88
percent of change in Soay
sheep size attributed to
environmental factors
Enemy hornets
suffocate within
honeybees’ ball
Heat may boost vulnerability
to carbon dioxide increase
By Rachel Ehrenberg
Call it death by a thousand breaths.
When hundreds of honeybees envelop
a giant, predatory hornet in a ball, the
bees aren’t just putting on the heat, as
researchers had thought. Carbon dioxide levels spike along with temperature,
fingering suffocation as the hornet’s
cause of death, scientists report in an
upcoming Naturwissenschaften.
Bees inside the ball can apparently cope
with the smothering heat and low oxygen
levels, but the high temperature appears
Stingers are lousy weapons against the exoskeleton of an attacking hornet. But
by forming a ball (above), bees can kill a hornet with heat and with a spike in CO2.
to make giant hornets, Vespa mandarinia
japonica, less tolerant of cranked-up carbon dioxide levels. The concentration of
CO2 in the bee ball–enclosed air increases
to about 3. 6 percent after the ball forms,
dropping sharply to lower levels five minutes later, report Michio Sugahara and
A grazing diet for duck-billed dinos
frOm TOp: m. SugAHArA, f. SAkAmOTO; m. purnell/univ. Of leiceSTer
Duck-billed dinosaurs may have been the sheep of their ecosystems. patterns of tiny
scratches (shown) in the fossilized teeth of Edmontosaurus, a type of hadrosaur, suggest the dinos had more complex jaw movements than previously thought and may
have eaten grasslike plants, researchers report online June 29 in the Proceedings
of the National Academy of Sciences. Dinosaur jaws were simple hinges that allowed
biting but didn’t allow the side-to-side motions that mammals use to grind food, so
it was unknown how hadrosaurs, the dominant plant-eating vertebrates of the late
cretaceous, chewed plant material. looking at the direction of the most dominant
scratches, study coauthor mark purnell of the university of leicester in england and
his colleagues conclude that Edmontosaurus probably had hinges in its upper jaw,
allowing the top teeth to flare out as the mouth closed. The upper teeth would have
scraped against the bottom ones, grinding food and creating the micrometer-sized
scratches. The absence of pits and chips on the teeth suggests that Edmontosaurus
may have eaten grasses rather than tree parts, questioning accepted ideas about hadrosaurs’ role in the ecosystem, the researchers say. —Jenny Lauren Lee
Fumio Sakamoto, both of Kyoto Gakuen
University in Japan.
The researchers taped anesthetized
giant hornets to gas detectors and thermometer probes to measure CO2 concentrations and temperatures inside bee
balls. When the probes touched open bee
nests, the bees formed balls around the
hornets. All 24 test hornets died within
10 minutes of bee ball formation, the
team reports. Hornets bore no sign of
stings, pointing to smothering as the
cause of death.
The spike in CO2 might be just a metabolic by-product of the frenetic activity of the bees. But, says Stan Schneider
of the University of North Carolina at
Charlotte, bees might regulate this
“panting,” perhaps in response to odor or
behavioral cues from the giant hornets.
“The specificity of the behavior suggests
a very long coevolution in this predator-prey relationship,” Schneider says.
Although ball forming is unusual
among bee species, coordinated defensive behavior is not, says entomologist
P. Kirk Visscher of the University of
California, Riverside. Giant honeybees
form rippling waves en masse, startling
predators ( SN: 10/11/08, p. 10). There are
even bees that mount a collective attack
by yanking individual hairs on the enemy’s body. “It’s not like being stung by
a swarm, but it is still pretty annoying,”
Visscher says. s
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