Bees defend their hives against hornets with animal dung

News Desk
13 January 2021, Wed
Published: 03:05

Bees defend their hives against hornets with animal dung

Honeybees in Asia have it rough. Unlike their cousins in North America, where bee-eating hornets have arrived only recently, Asian bees are relentlessly hunted by these giant wasps. Constant attacks have kicked Asian honeybee evolution into high gear and resulted in the insects developing several defensive tactics besides simply using their stings. 

First, Asian honeybees build their nests as fortresses, with tiny entrances and tough walls. They also hiss aggressively at predators, to warn them they are being monitored. And, if that doesn’t work, they can swamp attackers in “bee balls”, which generate such heat that hornets inside are cooked alive. Now, a study published in PLOS ONE, by Heather Mattila of Wellesley College, in Massachusetts, shows that these bees have yet another trick up their sleeves: they shield their homes with dung.

Vespa mandarinia and Vespa soror are often called homicide hornets for a purpose. When scouts from these species discover a honeybee hive they land and go away with chemical markers close to the doorway. The scouts then return with as much as 50 of their kin to launch an assault. Armed with highly effective jaws and difficult body-armor that makes them proof against bee stings, the hornets besiege the hive’s entrance and attempt to tear it aside in order that they will pressure their method in. They’re attacked by guard bees as they achieve this, and are generally efficiently pushed away. However not all the time. Usually, they get inside and, as soon as there, every hornet kills 1000’s of bees. This slaughter paves the best way for the hornets to collect the true goal of the assault, the brood of larvae growing within the hive. These, they carry away to feed to their very own younger ready again on the nest. That obliterates the hive.

Hornet assaults are devastating to apiculture, so there may be nice curiosity from bee-keepers to find methods to assist their fees to preserve these predators at bay. When Dr Mattila’s co-author Gard Otis, of the College of Guelph, in Canada, realized from a beekeeper in Vietnam that bees there stick globs of water-buffalo dung on their hives after being visited by hornets, it subsequently piqued his curiosity.

That, in flip, led Dr Otis, Dr Mattila and their colleagues to go to Vietnam, the place they monitored 339 honeybee hives. They found that many of those hives have been certainly lined in globs of what appeared like manure and that almost all of those globs have been clustered across the hive entrance. After they monitored bees’ actions they found not solely that the bees have been gathering buffalo dung, but additionally that they often created globs from feces collected at a rooster coop and a dung pile in a pig enclosure. Additional monitoring of the hives confirmed that the bees shortly hooked up lots of globs of feces to their hives after hornet assaults.

To see whether or not this was a consequence of the chemical marks, Dr Mattila and her colleagues collected extracts from the glands hornets use to secrete the substances concerned. They then soaked some filter papers in these extracts and put bits of this material close to hive entrances. As management, additionally, they soaked some filter papers in ether and distributed these likewise close to the entrances of different hives.

The hornet extract provoked a powerful response. Inside a day of its arrival hive members created a mean of 15 close by globs. The ether prompted a mean of solely two. This implies bees are certainly sensitive to the marking techniques of hornets and put together for a possible assault accordingly.

To ensure the globs truly do assist bees to defend their hives, the crew recorded some assaults. A well-globbed-up hive, they discovered, decreased the period of time hornets spent attempting to interrupt in by 94%.

Why globs of feces repel hornets stays a puzzle. Dr Mattila speculates that dung accommodates compounds that antagonise the hornets in a roundabout way. Particularly, these can be defensive substances synthesized by the vegetation that buffalo, pigs and chickens eat. If that concept does certainly grow to be appropriate, then it appears Asian honeybees have invented an efficient type of chemical warfare. Source: The Economist