Ichneumon Wasp: All You Need to Know in a Quick and Easy Guide

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Ichneumon wasps are fascinating creatures belonging to one of the largest insect families, with over 4,000 species found across North America. These insects display a diverse range of forms, sizes, and colorations, making them an intriguing topic. While they share similarities with stinging wasps, ichneumons generally have a more slender build, longer antennae, and distinctive ovipositors in females.

The name “ichneumon” has Greek origins, meaning “tracker” and “footprint”, which is fitting considering the female wasps’ ability to hunt and track their prey. Ichneumon wasps are parasitic, meaning their larvae develop inside the bodies of other insects. This unique behavior makes them excellent natural pest control agents, as they help limit populations of potential pests.

Ichneumon wasps can be found in a wide variety of habitats and play a significant role in maintaining the balance of their ecosystems. Understanding the biology, behavior, and ecology of these insects provides valuable insights into the diverse world of invertebrates they inhabit. With thousands of species to study, the ichneumon wasp family holds countless opportunities for exploration and discovery.

Ichneumon Wasp Overview

Identification Features

Ichneumon wasps are a type of insect belonging to the family Ichneumonidae and order Hymenoptera. These slender wasps have several characteristic features that make them stand out:

  • Long, jointed legs
  • A narrow waist
  • Two pairs of wings
  • A long, slender abdomen
  • Long antennae

Size and Appearance

Ichneumon wasps have varying sizes, typically ranging from about 1/10″ to 1 1/2″ long. One species, Megarhyssa, can be nearly 3″ long including its very long tail-like ovipositor.

Colors and Patterns

These wasps exhibit a wide range of colors and patterns. Some have brightly colored bands on their abdomens, while others have more subtle markings. Many species have a sickle-shaped abdomen.

Family Ichneumonidae

Ichneumonidae is the largest family within the insects, with an estimated 60,000 to 100,000 species worldwide. The name “ichneumon” comes from Greek words meaning “tracker” and “footprint,” which relates to the hunting behavior of these parasitic wasps.

Order Hymenoptera

Order Hymenoptera consists of various types of insects, including bees, ants, sawflies, and wasps like the ichneumon wasp. They share some common features, like:

  • Two pairs of wings, with the front pair larger than the back pair
  • Abdomen connected to thorax by a narrow waist
  • Females typically possessing an ovipositor, used for laying eggs.

Comparison Table: Ichneumon Wasp vs. Other Hymenoptera Insects

Feature Ichneumon Wasp Bees Ants
Size 1/10″ – 3″ 1/8″ – 1 1/2″ 1/16″ – 1″
Legs Long, jointed legs Shorter, jointed legs Shorter, jointed legs
Waist Narrow, slender waist Broad waist Narrow, slender waist
Color Varied, can have bands Mostly black/yellow or brown Mostly brown, black or reddish
Behavior Parasitic, hunts for hosts Pollinators, social Social, display complex behaviors

Ichneumon wasp has many distinctive features and behaviors, placing it among the fascinating insects within the family Ichneumonidae and order Hymenoptera.

Life Cycle and Reproduction

Egg Laying and Hosts

Ichneumon wasps are known for their unique reproduction process. Female ichneumons use their ovipositor to inject eggs into a host’s body, typically a grub, caterpillar, or pupa1. Examples of host species include:

  • Wood-boring insects’ larvae
  • Larval pigeon tremex (a type of horntail wasp)2

Many Ichneumon wasps are specific to certain host species, ensuring they lay their eggs in particular environments suitable for their offspring’s survival.

Larvae Development

Once inside the host, ichneumon wasp larvae feed on the host’s body, eventually killing it. The development period varies depending on the wasp species and host type. Some important aspects of larvae development include:

  • Parasitism: Ichneumon wasp larvae are parasitic, depending on the host for nourishment and survival.
  • Environment: The host provides a suitable environment for the larvae to grow and transition into the pupa stage.
  • Host protection: Larvae might release chemicals to protect the host from other parasitic invasions, ensuring sufficient resources3.

