More ‘murder hornets’ are turning up. Here’s what you need to know

Two new specimens of Asian giant hornet have
turned up in the Pacific Northwest, suggesting that the invasive species made
it through the winter despite efforts last year to stamp out the menace to
North America’s honeybees.

A big, yellow-and-black insect found dead in a roadway near Custer, Wash., has been identified as the Asian giant hornet, or Vespa mandarinia, Sven Spichiger, an entomologist at the Washington State Department of Agriculture, announced May 29. It was “probably a queen,” he said, from a brood in a 2019 nest and now ready to found a colony of her own.

Canadian scientists have also confirmed their first giant hornet of 2020, a specimen spotted May 15 in Langley, British Columbia.

Dubbed the “murder hornet” to the annoyance
of entomologists, the predator earns its nickname from its proclivity to nab a
honeybee, bite off the bee’s head carried home to nourish young hornets.
Raiding parties of several dozen Asian giant hornets can kill whole hives
containing thousands of bees in a few hours.

Those are just some of the details that make
V. mandarinia the newsiest stinging
invader in years. It’s a fierce little predator, though not as apocalyptic as
“murder hornet” headlines have suggested.

Amid the uproar over the “new” hornets, a
few facts have been overlooked. For one, North America has previously had at
least one close call — not publicized at the time — with the world’s largest
hornet. Unlike the current sensational invasion, however, that early episode
had a happy ending, at least for the people and native insects of North America.
Not so much for the hornets. What’s more, these aren’t the only big, bad
hornets that have arrived at the borders of the continent.

Here’s what we know so far, and what we
don’t, about Asian giant hornets and the threats they pose.

Is this ‘invasion of the giant hornet’ really new?

Not entirely. What’s new for North America
is that last year scientists confirmed Asian giant hornets in the wild.

In September 2019, beekeepers tracked down and
destroyed a hornet nest about the diameter of a large grapefruit near a public
footpath in Nanaimo near Vancouver, Canada. Lone flying hornets also showed up
on both sides of the Canada-U.S. border, one at a hummingbird feeder near
Blaine, Wash.

But that wasn’t the Asian giant hornet’s first
touchdown on North American soil. California had an overlooked close call in 2016.
It wasn’t just some lone hornet hiding in a cargo container, says entomologist
Allan Smith-Pardo, now at the U.S. Department of Agriculture’s Animal and Plant
Health Inspection Service office in Sacramento, Calif. He was the scientist
charged with identifying any suspicious wasps or bees found in cargo or mail
nationwide. An inspector flagged an express package coming into the San
Francisco airport without any mention of insects in its labeling. Yet it held
some kind of papery honeycomb-like nest.

Giant hornet nest
After sightings of giant hornets on Vancouver Island in Canada, beekeepers tracked down this nest in a forested public park within the town of Nanaimo. A carefully suited-up team anesthetized the hornets with carbon dioxide and dropped them in alcohol, which killed them.Paul van Westendorp

The inspector wondered if someone was
smuggling in bees, which U.S. rules strictly ban in order to slow the influx of
viruses, predatory mites and other menaces. Smith-Pardo identified the package
as something even more dramatic: a whole nest of Asian giant hornets. “There
were no adults in the package, but plenty of pupae and larvae,” he says. A few
were still alive.

Instead of some bizarre attempt at
international sabotage, the package was probably a gourmet treat or even a
health aid. In their native home, “collected adults, pupae and larvae are
soaked in liquor,” says retired entomologist Jung-tai Chao, who studied paper
wasp social behavior at the University of Georgia as well as hornet ecology at
the Taiwan Forestry Research Institute. This “hornet liquor,” he says, is
believed to ease arthritis pain.

The 2016 hornet package was opened in a
secure room that keeps biological hazards from escaping. So that potential insect
disaster
became no more than a data point mentioned briefly on page 23 of
the May 2020 issue of Insect Systematics
and Diversity
. The overview looked only at hornets intercepted in
California during one decade, so there could have been other run-ins with
giants.

Is the Asian giant hornet the first hornet to try invading North America?

Far from it.

The hefty, though not record-setting, hornet
V. crabro spread from Europe into New
York state around the mid-19th century. Now found in scattered places east of
the Rockies, the European hornets nest in hollow trees and cozy nooks within
walls. Humans who blunder too close can get painful stings, says Bob Jacobson,
a retired entomologist in Cincinnati with a long-standing interest in hornets
and venoms. His cousin was stung by the species.

Like the Asian giant hornet, the European invader
attacks honeybees, and Jacobson has seen it go after bumblebees, too, as well
as yellow jackets and some other wasps. Unlike the new invader, though, a V. crabro hornet hunts alone. It picks
off a bee on a flower or at a hive but doesn’t gang up in groups for mass
slaughter of whole insect colonies.

Other hornets have also turned up in North
America without stirring public interest. That data search of interceptions in
California between 2010 and 2018 showed that inspectors stopped four other
species besides the giant. In Canada, just in 2019, entomologists identified two
different invasive hornet species, including V. soror, which is almost
as big as the Asian giant. Whether those arrivals could make a permanent home
remains to be seen.

Let’s back up. What are hornets, and why do people get so spooked by them?

