together.
Often the pressure exerted in this phase is strong enough to crush a soft-bodied
insect prey, thus possibly causing chemical stimulation.
As the lobes are tightly sealed, digestive
fluids are secreted from the digestive glands into the closed trap interior. The
prey, if still alive, will most probably be suffocated in the fluids. The
digestive secretions which is known to be initiated only by proper chemical
stimulation typically begins a day or so after the capture of prey, although
such protein-rich substances as egg-whites may often induce copious secretions in
a matter of a few hours. Digested material is then absorbed through the glands
and through the inner surface of the trap.
The digestive process, not unlike that of an
animal's stomach, lasts for a few days to a week, depending on the size of the
prey. When the digestion/absorption process is over, the trap (now dry) reopens,
revealing the chitinous remains of the prey. The wind and rain clean the
lobes, and the trap is ready again for another meal. Each trap is capable of
completing the whole digestive process two or three times at most before it ceases to function. Too
large a catch often results in the damage of the trap, as the trapped animal
begins to decay, causing the entire leaf blade to blacken and die out before the
digestion is complete -- an upset stomach, as it were.
In the early spring, a flower bud appears in
the rosette center. In a month or so, this develops into a tall scape (flower stem) bearing
many white flowers. A scape often reaches a
height of 20-30cm in nature, providing a possible spatial
separation of pollinators and prey. An actinomorphic flower (radially symmetric) with five
petals bloom in May through June in North Carolina. An
elegant, white flower is shot with green veins on the petal. Each flower
typically opens for 2-3 days.
Numerous black seeds fully mature by late July.
As the seed capsule dries,
the pressure from capsule shrinkage bursts the slippery, pear-shaped seeds
around the field.
In nature, the seeds germinate shortly after
the dispersal and tiny seedlings have a few months to prepare for the onset of
winter. In spite of A relatively small size of the plant, It takes 3 to 4
years for the seedling of the Venus flytrap to reach a flowering age.
The plant is said to live for 20-25 years.
Birth of flytraps. Two-day^
old. Germination begins as
seeds take up water and
swell. The embryonic root
then emerges from the seed
coat, from which sprout
Two-week old seedlings, 5 tnr" tall. As the root hairs anchor in the earth,
twin cotyledons --- seed leaves --- appear. These cotyledons have no traps
on them, but the leaf right after the cotyledons does have a miniature trap.
The Venus' flytrap matures from seedling to flowering age in 3"1* years.
In May through June, many white flowers bloom
at the tip of a tall flower stem rising from the center of the plant. Seeds
mature by mid-summer, and tiny Venus flytrap babies are produced. It takes 3-4
years for the seedlings to reach flowering age.
This build-up of a threshold potential before
a trap motion is actually triggered is considered advantageous for the Venus
flytrap. This ensures a successful catch in many cases, by properly positioning
the prey in the center of the trap plate before a trapping attempt, rather than
closing the trap prematurely when much of the insect's body may still be outside