126
I
nsects are usually described as
“cold-blooded,” or ectotherms.
Unlike mammals and other
“warm-blooded” endotherms,
animals that maintain their body
temperature at a more or less
constant level, insects have a
variable body temperature that
changes with their environment.
In the early 19th century,
however, British entomologist
George Newport discovered that
some moths and bees raise the
temperature of their thorax (the
central part of the body, to which
wings and limbs attach) above that
of the surrounding air by rapidly
flexing their muscles. It is nowknown that many insects are
heterotherms, maintaining different
temperatures in different parts of the
body, and are sometimes far warmer
than the ambient temperature.The right temperature
The main challenge facing insects
is how to get warm enough to fly
but cool enough not to overheat.
German–American entomologist
Bernd Heinrich explained in 1974
how moths, bees, and beetles could
continue to function by controlling
their own temperature. He realized
that insects’ thermal adaptations
do not differ as much from those of
vertebrates as had been thought.
Most flying insects have higher
metabolic rates than other animals
but their small body size means they
lose heat rapidly, so they cannot keep
their temperature constant at all
times. The minimum temperature
that allows an insect to fly varies
from species to species, but the
maximum temperature falls within
104–113°F (40–45°C). To prevent
overheating, insects can transfer
heat from the thorax to the abdomen.
Many larger flying insects would
remain grounded if they were not
able to increase the temperature of
their flight muscles. These insectsIN CONTEXT
KEY FIGURE
Bernd Heinrich (1940 –)BEFORE
1837 In the UK, George
Newport observes that flying
insects are capable of raising
their body temperature above
the ambient temperature.1941 Danish researchers
August Krogh and Eric
Zeuthen conclude that the
temperature of an insect’s
flight muscles just before
takeoff determine the muscles’
rate of work during flight.AFTER
1991 German biologist Harald
Esch describes how muscle
“warm-up” plays a role in brood
incubation and colony defense
as well as flight preparation.2012 Using infrared
thermography, Spanish
zoologist Jose R. Verdu shows
how some dung beetle species
heat or cool their thorax to
improve flight performance.ALL BODILY ACTIVITY
DEPENDS ON
TEMPERATURE
THERMOREGULATION IN INSECTS
In insects... the active
flight muscles... are,
metabolically, the most
active tissues known.
Bernd HeinrichUS_126-127_Thermo-regulation_in_insects.indd 126 12/11/18 6:24 PM