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See also: Evolution by natural selection 24–31 ■ Ecophysiology 72–73
■ Animal ecology 106–113 ■ Organisms and their environment 166THE VARIETY OF LIFE
“quiver” the muscles that control
the upbeat and downbeat of the
wings to generate heat before
taking off. Once flying, the muscles
use large amounts of chemical
energy but only some of it is used
to beat the wings; the rest becomes
more heat. This, combined with the
warmth of direct sunlight, means
a flying insect risks overheating.
To solve this problem, many
species have a heat-exchange
mechanism that shifts excess heat
from the thorax to the abdomen,
allowing the insect to maintain
a steady temperature in its thorax.Range of techniques
By changing the angle of their
wings, butterflies control their body
temperature. When they are trying
to warm up, holding their wings
wide open maximizes the amount
of sunshine falling on them. When
they are trying to cool down, they
move into shade or angle their
wings upward so that less direct
sunlight shines on their surface.Other insects use even more
remarkable methods to regulate their
body temperature. When a mosquito
drinks the warm blood of a mammal,
this raises its body temperature. To
compensate, it produces droplets of
fluid that are kept at the end of the
abdomen; evaporative cooling of
these droplets lowers the insect’s
temperature. Dung beetles construct
balls of dung in which females lay
their eggs. Some dung beetles are
able to raise the temperature of their
thorax so they can roll heavier balls.
The range of thermoregulation
techniques shows how life forms
evolve to better fit their environment.
They can also inspire technology:
arrays of solar panels angled to
track the Sun capture maximum
amounts of solar radiation—just like
butterfly wings. ■Heat regulation
Honeybees are renowned for
controlling the temperature
of their hive. When it gets too
hot, they ventilate it by using
their wings to fan the hot air
out of the nest. When it gets
too cold, the bees generate
metabolic heat by rapidly
contracting and relaxing their
flight muscles. They also use
heat as a defense mechanism.
Japanese giant hornets are
fierce predators of honeybees.
Capable of killing large
numbers quickly, they pose a
serious threat to bees’ nests.
Hornets begin their attacks by
picking off single honeybees
at the entrance to the hive.
However, Japanese honeybees
defend themselves with
self-generated heat. If a hornet
attacks, they swarm around it,
vibrating their wings to raise
their collective temperature.
Since the hornet cannot
tolerate a temperature above
114.8°F (46°C) whereas the
bees can survive at almost
118.4°F (48°C), the attacker
eventually dies.A tortoiseshell butterfly feeds on
a dandelion. Most butterflies can angle
their wings upward in an attempt
to cool down, in a process called
behavioral thermoregulation.This Japanese giant hornet is
raiding nursery cells in a bees’
nest in Hase Valley, Japan. Hornets
seek to devour the bee larvae
inside the cells.US_126-127_Thermo-regulation_in_insects.indd 127 12/11/18 6:24 PM