In 1951, John Wyndham published his successful novel,
‘The Day of the Triffids’,
which was also recorded for the radio,
made into a Hollywood film
and adapted several times for television series.
The novel is about a plant,
called a triffid,
which attacks and eats people.
It’s highly poisonous,
grows very tall and can move fast.
It also reproduces quickly and so,
in Wyndham’s book,
there were hundreds of thousands of them all over the world.
The plants seemed evil
because they realised where people were living
and waited for them to leave their homes.
Then they attacked.
‘The Day of the Triffids’ was a bestseller
and, in fact,
it is still in print today.
People love being afraid
and man-eating plants that attack by surprise
are a frightening idea!
We don’t know whether John Wyndham
used the real meat-eating plant,
the Venus flytrap,
as a model for his triffid.
Originally, it comes from a very small area
– within a sixty-mile radius of Wilmington,
North Carolina, in the United States,
although there is also a colony near Washington nowadays.
The Venus flytrap catches insects and spiders,
which are its main food,
with a trap on its leaves.
When its prey crawl along the leaves and touch a hair,
the trap closes
– but only if they touch a different hair
in the next twenty seconds.
This second-touch mechanism is a useful safeguard for the plant
against wasting energy
and means it can differentiate between its dinner and,
for instance, falling rain.
But if the insect comes into contact with a second hair
within twenty seconds,
the trap will shut with lightning speed.
It takes only about one-tenth of a second.
The edges of the leaves are covered with hairs,
which close to prevent large prey from escaping.
But the gaps between the hairs
also allow small insects to get away,
perhaps because digesting them would take more energy
than the plant would get from the small bodies.
If large prey moves inside the trap,
the hairs close more tightly
and digestion starts faster.
The closed leaves become a kind of stomach where acids kill
and start to digest the insect.
This lasts about ten days
and when the leaves open again,
there is almost nothing left.
The plant is then ready to catch more prey.
If, on the other hand,
the insect is so small that it can escape through the hairs,
the leaves re-open in twelve hours.
You probably think that the Venus flytrap
must be a big plant with many strong branches,
but it is actually quite small.
The tallest is only three to ten centimetres.
It also takes the plant as long as five years
to reach its full size.
But it can live for 20 to 30 years.
The most interesting question, of course,
is why this plant evolved in the way it did.
Most carnivorous plants choose their prey very carefully,
according to the kind of trap they have.
With the Venus flytrap,
prey is limited to beetles, spiders
and other crawling insects.
They probably came from another,
earlier family of meat-eating plants, called Drosera,
which use a sticky trap,
instead of one that suddenly closes.
We can’t be sure about the Venus flytrap’s family tree though,
because most fossils are from larger plants
which have wood in them.
The flytrap doesn’t.
Anyway, while Drosera catch smaller,
flying insects,
flytraps are only interested in larger,
crawling ones,
which usually walk over the plants
instead of flying to them.
Of course, larger insects are more likely
to get free from sticky surfaces too.
Carnivorous plants are found
in areas where the soil is poor.
Their carnivorous traps evolved to allow them
to get the important food
they could not take from the sandy,
wet earth where they grew.
According to research done in 1992,
there are only 35,800 plants in their natural habitat.
This suggests the plants might become extinct in the wild.
Perhaps because of their unusually violent
means of getting their daily diet,
Venus flytraps are popular plants
in people’s houses and gardens.
In fact, there are about five million of them
outside their natural habitat,
even though it is not easy to grow them
because they need conditions very similar to those in the wild.
Home cultivation may, therefore,
be the answer to worries about the plants becoming extinct.
But it’s worth remembering that John Wyndham’s triffids
also became a threat when they were grown
for their valuable oils.
It was only when farmers began to cultivate them on a large scale
that they fought back!