Introduction
This article is the first in a series I’m calling “Wasp Wednesday”, a weekly feature wherein we explore the vast, incredible biodiversity of wasps! Today, I’ll be providing an overview of the order Hymenoptera, which is the insect group that contains all wasps. This article will set the groundwork from which the future Wasp Wednesday articles will be developed. For each following week, I’ll cover a particular wasp taxon in detail. Entomologists like me and others at the Frost Museum have made it our mission to collect, identify, and describe as many species as possible in order to provide humanity a more holistic view of life on Earth. By doing so, we get closer and closer to understanding how exactly our world works, and how humans are impacting its natural function. Through this Wasp Wednesday series, we hope to present these concepts and widen the lens through which wasps are perceived.
Diversity
The order Hymenoptera includes the sawflies, wasps, bees, and ants. Evolutionarily speaking, bees and ants are actually specialized wasps, as they themselves are descended from other wasps. The group contains over 150,000 living species, including around 8,000 species of sawflies, 20,000 species of bees, 12,000 species of ants, and over 100,000 species of wasps. These species are organized into over 90 families and over 8,000 genera. In North America, there are around 18,000 described species. Entomologists estimate that there are as many as three million species currently living on Earth, meaning only a tiny portion of hymenopteran diversity has actually been documented by science!
Biology
Hymenopterans are holometabolous, which means that they undergo complete metamorphosis and go through the egg, larva, pupa, and adult stages throughout their lives. Hymenopterans are most closely related to the other groups that undergo complete metamorphosis, which are order Lepidoptera (butterflies and moths), order Trichoptera (caddisflies), order Diptera (true flies), and clade Mecopteroidea (scorpionflies, fleas, and relatives).
Hymenopterans live many different lifestyles. Many prominent species are pollinators; while many assume that bees are the primary pollinators amongst the order, most wasps, and even many ants, serve as pollinators as well! Most adult wasps are nectar feeders, and will pollinate the plants they land on to consume their nectar. Some wasps, like the infamous yellow jackets, are polyphagous, meaning they eat many different kinds of food, including nectar, plants, and even other insects. Some species of hymenopterans are social, meaning they have a caste system that divides labor between individuals. Common examples of social hymenopterans are honeybees, bumblebees, and many species of ants.
Perhaps the most widespread lifestyle within Hymenoptera is that of parasitoids. Parasitoids lay their eggs within living host organisms, typically other insects, using an egg-laying organ called the ovipositor. When their eggs hatch, they eat the tissues of their host and pupate before eventually emerging as adults. The vast majority of hymenopterans are parasitoid wasps, and some entomologists believe that parasitoid wasps are the most diverse group of insects!
Classification
Members of Hymenoptera are united by several characteristics. They have two pairs of wings, except in individuals with modified or reduced wings such as ants. They also have a series of small, hook-like structures called hamuli on the hindwing that connects the wings together in flight. These structures are found almost exclusively on hymenopterans, although some groups of parasitic plant bugs also have them. Finally, all members of the order Hymenoptera have chewing mouthparts.
The higher classification of Hymenoptera is an issue of great debate within modern entomology. As a result, many sources retain the use of several groups that are considered evolutionarily inconsistent. These groups are paraphyletic, meaning they refer to groups of organisms that exclude other descendents of the same common ancestor. Because of this, paraphyletic groups are not accurate regarding their evolutionary past, and misrepresent how organisms have evolved. Paraphyletic groups make understanding the true classification of organisms difficult, as they lack consistency and prevent us from making predictions about the group’s natural history. In order to provide the most accessible explanation of the order Hymenoptera, several paraphyletic groups are described here. Names of paraphyletic groups are given in quotation marks (e.g. “Symphyta”). The figure below uses the example of birds and reptiles to demonstrate what a paraphyletic group is – birds and reptiles have traditionally been classified separately, but we now know that birds are actually derived from within reptiles! Because birds are excluded from “Reptilia”, the conventional classification of reptiles makes the group paraphyletic.
