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University of Minnesota Extension

Species guide - species detail

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Ephialtes decumbens (Ichneumonid parasitic wasp)


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Ephialtes decumbens is in the family Ichneumonidae. Ichneumonidae are parasitic wasps that use their long ovipositors to deposit eggs on, into, or near an insect host. It is a large family, with over 3300 described species in North America. The one nest in a Bee Atlas block that was parasitized by Ephialtes decumbens was in Hennepin County in 2017.


Ichneumonids are typically slender wasps with long ovipositors, sometimes up to twice as long as their body. They have long antennae with 16 or more antennal segments.

Nest Structure

Most Ichneumonids are parasitoids whose larvae feed and develop on a single host, although some species' larvae are mobile and will feed on more than one host. Hosts include a wide range of insects in the orders Hymenoptera, Lepidoptera, Diptera, Coleoptera, Neuroptera, and Mecoptera, and spiders and spider egg sacs. Most Ichneumonids are solitary. We only had one nest that was parasitized by Ephialtes decumbens in the Bee Atlas project. The nest host was a Trypoxylon wasp, a genus of wasps that prey on spiders.

Hole Sizes

No information at this time.


No information at this time.

Activity Period

No information at this time.


Triplehorn, C.A and N.F. Johnson. 2005. Borror and DeLong's introduction to the study of insects, 7th ed. Thomson, Brooks/Cole, Australia. Thank you to John Luhman for identifying all of our Ichneumonid specimens.

Minnesota Record Map

These data are from the Minnesota Bee Atlas project.

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