Defining characteristics of ichneumon wasp larvae:

  • Feed on host’s body
  • Borrow sustenance from host

Pupa Stage

After fully consuming the host, ichneumon wasp larvae pupate, usually within the host’s body or inside a self-created cocoon. Key features of the pupa stage:

  • Transformation: The larvae transform into adult wasps
  • Duration: The duration in the pupa stage varies between species and environmental factors

Pros and cons:


  • Secured environment: The cocoon provides protection
  • Optimal conditions: Pupation occurs when conditions are suitable


  • Longer development: Transitioning to an adult may take time
  • Host-dependency: Relying on a specific host species makes them vulnerable to host population decline

Some ichneumon wasps emerge from the pupal stage as early as a few weeks, while others may take up to a year4. The adult wasps ultimately continue their life cycle by seeking new hosts and repeating the process.

Behavior and Interaction with Other Species

Parasitic Relationship with Hosts

Ichneumon wasps are known for their parasitic behavior with other insects, primarily targeting flies, beetles, moth and butterfly larvae as hosts for their eggs. They exhibit a remarkable ability to locate and inject their eggs into their hosts, typically within wood-boring insects or leaf-eating caterpillars. Some examples of host insects include:

  • Wood borers
  • Land invertebrates
  • Arthropods

Upon hatching, the wasp larvae feed on the host’s body, eventually causing its demise.

Predators and Preys

These wasps are considered beneficial insects as they play a vital role in controlling the population of various pests in gardens and forests. Although they are parasites to other insects, they themselves can become prey to larger predators such as birds and spiders. Ichneumon wasps also feed on nectar and pollen from flowers, making them important pollinators.

Interactions with Humans and Gardens

Most ichneumon wasps are harmless to humans, as their venomous sting is mainly used to paralyze their host. They can be an essential part of a garden’s ecosystem by providing natural pest control. Encouraging their presence can be done by planting diverse flower varieties to attract them with nectar and pollen.

Here is a comparison table of parasitic wasps and other insects:

Characteristic Ichneumon Wasps Other Insects
Biological Role Beneficial Parasite Varies
Prey Types Caterpillars, wood borers, etc. Varies
Ability to sting or harm humans Limited Varies

Overall, understanding the behavior and interactions of ichneumon wasps with their environment, hosts, and humans can help to appreciate their importance in maintaining balance within ecosystems and gardens.

Habitat and Distribution

North American Species

The Ichneumon Wasp is found in various habitats across North America. Some of the 4,000 species in this region live in places like Missouri. They coexist with different insects:

  • Ants
  • Bees

Comparison of Ichneumon Wasp with Ants and Bees:

Features Ichneumon Wasp Ants Bees
Body Structure Slender Segmented Plump
Antennae Length Long (16+ segments) Elbowed Short
Role Parasitic Social Pollination

Other Regions

This family of wasps is extensive, boasting around 60,000 worldwide species. As one of the largest animal species groups, they thrive in nearly all habitats.

Notable Ichneumon Wasp Species

Megarhyssa Macrurus

Megarhyssa Macrurus, also known as the giant ichneumon wasp, is a large species belonging to the family Ichneumonidae and order Hymenoptera. Some key features include:

  • Female stinger and long ovipositor used for laying eggs
  • Parasitizes horntails wood wasps
  • Does not pose a threat to humans

This species is particularly efficient in parasitizing horntails, as its long stinger allows it to penetrate wood and lay eggs in horntail larvae.

Trichogramma Wasp

Trichogramma wasps are tiny but effective predators of herbivorous insects, especially caterpillars. They can be used as a biological control method in agriculture. These wasps:

  • Lay eggs inside the eggs of other insects
  • Control pests, such as tomato hornworms
  • Are sensitive to temperature changes

Trichogramma wasps can be adversely affected by temperature fluctuations, which can impact their efficiency as predators.

Clothes Moths Parasites

Certain Ichneumon wasps act as parasites for clothes moths, which are notorious for damaging garments stored in closets. Key characteristics of these wasps include:

  • Tiny size
  • Specialized ovipositor for penetrating moth eggs
  • Reduction in moth populations

Their specialization has a positive impact on reducing the number of clothes moths, thereby preventing damage to garments.

