You should spend about 20 minutes on Questions 28-40, which are based on Reading Passage 3 below.
A
The glow-worm belongs to a family of beetles known as the Lampyridae or fireflies.
The fireflies are a huge group containing over 2000 species,
with new ones being discovered all the time. The feature which makes fireflies and
glow-worms so appealing is their ability to produce an often dazzling display of
light. The light is used by the adult fireflies as a signal to attract a mate, and
each species must develop its own 'call-sign' to avoid being confused with other
species glowing nearby. So within any one area each species will differ from its
neighbours in some way, for example in the colour or pattern of its light, how long
the pulses of light last, the interval between pulses and whether it displays in
flight or from the ground.
B
The firefly’s almost magical light has attracted human attention for generations. It
is described in an ancient Chinese encyclopaedia written over 2000 years ago by a
pupil of Confucius. Fireflies often featured in Japanese and Arabian folk medicine.
All over the world they have been the inspiration for countless poems, paintings and
stories. In Britain, for example, there are plenty of anecdotes describing how
glow-worms have been used to read by or used as emergency bicycle lamps when a
cyclist's batteries have failed without warning. Early travellers in the New World
came back with similar stories, of how the native people of Central America would
collect a type of click beetle and release them indoors to light up their huts.
Girls threaded them around their feet to illuminate the forest paths at night.
Fireflies very similar to those we see today have been found fossilised in rocks
which were formed about 30 million years ago, and their ancestors were probably glowing long before then.
It is impossible to be sure exactly when and where the first firefly appeared. The highest concentrations of firefly species today are to be found in the tropics of South America,
which may mean either that this is where they first evolved, or simply that they
prefer the conditions there.
Wherever they first arose, fireflies have since spread to almost every part of the
globe. Today members of the firefly family can be found almost anywhere outside the Arctic and Antarctic circles.
C
As with many insects, the glow-worm's life is divided into four distinct stages:
the egg, the larva (equivalent to the caterpillar of a butterfly), the pupa (or
chrysalis) and the adult. The glow-worm begins its life in the autumn as a pale
yellow egg. The freshly laid egg is extremely fragile but within a day its surface
has hardened into a shell. The egg usually takes about 35 days to hatch, but the exact time varies according to the temperature,
from about 27 days in hot weather to more than 45 days in cold weather. By the time
it is due to hatch, the glow-worm's light organ is fully developed, and its glow
signals that the egg will soon hatch.
After it has left the egg, the larva slowly grows from a few millimetres into the
size and shape of a matchstick. The larval stage is the only time the insect can
feed. The larva devotes much of its life to feeding and building up its food
reserves so that as an adult it will be free to concentrate all its efforts on the
task of finding a mate and reproducing. Throughout its time as a larva,
approximately 15 months, the glow-worm emits a bright light. The larva's light is
much fainter than the adult female's but it can still be seen more than five metres
away.
In the final stage of a glow-worm's life, the larva encases itself in a pupa) skin
while it changes from the simple larva to the more complex adult fly. When the adult
fly emerges from the pupa the male seeks a female with whom it can mate. After
mating, the female lays about 120 eggs. The adult flies have no mouth parts, cannot eat and therefore only live a few days.
When people talk of seeing a glow-worm they normally mean the brightly glowing adult
female.
D
In some countries the numbers of glow-worms have been falling. Evidence
suggests that there has been a steady decrease in the British glow-worm population
since the 1950s and possibly before that. Possible causes for the decline include
habitat destruction, pollution and changes in climate. Thousands of acres of
grassland have been built upon and glow-worm sites have become increasingly isolated
from each other. The widespread use of pesticides and fertilisers may also have
endangered the glow-worm. Being at the top of a food chain it is likely to absorb
any pollutants eaten by the snails on which it feeds. The effect of global warming
on rainfall and other weather patterns may also be playing a part in the
disappearance of glow-worms. A lot more research will be needed, however, before the causes of the glow-worm's gradual decline are clear.
E
Although glow-worms are found wherever conditions are damp,
food is in good supply and there is an over-hanging wall, they are most spectacular
in caves. For more than 100 years the glow-worm caves in New Zealand have attracted millions of people from all over the world.
The caves were first explored in 1887 by a local Maori chief, Tane Tinorau, and an
English surveyor, Fred Mace. They built a raft and, with candles as their only
light, they floated into the cave where the stream goes underground. As their eyes
adjusted to the darkness they saw myriad lights reflecting off the water. Looking up
they discovered that the ceiling was dotted with the lights of thousands of
glow-worms. They returned many times to explore further, and on an independent trip
Tane discovered the upper level of the cave and an easier access. The authorities
were advised and government surveyors mapped the caves. By 1888 Tane Tinorau had
opened the cave to tourists.