HORNETS ATTACK VISITING HONEYBEES
by Whit Gibbons
October 1, 2006
Who would win in a contest between Japanese giant hornets and honeybees?
Both can sting, but neither stings the other. The hornet crushes the honeybee
with its mandibles. The honeybee kills the hornet through overheating.
The winner depends on the homeland of the bees.
hornet is the only species of hornet known in which individuals gather
together and then attack other social bees or wasps en masse, fascinating
behavior displayed by an extraordinary predator. But one of its prey species
doesn't take too well to being bullied.
foraging strategy sounds like a four-phase military exercise. The first
step in the giant hornet's feeding sequence is raiding. Hornets fly solo
missions in search of nests of other social bees and wasps. Upon finding
a bee's nest, the lone hornet crushes individual bees in its jaws. The
dead bees are taken to the hornet nest to feed larvae. The solitary raider
returns to the bee colony a few times to take additional bees.
phase two, recruitment. The hornet rubs secretions from a special gland
onto the area surrounding the honeybee nest. The secretion is a pheromone,
a chemical compound used in communicating specific messages to its own
or other species of animals. Detecting a pheromone is like having a sixth
sense for chemical awareness. And the chemicals deliver information. In
this case the hornet's pheromone is a signal for other giant hornets to
amass and attack.
of the giant hornet flying in the area congregate as they sense the pheromone.
Then they attack. The well-named slaughter phase is under way. As many
as 40 European honeybees are killed per minute, and an attacking force
of 20 to 30 hornets can kill 30,000 bees in three hours. When the hornets
achieve such an impressive victory, they enter phase four: occupation
of the bee nest. For more than a week the hornets carry bee larvae and
pupae to their own nest as food for the hornet larvae.
If you like
to see the underdog win occasionally, stay tuned. The attack-and-conquer
approach in Japan works in favor of the marauding giant hornets when the
prey is a colony of European honeybees. This is the same species found
in America, where they were also introduced from Europe.
honeybees seem to be virtually defenseless against mass hornet attacks,
in part because they are oblivious to the impending onslaught. That is,
they are unable to detect the hornet pheromone and so are unaware of the
presence or plan of the hornets. But not all bees in Japan are the introduced
honeybees can detect the hornet pheromone, and they understand the message
being sent, something akin to deciphering an enemy code. The bees modify
their behavior by increasing the number of defenders at the nest. The
first hornet to attack is greeted by a swarm of more than 500 bees, which
form a large ball around the intruder. The ball of bees may stay intact
for up to 20 minutes, with the inner temperature of the ball reaching
116 degrees F, which is lethal to the hornet. The bees can withstand temperatures
up to 122 degrees, although some bees in the center die from hornet bites.
attacks occur in autumn when a surplus of food is needed to feed developing
hornet larvae. Sometimes the Japanese honeybees do not defeat the hornet,
if the surprise attack is carried out quickly, before the bees can mobilize.
Or if the bees have a small colony. But even then, most adult bees usually
escape and forfeit only the nest.
attacks and the differential response of nonnative and native honeybees
are a fascinating example of coevolution, in which two species evolve
in response to each other. The hornets have evolved a mechanism for acquiring
large quantities of baby food in a short time. Meanwhile, the native Japanese
honeybee evolved a counterstrategy, developing an effective defense against
the predator. The introduced European honeybee did not evolve in a system
requiring such a response. Hence, as a species they are essentially helpless
against the warlike tactics of the giant hornet.
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