Tomato Hornworms and Boll Weevils Predators

Ichneumon wasps prey on a variety of herbivorous insects, including tomato hornworms and boll weevils. These predatory wasps are helpful in controlling populations of these pests, which can cause significant damage to crops.

Here is a comparison table listing these species:

Wasp Species Target Pests
Megarhyssa Macrurus Horntails
Trichogramma Wasp Caterpillars, including tomato hornworms
Clothes Moths Wasps Clothes moths
Tomato Hornworms Wasps Tomato hornworms and boll weevils


  1. Life Cycle of Ichneumon Wasp

  2. Long-Tailed Giant Ichneumon Wasp

  3. Ichneumonoid Wasp Overview

  4. Ichneumon Wasp Species

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Ichneumon Wasp


strange but
Location:  Wisconsin
August 29, 2010 6:36 pm
I found this bug in my living room in Southeast Wisconsin. It looks like a winged ant but has a super skinny thorax and seems indestructable. I actually burned it before taking this photo and it still was partly alive.

Unknown Wasp

Hi Josh,
We do not recognize your wasp, but we hope one of our readers will be able to assist in its identification.  We wonder perhaps if it might be the little seen male of a species that exhibits sexual dimorphism, like possibly the American Pelecinid, which is only represented by females on BugGuide.  At any rate, burning this unknown wasp constitutes unnecessary carnage in our book.  Many times people kill benign or beneficial insects because they look fearsome or for other unfathomable reasons.

Eric Eaton provides an identification
Hi, Daniel:
No, that is an ichneumon wasp, possibly in the subfamily Pimplinae:
Not all Pimplinae have long ovipositors.  This specimen appears to have a short one, or else it is broken.

Letter 2 – Sabre Wasp from UK


Subject: Megarhyssa ?
Location: Petton, Shrewsbury, SY4 5TH
June 3, 2016 6:30 am
Hi, I live just outside Shrewsbury UK, this lovely chap just came into my house long enough for me to take a photo, is it a Megarhyssa and are they native to the UK. We do get quite a few Dragonflies around our pond and at first I thought it was one of them, obviously not – ant ideas?
Signature: Tom Brewin

Ichneumon: Rhyssa lineolata
Sabre Wasp

Dear Tom,
This Ichneumon is not in the genus
Megarhyssa, but rather, we believe it is related to Rhyssa lineolata, a species pictured on BugGuide.  We found Rhyssa persuasoria pictured on Nature Spot where it states:  “It searches for the larvae of Horntails or Longhorn Beetles which have buried in fallen timber. The female then uses her ovipositor to drill down to the larvae and then lay an egg which hatches and parasitize the poor host.” 

Thanks Daniel that’s very helpful, cheers … Tom


Letter 3 – Ichneumons from West Virginia


Subject: Flying insect
Location: Franklin, Wv
February 15, 2017 10:26 am
We live in a frame house with redwood siding. It is located in Franklin WV, in the mountains. The inset in the attached photo has shown up during the last two spring seasons. We typically see them between the screen and window in several rooms. It would seem that they must be coming out of the walls somehow, Once there was a swarm of perhaps 100 on the outside of the house under a kitchen window and just above the deck. While is is winter here with many sub-freezing days some of these insect appeared afrer a warm spell when it was 60-65F for a few days.
Signature: Pete Tuckerman


Dear Pete,
These are members of the order Hymenoptera, the insect group that contains Ants, Bees and Wasps, and our initial impression is that they are most likely Parasitoid Wasps that prey on other insects, possibly an Ichneumon or Brachonid, but we would not rule out that they might be grouped with the Symphyta that includes Sawflies, Horntails and Wood Wasps.  We will continue to research this, and we will contact Eric Eaton for his valuable input.

