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Family Ichneumonidae - Ichneumonid Wasps

Wasp - Therion morio Wasp - Banchus Ichneumon Wasp - Dusona small wasp - Gelis - female Hover fly parasite - Diplazon laetatorius - female Ichneumon Wasp - Trogus pennator Thing - Ophion - male Pimplinae? - Pimpla pedalis - female Megarhyssa sp. - Megarhyssa macrurus - female
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Hymenoptera (Ants, Bees, Wasps and Sawflies)
No Taxon ("Parasitica" - Parasitoid Wasps)
Superfamily Ichneumonoidea (Braconid and Ichneumonid Wasps)
Family Ichneumonidae (Ichneumonid Wasps)
Other Common Names
Ichneumon Wasps (note that this name may cause confusion with the genus Ichneumon so may be inadvisable to use)
Darwin Wasps (Source) (note that this name is not universally accepted among hymenopterists and has received its share of pushback as the parasitism that befuddled him is now known to be shared among numerous families)
Synonyms and other taxonomic changes
The family was revised by Henry K. Townes in the 1960s and 1970s. Some of his names are no longer in use or have changed meaning, due to conflicts with the International Code of Zoological Nomenclature or to advances in taxonomy. Many earlier comments within BugGuide, and much old literature, used Townes' names & concepts, such as Gelinae (now Cryptinae and Phygadeuontinae) and Ephialtinae (now scattered within Pimplinae). See summary of the history of Townes' classification.

This site follows the classification of Wahl(1) and not Townes
Explanation of Names
Ichneumonidae Latreille‎, 1802‎
from the Latin ichneumon, from the Ancient Greek ἰχνεύμων ('tracker') + -idae (taxonomic family suffix)
Numbers
~5,000 described spp. in almost 500 genera in the Nearctic Region, possibly 3,000 more undescribed; arguably, the largest animal family, with the estimated 60,000 species worldwide(2) (up to 100,000, according to some estimates(3)).

A few minor subfamilies(3) are not yet in the Guide:
Diacritinae (Holarctic; 3 genera worldwide, 2 spp. in 2 genera in NA)
Microleptinae (Holarctic; a single genus represented in NA by 2 spp.)
Phrudinae (worldwide except Australian; 13 genera worldwide, 4 represented in NA by 6 spp.)
Stilbopinae (Eurasia and the Americas; 24 spp. in 3 genera worldwide; represented in NA by Stilbops latibasis) (Townes 1989 Revision can be found here.)
Size
3-40 mm (not including antennae or ovipositor)
Identification
The majority are small species, with a narrowed "wasp waist" but as parasitoid wasps differ from the stinging wasps (Aculeate) in that the ovipositor is not modified into a sting. The antennae are long, usually with at least 16 segments and at least half the length of the body. They are generally most recognizable by their wing venation (see comparison of typical wing venation by Washington State University): two recurrent veins; 2nd submarginal cell small or lacking; base of cubital vein lacking, 1st submarginal and 1st discoidal cells fused as a discosubmarginal cell. The resulting vein structure is often noted for its "horse head" shape. Ovipositor length varies tremendously, from the very short ovipositors of the Ichneumoninae and Ophioninae to those longer than the body found in Rhyssinae.

Exceptions: The exceptions to wing venation trends are the ichneumonid subfamily Hybrizontinae, which has a vein separating the 1st discal and submarginal cells and lacks the second recurrent vein (2m-cu), and the braconid subfamily Apozyginae, which possesses a the second recurrent vein (2m-cu).

     
Typical ichneumonid wing venation (left) and the modified venation of Hybrizontinae (Hybrizon).

Ichneumonid wasps vary greatly in size and color: many are uniformly colored, from yellowish to black, while others are brightly patterned with black and brown or black and yellow; many have the middle segments of their antennae yellowish or whitish, while others are entirely blackish or brownish.

Ichneumonids are notoriously hard to identify: aside from the sheer number of species, there are numerous cases of distant relatives that appear almost identical. Any identification based solely on comparing images should be treated as suspect unless an expert has said there are no lookalikes for the species or group in question.

