Can't take the heat; don't enter the nest.

Japanese honeybees have devised a defensive strategy worthy of the best pro football coaches. In fact, this ploy accounts for Apis cerana japonica's impressive record of protecting its nest against attacks by the giant hornet, Vespa mandarinia japonica.

One might think that the honeybees sting their foes to death.

Nope. They tackle the hornets' offensive linemen, then use body heat to wipe them out, assert Masato Ono and his coworkers at Tamagawa University in Tokyo.

Upon finding a honeybee nest, a hornet kills a few of the bees and takes them home to its young. The forager usually manages to repeat this hunting trip successfully a few times. Then it makes a fatal mistake: It rubs a pheromone on the hive, signaling other hornets to attack the nest, the team reports in the Sept. 28 Nature.

However, the honeybees also detect the pheromone. In response, more than 100 workers go to the entrance of the nest to lure their foes inside. Then, as many as 500 bees tackle each hornet, forming a ball around it. The bees vibrate and raise the temperature of the ball to a killer 47oC for about 20 minutes, the researchers find. The honeybees can withstand temperatures up to about 50oC, but not so hornets.

Such an intricate defense mechanism evolves as an arms race between predator and prey, notes Robert L. Jeanne of the University of Wisconsin, Madison. No other insect that he knows of kills with heat.

The honeybee also uses this hot tackle strategy against the hornet V. simillima xanthoptera, although fewer workers are needed to do the job, the Japanese researchers found in earlier studies.

Hornets stage mass attacks only in the fall, when they have many mouths to feed. "This food pressure may force the hornet into high-risk foraging," the team suggests.

Sometimes the hornets stage successful coups, particularly if they can invade the nest before their front line is destroyed. In these cases, they take over the nest and collect the bees' larvae and pupae.

When the researchers put a piece of paper that smelled of the hornet pheromone outside a Japanese bees' nest, 50 to 100 of the insects attacked the paper. However, immigrant European honeybees (Apis mellifera) in Japan failed to respond to the scented paper, the team reports. They also failed to mount a timely defense against the invader. Indeed, 20 to 30 hornets can kill a colony of 30,000 bees in 3 hours.