Eric Eaton provides Family identification.
Those are definitely ichneumon wasps.  May have nothing to do with any host living in the redwood siding.  Many species of ichneumons overwinter as adults, often in large numbers, so this is not an unusual phenomenon.  I suspect the wasps are hibernating in the walls, or nooks and crannies in the siding.  They don’t sting, so no worries there, either.
author, Kaufman Field Guide to Insects of North America

Letter 4 – Ichneumon Wasp


wood wasp?
August 20, 2009
Found at 8700′ elevation on the summit of Robinson Peak in Washington’s Pasayten Wilderness. Ichneumon? Wood Wasp?
Summit of Robinson Peak in N central WA

Braconid Wasp
Ichneumon Wasp

Hello again Tvashtar,
Your gorgeous images are monopolizing our postings today.  This is not a Wood Wasp.  It is a Braconid Wasp.  Braconid Wasps and Ichneumons are classified together in the superfamily Ichneumonoidea
of parasitic Hymenopterans.  We believe your specimen is in the genus Atanycolus, but according to BugGuide:  “Next to impossible to identify this genus from images alone, however it is one of the more common genera in the subfamily. Identification of images on this guide page are NOT absolute!”  It might also be in the subfamily Agathidinae, also represented on BugGuide.

Correction by Eric Eaton
August 29, 2009
… Thanks for the prompt.  I do have a couple other corrections:
The “braconid wasp” of August 20 is actually an ichneumon wasp, though I don’t know even which subfamily it belongs to.  Ichneumons are a real tough group even with specimens in hand….
… I’ll keep checking for other “errors,” but you are doing a bang-up job, Daniel.  Give my best to Lisa, keep in touch:-)

Letter 5 – Ovipositing Sabre Wasp from England


Subject: Please can you tell me what this is?
Location: Dalby forest. England
August 13, 2016 8:50 am
Saw this in the summer in north east England in a dense forest.
Signature: Perplexed

Sabre Wasp
Sabre Wasp

Dear Perplexed,
This is a parasitoid Ichneumon, the Sabre Wasp,
Rhyssa persuasoria, in the act of ovipositing, and you can verify our identification on Bio Images.  According to Bug Life:  “Wood drillers Ichneumons often locate their host species by ‘smelling’ them and this is exactly what Sabre Wasps do. Female Sabre Wasps locate the wood-boring larvae of the huge and beautiful Horntail Wasp (Uroceris gigas) by using their antennae to detect scents that emanate from the larvae’s wooden tunnels.  When a female Sabre Wasp has located a promising site, she starts tapping on the surface of the wood with her antennae. She then uses her long egg-laying tail to drill a ‘probe’ hole. She may drill a few probe holes before deciding on an appropriate position, and then drills as deep as she can. After 30-60 minutes, if successful, she will breach the tunnel wall, sting the larvae and then lay an egg on its body. With the larvae paralysed by the sting, it awaits the inevitable demise of being consumed alive by the Sabre Wasp grub.”  Your image is gorgeous, and though we have many similar looking images of North American relatives called Stump Stabbers in the act of ovipositing, your image is the first European example we have of your Sabre Wasp in the act of laying eggs.

Letter 6 – Parasitic Hymenopteran


Bug Id needed
Location: North Carolina, @ 15 miles west of I-95 and 10 miles south of Virginia border
November 19, 2011 5:36 pm
Hi Bugman,
We saw this beetle in the woods near Medoc, North Carolina (slightly south and west of Roanoke Rapids) sometime mid-November. It was on the underside of a fallen hickory-tree branch, I think. Please help me figure out what it is. Thank you!
Signature: Sanne King

Ichneumon, probably

Dear Sanne,
Your insect is not a beetle.  It is a Parasitic Hymenopteran, a group of wasps that parasitizes other insects and arthropods, usually by laying eggs that develop into internal parasites that kill the host insect, so they are important natural biological control agents.  We believe that this is most likely an Ichneumon (see BugGuide) or a Braconid (see BugGuide).  With few exceptions, this is a very difficult group to identify to the species level.

Greetings Daniel,
Thank you for your reply.  I am including a close-up of the little critter.  You’re right, and we weren’t sure it was a beetle, but it looked so solid at first.  The wings are quite opaque, and we didn’t notice any “wasp waist” or abdominal curvature.  It was keeping very flat on the leaf.  We’ve had no further luck in narrowing the species down.
Cheers, Sanne

There is no photo attached.

