When a swarm of giant wasps attack a bee hive, the slaughter is brutal and swift.
After the scouts have identified the target hive, they descend en masse, killing defensive adult bees, occupying their nests and harvesting bee larvae to feed their own young bees. Marauders can destroy a hive in a matter of hours.
But bees are not defenseless against the so-called murder wasps, which are native to Asia but first appeared in the United States in 2019. Bees have their own survival strategies, including unique and fanatical warning signal movements that trigger defenses, which scientists have first documented.
Heather Mattila, an associate professor in the Department of Biological Sciences at Wellesley College, said: "When I heard them, I felt a heartfelt reaction because it was clear the bees were excited. ”
She described the warning signal, known as the "anti-predator pipe," as harsh and noisy, with varying duration and tone, similar to the screams, screams and terrified cries of mammals such as primates and mongooses when they are scared.
"Individual pipes have different durations, but workers string many of them together to form a longer signal. Their pitches also vary greatly, and in irregular ways, which makes them stand out. ”
She said the Asian bee (Apis cerana) appears to use this sound only when bumblebees attack the Vietnamese colonies the team studied. The study was published Tuesday in the Royal Society Open Science Journal.
"Our study shows that bees don't make sounds if there aren't any bumblebees. When a bee smells a bumblebee, this sound rarely makes a sound when reacting to a smaller bumblebee (but not a single bumblebee is seen). ), and when a giant bumblebee appears directly outside their nest, they make it the most," Mathila said by email.
"We haven't tested all the predatory scenarios that Asian bees might encounter, but this is good evidence that a real bumblebee attack is needed to trigger this response."
She said the signal was used to trigger some of the defense mechanisms that bees deploy in their arsenals to counter the murder of Bumblebee.
These include tactics such as fecal spotting — when bees collect animal droppings and smear it at the entrance of their colonies to repel and confuse bumblebees — and swarming to destroy enemies, known as bee balls.
The sphere involves hundreds of bees encircling the bumblebee in seconds, squeezing it and limiting its ability to breathe. Mathila explained that bees raise their body temperature to levels that are fatal to bumblebees.
Giant wasps are native to Asia but have recently been discovered in the United States
"They act like a collectively overheated python," she said.
The first U.S. sighting of an Asian giant bumblebee occurred in Washington State in 2019. How they got there from mainland Asia is unclear — but they could be on international container ships, cargo destined for the United States, or tourists visiting or returning. A total of 14 sightings and three nests were reported in Washington State where they were found in 2021.
Unlike Asian honeybees, Western bees (Apis mellifera) have not evolved any strategies to fend off giant wasps.
"American bees have no historical experience of evolving to defend against bumblebees. We don't expect them to react to the sounds that Asian bees make, and they don't perform many of the other important Bumblebee defense systems for bees," Mathilla said.
"When people use our American bees in Asia to keep bees, bumblebees attack them first because they are defenseless."