True hornets are big, predatory, colony-forming
wasps, in the Vespa genus. Apart from
the European V. crabro, they’re native
to Asia. They need meat to feed their young, unlike honeybees, which collect
plant pollen as baby food. Another difference: A honeybee dies after its single-use
stinger rips out of its body. Hornets, however, are among the insects that can
sting and sting again.

The latest hornet identification
key
lists 22 species: striped and spangled in various browns and rusts,
gold and bluish-blacks. North America also has several native wasps popularly
nicknamed hornets. These natives, however, belong on a nearby but different
twig of the insect evolutionary tree.

Why do Asian giant hornets attack honeybees?

The Asian giant hornet doesn’t really specialize
in honeybees, says James Carpenter, a hornet specialist at the American Museum
of Natural History in New York City who is now marooned in Australia by travel
restrictions. For the early months of the one-year life cycle of a nest in
temperate climates, workers forage alone, often for beetles.

Toward the fall, however, the colony’s time
is running out, and workers face heavy demands for protein to raise the next
generation of queens that will take shelter during the winter and then start
their own colonies in spring. Workers band together in unique group-foraging
raids. Several dozen attack high-value targets, such as whole nests of
honeybees, other species of hornets, and yellow jackets.

The giant hornets “slaughter the adults,
then carry back the brood as food for their larvae,” Carpenter says. “Besides
the impact on honeybees, then, they might have an impact on native yellow jackets.”

Just how big is the Asian giant hornet, and how could beekeepers fight them?

V.
mandarinia
ranks as the world’s largest hornet. Queens can grow some 5 centimeters long, about the length of an
average-sized woman’s thumb. Wingspans can exceed 7 centimeters, not quite the
full width of a woman’s palm. Workers aren’t as big.

Beekeepers in Asia try to turn the giants’
size against them, says entomologist Jeff Pettis in Salisbury, Md., president
of Apimondia, an international federation of beekeepers’ associations. He’s
seen various kinds of traps and screening devices set up at hive entrances that
let a slim honeybee slip through but block big clunking hornets.

Not to be deterred, the hornets will lurk in
front of a blocked hive to pick off emerging bees. Pettis has even seen apiary
workers with a tennis or badminton racket chasing and “just whacking ’em.”

That’s not at all recommended, by the way. Giant
hornets have giant stingers, so it’s better to stay out of their way.

Wasps, hornets and bees size chart
The Asian giant hornet looms large among other wasps, bees and hornets. This image shows other species found in North America to scale.WSDA
Wasps, bees and hornets size chart
The Asian giant hornet looms large among other wasps, bees and hornets. This image shows other species found in North America to scale.WSDA

How bad is the sting?

There’s no real relationship between how dangerous
and how painful an insect’s sting is, says Justin Schmidt, of the Southwestern
Biological Institute and University of Arizona in Tucson.

The Asian giant hornet delivers a big dose
of fairly strong venom, he and colleagues determined after testing venom of four
kinds of Asian hornets on mice. The giant hornet species could zing the biggest
volume into its target, about 1,100 micrograms (dry weight) per individual
compared with around 150 from a dainty little honeybee. That hornet venom also
has a pretty strong knockdown power. Based on what venom did to lab mice in
tests, researchers say that just one full sting would have a 50 percent chance
of killing a decent-sized (270-gram) rodent.

The venom of Tetraponera ants from Malaysia has
“exquisite lethality,” but the sting isn’t very painful, Schmidt noted in Toxins in 2019. Schmidt has spent
decades developing a ranking system for stings by allowing
himself to be stung
(SN: 7/24/16),
Even though he has personal data on more than 80 insects, the Asian giant
hornet isn’t one of them. (So far.) From talking to various colleagues who have
been stung, however, he estimates that it’s equivalent to three to 10 yellow
jackets stinging simultaneously. That’s painful, but “not the end of the
world,” he says. What ranks at roughly 10 times more painful in his view are
bullet ants.

Pain aside, how dangerous will this hornet be for people?

A much-quoted number from a 1986 paper puts
Japan’s death toll for people stung by V.
mandarinia
at around 40 to 50 people per year. That includes people with
allergies to insect venom. (Estimates vary, Jacobson says, but notes a paper
reporting 1 percent to 3 percent.)  The
less-quoted parts of the report from Japan, however, point out that of the 14
people hospitalized for stings and discussed in the paper, those with fewer
than 50 stings had a good chance of surviving.

Chao, who contributed a case report to that
paper, was stung himself while out with his students collecting a large V. mandarinia nest.  He’s allergic to stings. “Unfortunately I did
not have my antihistamines with me,” he says. He was rushed to a hospital,
where after injections and a few hours’ observation, though, he was released.

If this hornet gets established, will people need to stay indoors to survive the invasion?

That’s not the way Paul van Westendorp sees
it.

As the principal beekeeping specialist for
the province of British Columbia, he received the first giant Asian hornet
specimens from beekeepers last year and knows how much damage the hornets can
do. Raiding parties literally leave heaps of headless honeybees around a hive
during a takeover to steal the young.

To put it in perspective, Asian giant hornets
perch at the apex of major insect predators. “Apex predators are maybe very
fierce in what they can do, but there are only a few of them around,” he says.

So, for most people the odds of ever coming across one are low.  “On a beautiful, hot summer day, one will normally have no hesitation to for a nice swim in the ocean — even if we recognize that there are orcas out there,” van Westendorp says.

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