Letter 7 – Parasitoid Wasp from UK


Subject: what is this please
Location: cheshire, uk
October 12, 2012 2:56 am
my friend found this in work, it flew in through the window. could you please help identify it.
thank you
Signature: sharon

Parasitoid Wasp

Hi Sharon,
This is some species of Parasitoid Wasp, most likely an Ichneumon or possibly a Braconid.  We did not find any matching images in our initial web search.

Letter 8 – Two Wasps from Germany


Subject: Wasps, Sawflies? In Germany
Location: Hessen Germany
November 11, 2012 5:53 am
Love your site. It is what helped me figure out, a couple years ago, not to be so afraid of the House Centipede (which I’d never even heard of previously) who decided my bed was part of his/her daily path. We came to an understanding… I looked at pictures over and over on the net to get over my fear and s/he stopped visiting my bed after I tried to capture her (that was my ultimate goal in the attempt anyway; relocation).
Since then the site also helped me become even more interested in other insects, as I was already quite fascinated by spiders once I saw one eat her web she had strewn across a pathway I blundered into.
And so it is that I recently took pictures of what I think are some in the wasp/sawfly family in Germany, specifically the Hessen area in September/October.
The first one was moving so fast flying, landing, walking, repeat; apparently agitated at being stuck inside a tower but not knowing how to get out. There were several of these kind but I was in a bit of a hurry too with people, who don’t understand my interest in things so small, waiting for me.
The second was while on a walk. He (I believe) was on a rock with several ladybugs (which I will send a couple pics in of later though I believe they were all Asian — thank you for helping me identify those) on a path that was once an old Roman road (and apparently still goes to Warsaw, Poland). The path was surrounded by farm fields, some apparently organic while others seemed to be growing GMO corn and canola/rapeseed for biogas (there is so much of that in Germany). I think he may be of the xyelid family? I also have more pictures of this one.
The 3rd was already passed on, stuck in a spider’s web in town. I originally took the picture for the aesthetic reasons but after seeing the other two above and going through your wasp files I am now very curious about this one as well.
More to come soon of others (for some reason bugs in Germany have been finding me, nearly committing suicide even in the attempts :D).
Thank you for all you do (for us humans and the little ones we fail so often to understand)! 🙂
Signature: Curious Girl

Ichneumon Wasp

Dear Curious Girl,
Thanks for your wonderful letter.  We are not certain of the identity of your two wasps, but we are fairly confident that they are not Sawflies.  They both look like solitary hunters and Sawflies do not prey upon other arthropods.  We will continue to try to find out the species identities.  Your third photo doesn’t have much detail, but the creature caught in the spider web looks like a flying ant.

Unknown Wasp

Ed. Note:  November 16, 2013
These are most likely Ichneumon Wasps.


Letter 9 – Unknown Hymenopteran from United Kingdom is Ichneumon


Unknown Bug, Sorry
you hear it all the time, however, I’d just like to say what a fantastic library of data you have, really outstanding. I have searched the majority of your database, various other websites, and a book that I have, however, I cannot for the life of me find this creature. It looks like several things, but I’m not going to say what to make a fool of myself if they are way off the mark haha. Could you please help? This photo was taken in an area filled with overgrown plants, moist ground and no human interference. The creature is shown on the leaf of a gipsywort plant, a full sized plant specimen (or near full size).
Taken 10/09/2008 in Newport, South Wales, United Kingdom.
Dont mind ?


Dear Dont Mind,
We know this is the second time you have submitted this query, and we don’t know the answer. We haven’t the time to research at the moment, but we hope by posting your letter and photo, someone may write in with an answer. All we know for certain is that this is a Hymenopteran, the order that contains wasps and bees. We suspect it may be a wood wasp or sawfly, but we are not certain.

Karl provided us with a comment identifying this as an Ichneumon but he was unable to link to an image of Amblyteles armatorius. When we did a web search on the name he provided, we encountered this matching image.

