Hot on the heels of the news that pandas like to smear horse manure all over themselves to keep warm, comes new research showing honey bees are also in the dung application business.
But unlike the pandas, it is not a way for the bees to keep warm, but rather to fend off the attacks of vicious giant hornets.
“This study demonstrates a fairly remarkable trait these bees have to defend themselves against a really awful predator,” said lead author professor Heather Mattila of Wellesley College in Massachusetts.
The study casts light on the dangers honeybees in the US now face following the arrival of giant hornets closely related to those in Vietnam.
The invasive “murder hornets”, (Vespa mandarinia) which have been documented in the US this year, also attack bee hives, and the researchers say American bees have not had time to develop the means to keep the hornets at bay.
Giant hornets can grow to over 2.5 inches (6.4cm) long and pack about seven times as much venom in a single sting as an ordinary honeybee.
The Asian hornet and so-called murder hornet, are the only kind of hornets which actively recruit their nestmates in organised attacks on bees which can lead to “nest breaches”, the research team said.
The hornets raid the nests, killing the bees and carrying away larvae and pupae to feed their own developing brood.
Professor Gard Otis, who has studied honeybees in Vietnam for decades, said the hornets could ultimately carry out similar honeybee hive raids in North America.
Professor Mattila said because the bees in North America and Canada lack the unique dung defence system developed by Vietnamese bees, beekeepers would have to rely on destroying the hornets’ nests, or hope that climate or other factors will limit the hornets’ spread.
Referring to Apis mellifera, the honeybee species commonly found in Canada, professor Mattila said: “They haven’t had the opportunity to evolve defences. It’s like going into a war cold.”
The project began when professor Otis asked beekeepers in Vietnam about dark spots he’d seen at hive entrances.
As part of a successful beekeeping development project funded by the Canadian government, he ran fall workshops from 2007 to 2011 in rural villages with high levels of poverty.
During one visit, an experienced beekeeper explained the substance was buffalo dung. All the beekeepers professor Otis worked with linked these hive spots with hornets.
“Dung collection is a behaviour never previously reported for honeybees, and no one had studied the phenomenon,” he said.
To study how bees reacted to the availability of different animals’ ordure, the researchers gathered dung from water buffalo, chickens, pigs and cows, and placed it in mounds near an apiary.
By the end of the day, some 150 bees had visited the piles of dung, with the researchers noting the bees had collected more of the “odoriferous manure” of pigs and chickens.
The team marked individual bees to identify them at their hives. Minutes later, they recorded videos of the marked bees applying the material at nest entrances.
The hornets spent less than half as much time at nest entrances with moderate to heavy dung spotting as they did at hives with few spots, and they spent only one-10th as much time chewing at the hive entrances to get at the bees’ brood.
They were also less likely to launch mass attacks on the more heavily spotted hives.
The scientists are unsure exactly what deters the hornets, although they suspect the insects are repelled by the unpleasant aroma of the excrement.
Dung may also mask odours emitted by the bees, they suggested.
To further understand the hornets’ behaviours, the researchers extracted the chemical pheromone applied by hornets when marking their target hive.
When the pheromone was applied to the bees’ entrance, it prompted honeybees to apply dung to the hive.
The team said the study is the first to document the use of tools by honeybees.
However, many scientists disagree over whether certain animals – let alone insects – use tools.
To qualify as tool users, animals must meet several criteria, including using an object from the environment – in this case, dung.
The bees clearly use the material to alter the hive with purpose, professor Otis has said.
The fact they shape and mould it with their mouth parts meets the test of holding or manipulating a tool, he said.
Beekeepers in Vietnam normally control hornets by standing guard and swatting away individuals, preventing them from escalating their attacks.
“If you allow them, a group of hornets assembles, attacks the colony and takes over. The beekeepers control them every day by moving among their hives and whacking hornets.”
Professor Otis said he was terrified at first about working near the giant hornets. Defensive hazmat suits typically worn when studying stinging insects in other countries were impracticable in Vietnamese heat, he said.
But within a few days, the team learned the hornets were not defensive when they were in the apiary and away from their own nests.