The frenzy of scare stories by the news media about the pending invasion of the so-called “murder hornet” in May triggered an unnecessary panic as reports circulated about people swatting and spraying beneficial bees and just about anything else with wings that buzzes. The furor subsided after cooler heads — and more level- headed reporting — prevailed and authorities stressed that the four or so Asian giant hornets found in Washington state late in 2019 never established a beachhead. Even so, and despite the coronavirus pandemic, for a week or so, hornets occupied a big chunk of the nation’s collective mind.
Given the focus on these worrisome insects, it is a good time to note that there are hornets and there are hornets. Much, if not most, of the public is confused about what is and what isn’t a hornet. Or, more precisely, they are confused about what should and what should not be called a hornet. If misinformation about the subject displayed on a few pest control company websites is any indication, even some PMPs are not so sure.
It’s hard to blame them. Common names of creatures are often misleading, in spades for hornets and their kin. Scientifically speaking, for example, the so-called bald-faced or white-faced hornet — its face is neither bald nor white — that sparks so many calls to PMPs is not a hornet at all. It belongs to one of two genera of yellowjackets in the United States.
Among the many yellowjacket species in North America is the German yellowjacket, a European native introduced in the northeastern United States. Say that name to a German or any other European and likely you will get a quizzical response. In Europe, nobody uses the term “yellowjacket.” There, yellowjackets are simply “German wasps.”
WHAT’S A WASP? The term “wasp” itself is nothing more than a common name and one that covers a lot of ground. From an entomological standpoint, it is a generalization, rather abstract and loosely applied to a host of stinging insects in the scientific order Hymenoptera that are not ants or bees. Even that definition has flaws because some insects with the word “wasp” attached to their names cannot sting. The stinger is found only in females because it is a modified ovipositor, the tubular organ through which eggs are deposited. In species such as the ichneumon wasps, the ovipositor is modified to drill into wood, creating a hole nest, and incapable of stinging.
Many of the creatures that are called “wasps,” moreover, are not even kissing cousins but related only distantly. By most systems by which scientists describe wasp relationships, the cicada killer wasp is far removed from those such as yellowjackets and more closely related to certain bees, even ants. “The term ‘wasp’ is a common name that doesn’t represent a single evolutionary related group,” says Dr. Allan H. Smith-Pardo, an entomologist with the USDA’s Animal and Plant Health Inspection Service.
One of the reasons wasps can be so confusing is that there is an immense — even dazzling — variety among their plethora of species. There are potter wasps and paper wasps, bee wolves and spider (killer) wasps, cuckoo wasps and emerald cockroach wasps — and that’s just for starters.
Generally speaking, hornets are wasps, too. Of the approximately 27,000 species of insects that are loosely known by the name wasps, 22 are recognized by scientific classification as hornets, a common name scientists restrict to the genus Vespa.
Despite their relatively tiny number of species, identifying hornets gives fits even to scientists, largely because the color patterns and size of individuals of the same species vary so much that even experts play a name game with them.
SETTING THINGS STRAIGHT. To straighten out the mess, Smith-Pardo and colleagues recently published a paper in the journal Insect Systematics and Diversity that provides a cutting-edge key to identifying the world’s hornets, with abundant visual support. It leans heavily on the observable physical characteristics that facilitate distinguishing one species from another.
Knowing how to precisely identify hornets, and indeed all wasps, says Smith- Pardo, is a major asset for those involved in pest management and control. It decreases unnecessary elimination of species that are beneficial, by helping control agricultural pests, for example.
If the Asian giant hornet ever gets a foothold on these shores, knowing how to tell one hornet from another could truly pay off. It closely resembles the European giant hornet, which was introduced to the United States in the 1840s and now ranges from the East Coast to the Rocky Mountains. Not inconceivably, PMPs who know the difference could be the front line of defense against an invasion of these Asian stingers by being able to differentiate between the two look-alike species. (Although the European hornet can be a nuisance, by the way, it does destroy many harmful insects and even is protected in some parts of its native continent.)
Asia, European or whatever, says Smith-Pardo, “If it turns out to be a true Vespa, it is not a native.” That is because all hornets belong to the Old World, with one species in Europe and the rest in Asia, mostly the tropics and subtropics.
Delving deeper into the way scientists sort wasps can be a bit bewildering because the scientists whose job it is to classify living organisms continually tinker with what goes where on the tree of life. The placement of species on various branches are often rearranged and occasionally one classifier’s species might be another’s subspecies or even not exist at all. It seems to happen more frequently than usual with wasps, possibly because there are so many and they are so diversified. The cicada killer wasp, for example, has been shifted back and forth between two different families, as if scientists are not exactly sure of their place in the natural scheme of things.
All well enough, but if you want to get into the technical nitty-gritty of classification you must choose between two different ways of doing it. The older system is built on a hierarchy of organisms based on their shared characteristics and organized into groups such as families, subfamilies, genera and species. The European hornet is Vespa crabro and belongs to the subfamily Vespinae, with the yellowjackets, which totals 80 species including the hornets. By the way, the common names of the European and Asian giant hornet (Vespa mandarinia) are not recognized by the Entomological Society of America’s common names database. Newer is a system based on evolutionary biology that is bolstered by advances in genetics, animal behavior and other fields in which species are grouped by common ancestry.
Given the different ways of defining wasps, how many species exist depends on how one classifies them. Scientists fudge a bit by calling the family Vespidae, an assemblage of 5,000 species which includes yellowjackets, hornets and paper wasps, “true wasps.” A shared characteristic is folded wings when not flying.
SOCIAL V. SOLITARY. One group in this family probably accounts for most of the wasp control done by pest control companies. Yellowjackets, hornets and paper wasps are labelled “social wasps” because they live in colonies. Not only, as a group, do these wasps deliver a more painful zap than most but they forcefully defend their nests, emitting alarm pheromones that draw their fellows to mass attacks.
The majority of creatures called wasps, including mud daubers, cicada killers and spider hawks, are solitary. Each female solitary wasp builds her own nests and rears her own young, as opposed to social wasps, which construct the nest and care for young with a shared labor force of workers.
At a glance, it might seem as if the assemblages of burrows that cicada killers dig to house nest chambers — and which riddle many a lawn — are evidence of social living. They are not, however, because each female digs her burrow independently. It is just that female cicada killers naturally congregate where the soil is optimum for burrowing; loose and sandy soil is their favorite.
Typically, solitary wasps are parasites in one way or another. They disable prey and take it home for their young to feed upon. The cicada killer, for instance, stuns annual cicadas with a sting and hauls them to its burrow. After caching the catatonic cicada in a nest chamber within the burrow, the wasp lays her egg upon it. When the egg hatches, the larval wasp has a ready supply of fresh meat, as it were.
The cicada killer has a powerful sting but poses little threat to humans because it is not aggressive and does not defend its nest. Like most solitary wasps, the stinger is a weapon used to disable prey, not for defense, so they are not engineered to use it when threatened, although occasionally they do.
One of the enemies of the cicada killer seems to be a fuzzy, colorful insect called the velvet ant. It turns the tables on the cicada killer by laying its egg where its larvae can parasitize that of the cicada killer. The velvet ant, by the way, is not an ant at all. It is a flightless wasp.