Letter 10 – Ichneumon Pupa from Taiwan


Subject:  Butterflies or Moths
Geographic location of the bug:  Taiwan
Date: 05/11/2018
Time: 03:53 PM EDT
Your letter to the bugman:  Hi, I was wondering if you could help me identify this caterpillar.
How you want your letter signed:  Thanks! Libbi

Ichneumon Pupa

Hi again Libby,
We are greatly troubled as we are nearly certain we have identified a very similarly looking suspended pupa in the past, possibly from Australia, but we cannot recall what it is.  We are posting this as unidentified and we hope our readership will assist in the identification.

Update:  Ichneumon Pupa
Thanks to a comment from Cesar Crash, he directed us to this BugGuide posting of an Ichneumon pupa from the genus

Reader Emails


Letter 1 – Giant Ichneumon


Please………What’s this bug?
September 15, 2009
Please………What’s this bug?
• Your letter to the bugman    Found these at a day care. Is this bug something to be worried about?
cstan — MN
St. Paul, MN

Giant Ichneumon
Giant Ichneumon

Dear cstan,
This is a harmless female Giant Ichneumon in the genus Megarhyssa.  The long ovipositor cannot sting, and is used to lay eggs in wood infested by wood boring larvae of insects like the Pigeon Horntail.  The Pigeon Horntail larvae are the prey of the larvae of the Giant Ichneumon.

Letter 2 – Giant Ichneumon


wood boring bug
September 18, 2009
I observed this bug on this tree for over an hour. We live in Worcester County, MA
We also live near a small lake.
Boylston, MA

Giant Ichneumon
Giant Ichneumon

You have been mislead.  The Giant Ichneumon, Megarhyssa atrata, is not in the true sense of the word, a wood boring insect.  This non-stinging wasp relative is a parasitic Hymenopteran.  The female, like the individual in your photo, lays her eggs in trees that have been infested by Pigeon Horntail Larvae and other wood boring insects.  The larval Giant Ichneumon feeds on the wood boring insects.

Letter 3 – Giant Ichneumon


What the hell is this thing??
September 23, 2009
My uncle asked me to help him identify this insect. Picture taken today, Sept 23, 2009, in Hopkins MN. The tail end of this bug can fold out & fan out like a chinese fan and it looks like a left–bright green. The long probiscus’ off the back end of it were into the tree, not sure if it was eating something or putting eggs in or what.
Anne Rolli
Hopkins, MN

Giant Ichneumon
Giant Ichneumon

Hi Anne,
This is a Giant Ichneumon in the genus Megarhyssa.  She is depositing eggs under the bark and the larvae will feed on wood boring larvae.

Letter 4 – Giant Ichneumon


giant ichneumon survived windshield
June 2, 2010
This hit my windshield very lightly, and stayed for the rest of my ride home. Sorry the pictures are through my windshield, but there was NO WAY I was getting out of my car with that bad boy (or girl, actually) creeping around! You had other pics but this seemed more close up & I thought you might like them. Found in the Raleigh, NC area, end of April. Enjoy your site!
Creeped out but still fasinated
Raleigh NC

Giant Ichneumon

Dear Creeped out,
This is one interesting image of a Giant Ichneumon in the genus Megarhyssa.  We believe it is Megarhyssa macrurus, which is profiled on BugGuide.

I had my husband come out & flick it off my car before I’d get out, and I’m still thanking him for that! Glad you liked the pic well enough to post on your site (I’m somebody now lol), take care & keep up the good work.

Letter 5 – Giant Ichneumon


Dragonfly? Wasp? Hybrid?
June 8, 2010
I have lived in Vermont all my life but have never seen this before . Can you identify what this is?
Dave D.

Giant Ichneumon

Hi Dave,
This is a Giant Ichneumon in the genus Megarhyssa, and she is a female.  The long stingerlike ovipositor is used by the female to deposit her eggs deep inside wood that is infested with wood boring larvae of the Pigeon Horntail, the exclusive food for this parasitoid relative of wasps.

Giant Ichneumon

Letter 6 – Giant Ichneumon


Giant Ichneumon in New Jersey
Location:  Newton, New Jersey
July 20, 2010 6:50 pm
From a distance, I thought this was a dragonfly holding its wings in a funny position…then I saw the ovipositor, twice the length of the body. Is this a giant ichneumon, Megarhyssa nortoni? This is a first for me. It is resting on a grape leaf, near a rotting stump (perhaps after laying eggs?).
Northwestern New Jersey; photo taken July 20, 2010.