Key to subfamilies and general description in(3)
Range
Worldwide(1)
Habitat
Common almost everywhere
Food
a great variety of hosts (mostly immature stages) is used, though most species attack only a few host types; some infest spiders and other non-insect arthropods(4)(5)
Life Cycle
Many hibernate as adults, usually under loose bark of fallen trees(6)
Remarks
Many species help control insect pest populations and some have been introduced for that purpose.
No common name, Bathyplectes curculionis. From the Palaearctic, 1911, to control the Hypera postica (Alfalfa Leaf Weevil)
No common name, Bathyplectes infernalis. From the Palaearctic to control Donus zoilus (Clover Leaf Weevil)
No common name, Collyria coxator. From the Palaearctic, to control Cephidae Cephus pygmaeus, Janus integer
No common name, Eriborus terebrans. From the Palaearctic, from 1927 through 1940, to control Ostrinia nubilalis (European Corn Borer)
No common name, Exenterus amictorius. From Europe, to control Diprion similis (Introduced Pine Sawfly)
No common name, Lemophagus curtus. From the Palaearctic, 1969 and 1971, to control Oulema melanopus (Cereal Leaf Beetle)
No common name, Mesoleius tenthredinis. From the Palaearctic, to control Pristiphora erichsonii (Larch Sawfly)
No common name, Neotypus nobilitator. From the Palaearctic to control (?)
No common name, Olesicampe benefactor. From Europe, to control Pristiphora erichsonii (Larch Sawfly)
No common name, Phaeogenes nigridens. From the Palaearctic, to control Ostrinia nubilalis (European Corn Borer)
No common name, Phobocampe unicincta. From the Palaearctic, to control Lymantria dispar (gypsy moth)
No common name, Pimpla instigator. Probably from W Palaearctic, to control Lymantria dispar (gypsy moth)
No common name, Pimpla turionellae. From the Palaearctic, to control Cydia pomonella (Codling Moth)
No common name, Pleolophus basizonus. From the Palaearctic, to control Neodiprion sawflies
No common name, Temelucha interruptor. From the Palaearctic, to control Rhyacionia buoliana (European Pine Shoot Moth)


Remarks on stings
Despite conventional wisdom, there are ichneumonid wasps that are capable of stinging. While it is true that smaller species can't penetrate human skin with their ovipositors, larger species can. These stings are uncommon, however, and and occur due to direct, physical handling rather than from an instinct to protect young at a nest (as in the more familiar social wasps).

Incidents of stings typically involve the large, nocturnal ichneumonid species (i.e. Ophioninae & Netelia spp.). This capability is also known from larger members of Cryptinae, Phygadeuontinae, and Pimplinae with shorter ovipositors. Stings from long-tailed species such as Rhyssinae are virtually unheard of apart from ichneumonologists collecting specimens.

There has been debate as to whether ichneumonid wasps inject venom or not (i.e. dry sting). They do, with the likely exception of Xoridinae, possess a venom sac. Bob Carlson recounted an exceptionally rare incident where a Secret Service agent was stung by a species of Pimpla and developed a severe reaction (possibly due to allergy)(7), which would suggest venom to be involved.

Intensity has some variability as well. For instance, the genus Netelia has a more painful sting than the similar Ophioninae (esp. Ophion and Eremotylus).(8) Henry Townes also reported that some species of Cryptinae could be sore for several days, lasting longer than stings by most aculeate species.(9)
Works Cited
1.Classification and Systematics of the Ichneumonidae
2.Nomina Insecta Nearctica
Poole, Robert W. Nearctica.com, Inc.
3.Genera Ichneumonorum Nearcticae (2014)
4.Insects: Their Natural History And Diversity: With a Photographic Guide to Insects of Eastern North America
Stephen A. Marshall. 2006. Firefly Books Ltd.
5.Borror and DeLong's Introduction to the Study of Insects
Norman F. Johnson, Charles A. Triplehorn. 2004. Brooks Cole.
6.Hibernating Ichneumonidae of Ohio
Clement E. Dasch. 1971. Ohio J. Sci. 71: 270–283.
7.Unknown to Me
8.Catalog of Hymenoptera in America North of Mexico
Karl V. Krombein, Paul D. Hurd, Jr., David R. Smith, and B. D. Burks. 1979. Smithsonian Institution Press.
9.Is That A Stinger?