However, not every group of Hymenoptera is paraphyletic! By using molecular analysis in combination with examining insect morphology, we have demonstrated that many groups within Hymenoptera are monophyletic. For instance, “bees” is a monophyletic group, as are “ants”, “cuckoo wasps”, and many other hymenopteran lineages. Monophyletic groups include all descendents of a single common ancestor and allow us to better predict the life history of included organisms, including things like geographic distribution, and even things like what types of hosts they use.
The order Hymenoptera has historically been divided into two suborders: the “Symphyta”, which includes the sawflies, and the Apocrita, which includes the remainder of the group. These groups are distinguished based on the shape of the junction between the thorax and abdomen; in sawflies, the abdomen is broadly joined to the thorax, while in all other hymenopterans, the abdomen is petiolate, meaning it is joined to the thorax by a thin segment which gives a “wasp waist” appearance. This difference is partly the result of differential fusion of the subsegments that make up the thorax and abdomen. In Apocrita, the first true segment of the abdomen is joined with the thorax, meaning they no longer have a “true” abdomen and thorax. As a result, the term mesosoma, which means “middle segment”, is used to describe the thorax of members of “Apocrita”, and the term metasoma, meaning “last segment”, is used to describe the apocritan abdomen. The classification of Apocrita is a similar story; traditional classifications place “Parasitica”, the parasitoid wasps, and Aculeata, the stinging wasps, as two separated groups. Like Apocrita and “Symphyta”, Aculeata is actually nested within “Parasitica”, meaning yet again the classification does not accurately represent the evolution of the group. The figure below shows the true abdomen of sawflies as well as the superficial abdomen of apocritan wasps, including the segment of the abdomen that has become attached to the thorax.
In North America, the order Hymenoptera is currently represented by 80 families. The following schematic shows the current taxonomy and organization of the order Hymenoptera of North America. Paraphyletic groups are shown in bold and in quotation marks below.
ORDER HYMENOPTERA
Suborder “Symphyta”: Sawflies
- Superfamily Xyeloidea
- Family Xyelidae: Xyelid sawflies
- Superfamily Pamphilioidea
- Family Pamphiliidae: Leaf-rolling sawflies
- Superfamily Tenthredinoidea
- Family Argidae: Argid sawflies
- Family Cimbicidae: Cimbicid sawflies
- Family Diprionidae: Diprionid sawflies
- Family Pergidae: Pergid sawflies
- Family Tenthredinidae: Common sawflies
- Superfamily Cephoidea
- Family Cephidae: Stem sawflies
- Superfamily Siricoidea
- Family Anaxyelidae: Cedar incense woodwasps
- Family Siricidae: Horntail woodwasps
- Superfamily Xiphydrioidea
- Family Xiphydriidae: Xiphydriid sawflies
- Superfamily Orussoidea
- Family Orussidae: Parasitic sawflies
Suborder Apocrita: True wasps
- Clade “Parasitica”: Parasitic wasps
- Superfamily Stephanoidea
- Family Stephanidae: Crown wasps
- Superfamily Trigonalyoidea
- Family Trigonalidae: Trigonalid wasps
- Superfamily Evanioidea
- Family Aulacidae: Aulacid wasps
- Family Evanioidea: Ensign wasps
- Family Gasteruptiidae: Carrot wasps
- Superfamily Ceraphronoidea
- Family Ceraphronidae: Ceraphronid wasps
- Family Megaspilidae: Megaspilid wasps
- Superfamily Proctotrupoidea
- Family Heloridae: Helorid wasps
