This review is what I am sending to New Scientist maga-
zine, a British weekly I review for regularly.  It will
be edited, I fear, and run, I hope, within a month.
 
Jonathan D. Beard
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Review of
 
The Hot-Blooded Insects:  Strategies and Mechanisms of
Thermoregulation.  By Bernd Heinrich.  Harvard Univer-
sity Press, Cambridge, 1993.  523 pp, with 10 photos
and 257 drawings, 80 by the author.  $75.00
 
 
 
In 1979, Bernd Heinrich wrote Bumblebee Economics, a
slim book explaining how bees fly in 0 degree weather
by warming their bodies up to 37 degrees, and maintain-
ing that temperature in flight.  Brilliantly written,
the book became a minor bestseller for Harvard Univer-
sity Press (which has kept it in print) and introduced
the then-novel concept of thermoregulation in insects
to a large audience.  Now Heinrich has returned with
The Hot-Blooded Insects, a book that shows that
thermoregulation research has reached middle-age:  it
is a stout 583 pages long, has a great deal more to say
about the topic, and lapses occasionally into harsh
criticism of other scientists.
 
Until very recently insects, like dinosaurs, were seen
as "cold-blooded" animals, content to assume whatever
temperature their environment offered, while robust
endotherms (animals maintaining a constant internal
temperature), like ourselves defend 37 degrees whether
in tundra or desert.  Not so, Heinrich has proven in
thousands of experiments:  arctic bees shiver with
their powerful flight muscles before taking off from
frost-covered ground, while their cousins in the Ari-
zona desert fly in 60 degree air by shedding heat
through their heads.
 
The Hot-Blooded Insects is above all a review of the
literature on thermoregulation for every group of in-
sects known to be capable of it--from dragonflies to
dung beetles.  In the 13 years since Bumblebee Econom-
ics, this literature has exploded, and any entomologist
or animal behaviorist will probably want to buy this
book just for the 58 pages of notes at the end.  Hein-
rich seems to have read every article about every
species that controls its temperature, and even pro-
vides thorough discussions of some insects--such as
fleas and springtails--that can NOT thermoregulate, yet
still coax impressive performance from their muscles.
 
But it is also a book about flight, the form of locomo-
tion that puts the greatest demands on muscles.  Heavy-
bodied insects--bees, dragonflies, beetles,
grasshoppers--that want to fly must maintain their
muscle-filled thoraxes at 40 degrees or higher; the
rapid contractions that create the familiar buzz of
such bugs can only be achieved by muscles warm enough
to contract at incredibly fast rates.  To reach flight
temperature, moths that fly at night must shiver these
muscles for several minutes in a nutritionally ex-
pensive warm-up, while many grasshoppers bask with
their dark bodies perpendicular to the sun's rays to
achieve the same internal temperature.  Flight conveys
such important advantages in finding prey, escaping
predators, and dispersing to new territories that Hein-
rich believes that it is the reason that insects have
"learned" to thermoregulate: "no...flying insect warms
up by basking or shivering except to fly," he writes.
 
Perhaps the most fascinating sections of The Hot-
Blooded Insects describe species which, instead of wor-
rying about warming up, have chosen niches in which
they can only survive at temperatures that would kill
almost anything else.  Cataglyphis bombycina, the "sil-
ver ant" of the Sahara, forages on the bodies of in-
sects killed by heat, and does so on sand as hot as 63
degrees.  Yet the ant's own "lethal temperature" is 54
degrees.  Every few seconds each ant must crawl up a
dry stalk of vegetation to "cool off" in the air above
the sand--or perish.  Skating on thin ice, indeed, but
the ants not only find their prey, they escape lizards
who can not tolerate quite that degree of heat.  Afri-
ca's deserts also host a beetle that literally runs
away from searing heat:  at 1 meter per second, it
cools from convection alone.
 
Heinrich is clear about his opinions.  In his section
on the "social thermoregulation" practiced by ant, bee
and termite colonies, he sternly rejects the "super-
organism theory" which posits a collective intelligence
at work.  And he is downright scathing in his attack on
scientists who believe that wings began as
thermoregulatory devices.  His candor is put to better
use in the "remaining problems" he lists at the end of
each chapter, admissions of what we still do not under-
stand.
 
 
 
Addendum for Bee-Line readers.  In addition to chapters
on bumblebees, tropical bees, and honeybees, there is a
very long chapter on social thermoregulation that goes
into detail on thermoregulation in honeybee swarms,
clusters and colonies within hives.  The discussion of
the swarm at low temperatures is among the most im-
pressive examples of Heinrich's mind at work.  The
temperature differences between the core bees and
mantle bees, and the behaviors associated with them, is
brilliantly worked out--this is where he demolishes the
"superorganism" theory.  There is only scant mention of
Africanized bees.