The Most Dangerous Insect in the World
25 May 2015
In Japan, you will find the most dangerous insect in the world. The Japanese giant hornet is a subspecies of the world’s largest hornet, the Asian giant hornet also known as Vespa Mandarinia. It is a large insect and adults can be more than 4.5 centimeters (1.8 in) longer, with a wingspan greater than 6 centimeters (2.4 in). It has a large yellow head with large eyes, and a dark brown thorax with an abdomen banded in brown and yellow. The Japanese giant hornet has three small, simple eyes on the top of the head between the two large compound eyes. As the name implies, it is endemic to the Japanese islands, where it prefers rural areas where it can find trees to nest in. In Japanese it is known as ōsuzumebachi, the sparrow bee.
In Japan, beekeepers often prefer European honey bees because they are more productive than the endemic Japanese honey bees. However, it is quite difficult to maintain a captive hive of European honey bees, as the giant hornets are devastating to the beehives. Once a Japanese giant hornet has located a hive of European honey bees it leaves pheromone markers around it that quickly attract nest-mates to converge on the hive. An individual hornet can kill forty European honey bees in a single minute; a swarm of just 30 hornets can destroy a hive of 30,000 bees in just three hours. The hornets kill and dismember the bees, returning to their nest with the bee thoraxes, which they feed to their larvae, leaving heads and limbs behind. The honey and bee larvae are also taken to feed the hornet larvae.
Unlike the European honeybee, the Japanese honey bee can defend themselves against attacks. When a hornet approaches the hive to release pheromones, the bee workers will retreat back to the hive, leaving an opening to allow the hornet scout to enter. At a given point, the bees emerge from their hiding places in an angry cloud formation containing some 500 individuals. They form a tight ball around the hornet that acts like a convection oven: the bees vibrate their wings, generating heat via muscular exertion, and then direct the air warmed around them into the inside of the ball. This causes the interior temperature of the ball to rise to 47 °C. While significant, this high temperature alone is not sufficient to kill the hornet trapped in the bee ball. However the bees’ activity also increases carbon dioxide concentration inside the ball. The hornet’s ability to withstand heat decreases as carbon dioxide concentrations increase. So the 47 °C temperature becomes lethal to the hornets. Meanwhile, the honey bees can withstand temperatures of 48–50 °C under the same conditions, so the hornet is killed and the bees survive.
The Japanese giant hornet is large and can be very aggressive if provoked. It has a venom which is injected by the 6.25 mm-long stinger and attacks the nervous system and damages tissues of its victims. Tests with mice find the venom not to be the most lethal, having an LD50 (abbreviation for “lethal dose, 50%”) of 4.0 mg/kg, which compares to the deadliest wasp venom (to mice) by weight of Vespa luctuosa at 1.6 mg/kg. The potency of the sting is due to the relatively large amount of venom injected. Being stung is extremely painful and can require hospitalization. Asian giant hornet stings can cause anaphylactic shock in allergic people, and can still be lethal to people who are not allergic, provided the dose is sufficient. Advice in China is that people stung more than 10 times need medical help, and emergency treatment for more than 30 stings. The stings can cause renal failure. Thirty to forty people die in Japan every year after having been stung, which makes the Japanese giant hornet the most lethal animal in Japan.
This hornets attack honey bees every year in a particularly violent fashion, chewing their victims’ flesh into a powerful substance that boosts the hornet’s strength. It is common for a swarm of hornets to decimate a honeybee hive with ease.
For years the Vespa Mandarinia has lived among inhabitants in China and elsewhere across East Asia. Parts of Japan in particular have been home to significant populations for years. But they have never attacked like they are attacking now.
Emergency teams led by the fire department are working nest to nest in an attempt to destroy as many as possible. The government reports that more than 4,000 nests have been destroyed. But it is harder and harder to reach the more remote, rural hives. Accompanying one unit on a response call, the team was forced to trek on foot to the site. In full protective, the gear they used is a massive jerry-rigged torch to set the hive in flames until it was nothing more than a smoldering, charred remain.
“The hornets that survived have no more home,” said one member of the team. “They will die.”
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