- Family Pelecinidae: Pelecinid wasps
- Family Proctotrupidae: Proctotrupid wasps
- Family Roproniidae: Roproniid wasps
- Family Vanhorniidae: Vanhorniid wasps
- Superfamily Diaprioidea
- Family Diapriidae: Diapriid wasps
- Family Ismaridae: Ismarid wasps
- Superfamily Platygastroidea
- Family Platygastridae: Platygastrid wasps
- Superfamily Cynipoidea
- Family Cynipidae: Gall wasps
- Family Figitidae: Figitid wasps
- Family Ibaliidae: Ibaliid wasps
- Family Liopteridae: Liopterid wasps
- Superfamily Chalcidoidea
- Family Agaonidae: Fig wasps
- Family Aphelinidae: Aphelinid wasps
- Family Azotidae: Azotid wasps
- Family Chalcididae: Chalcid wasps
- Family Encyrtidae: Encyrtid wasps
- Family Eriaporidae: Eriaporid wasps
- Family Eucharitidae: Eucharitid wasps
- Family Eulophidae: Eulophid wasps
- Family Eupelmidae: Eupelmid wasps
- Family Eurytomidae: Eurytomid wasps
- Family Leucospidae: Leucospid wasps
- Family Mymaridae: Fairy wasps
- Family Ormyridae: Ormyrid wasps
- Family Perilampidae: Perilampid wasps
- Family Pteromalidae: Pteromalid wasps
- Family Signiphoridae: Signiphorid wasps
- Family Tanaostigmatidae: Tanaostigmatid wasps
- Family Tetracampidae: Tetracampid wasps
- Family Torymidae: Torymid wasps
- Family Trichogrammatidae: Trichogrammatid wasps
- Superfamily Mymarommatoidea
- Family Mymarommatidae: Mymarommatid wasps
- Superfamily Ichneumonoidea
- Family Braconidae: Braconid wasps
- Family Ichneumonidae: Ichneumon wasps
- Superfamily Stephanoidea
- Clade Aculeata: Stinging wasps
- Superfamily Chrysidoidea
- Family Bethylidae: Flat wasps
- Family Chrysididae: Cuckoo wasps
- Family Dryinidae: Dryinid wasps
- Family Embolemidae: Embolemid wasps
- Family Sclerogibbidae: Sclerogibbid wasps
- Superfamily “Vespoidea”
- Family Formicidae: True ants
- Family Mutillidae: Velvet ants
- Family Myrmosidae: Myrmosid wasps (Sometimes also called velvet ants)
- Family Pompilidae: Spider wasps
- Family Sapygidae: Sapygid wasps
- Family Scoliidae: Mammoth wasps
- Family Chyphotidae: Chyphotid wasps
- Family Thynnidae: Thynnid wasps
- Family Sierolomorphidae: Sierolomorphid wasps
- Family Tiphiidae: Flower wasps
- Family Rhopalosomatidae: Rhopalosomatid wasps
- Family Vespidae: Yellow jackets, hornets, and allies
- Superfamily Apoidea
- Family Ampulicidae: Cockroach wasps
- Family Andrenidae: Mining bees
- Family Apidae: Cuckoo, carpenter, digger, bumble, and honey bees
- Family Colletidae: Plaster and cellophane bees
- Family “Crabronidae”: Crabronid wasps
- Family Halictidae: Sweat bees
- Family Megachilidae: Leaf-cutter bees
- Family Melittidae: Melittid bees
- Family Sphecidae: Thread-waisted wasps
- Superfamily Chrysidoidea
That’s all for this introduction into the order Hymenoptera! Look out for next week’s Wasp Wednesday, our first weekly showcase of various wasp specimens from the Frost Entomological Museum!
Find Out More About the Order Hymenoptera:
- On BugGuide: https://bugguide.net/node/view/59
- On iNaturalist: https://www.inaturalist.org/taxa/47201-Hymenoptera
References:
- Aguiar, A. P., Deans, A. R., Engel, M. S., Forshage, M., Huber, J. T., Jennings, J. T., … & Miko, I. (2013). Order Hymenoptera. In: Zhang, Z.-Q.(Ed.) Animal Biodiversity: An Outline of Higher-level Classification and Survey of Taxonomic Richness. Zootaxa, 3703(1), 51-62.
- Goulet, H., Huber, J. T. (1993). Hymenoptera of the world: An identification guide to families. Ottawa: Research Branch Agriculture Canada.
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