Giant Ichneumon

Hi Jeannie,
You are correct that this is a Giant Ichneumon in the genus
Megarhyssa, but we get a little murky at the species level.  We think that there is a very good possibility that your Giant Ichneumon is Megarhyssa nortoni, but we would also not discount Megarhyssa macrurus.  According to BugGuide, the range of Megarhyssa macrurus includes New Jersey, and the range of Megarhyssa nortoni includes nearby Massachusetts and Pennsylvania.

Giant Ichneumon

Your photos are all so great we have decided to post all three.

Giant Ichneumon

Letter 7 – Giant Ichneumon


Very Odd Looking Fly
Location:  East Moline, IL
August 11, 2010 11:19 pm
My co-worker had this insect come flying up to him in his office. He reluctantly captured it for me, and brought it to my office. I placed it in one of my special bug containers (I’m more inclined to find, research and keep spiders, but I like unusual bugs as well). I searched your site, but couldn’t find anything quite like it. Curious to see if you can figure out what it is. It was found on August 11, 2010, and our workplace is near the Mississippi River between IL and IA. It has what looks like an ovipositor that is nearly twice the length of its body.
Zee the Spider Guy

Giant Ichneumon

Hi Zee,
This parasitic hymenopteran is a Giant Ichneumon,
Megarhyssa macrurus.

Letter 8 – Bug of the Month September 2010: Giant Ichneumon


What IS this?
Location:  Southern Vermont
August 26, 2010 8:43 pm
This insect was on my porch in July. It died shortly after I saw and photographed it. Any idea what it is??

Giant Ichneumon

Hi KT,
We just posted another image of a different species of Giant Ichneumon in the genus
Megarhyssa, but your individual, Megarhyssa atrata, is the species most often reproduced in identification guides and entomology texts.  The black body with the accent markings of yellow face, antennae and legs make this an unforgettable insect, but the truly distinctive feature is the five inch long ovipositor of the female.  The female uses her ovipositor to deposit her eggs in the stumps of diseased trees that are infested with the wood boring larvae of the Pigeon Horntail, Tremex columba (see BugGuide), and we frequently receive images of female Giant Ichneumons drilling into stumps.  You may read more about Megarhyssa atrata in our own archive and on BugGuideBugGuide indicates on the genus page that the common name Stump Stabber is sometimes used.  In August 2007, we selected Giant Ichneumons in the genus Megarhyssa as our Bug of the Month, and we have decided that since three years have passes, we are clear to feature it again as the Bug of the Month for September with your letter and photographs.

Giant Ichneumon

Hi Daniel,
Wow, that’s awesome! Thank you both for the thorough response, and for choosing to feature my photos!
What a fascinating insect that is! It’s strange that I didn’t find any photos when I was surfing, but I probably wan’t entering adequate identifying words in the search. That was the first one I’ve ever seen, and I haven’t seen another since. Are they common in Vermont? They must be somewhat reclusive, as I have ‘hawk eyes’ when it comes to insects and spiders and the like. I am both fascinated by and enamored with them!
Thanks again! I’m heading to your site now!

Hi again KT,
They are not uncommon in Vermont, but like many insects, there may be a robust local population in an area, but seemingly identical conditions a mile away may have no individuals.

Addendum:  Giant Ichneumon Ovipositing
What kind of bug is this?

Giant Ichnuemon

What kind of bug is this?
Location:  Warwick, Rhode Island
August 29, 2010 4:17 pm
These bugs just showed up and crawl all over the dead tree on the side of my house the long antenna looking thing seems to maybe suck something out of the tree! I have never seen these before and they look like they could be 2inches long some shorter some longer! Its the end of August so we are slowly going into fall.
Thanks, Dawn Bergeron

Giant Ichnuemon ovipositing

Hi Dawn,
This insect is actually depositing eggs into the tree, not sucking something out as you thought. Several days ago we decided to make the Giant Ichneumon our Bug of the Month for September 2010 so we included information on how the female oviposits her eggs in the wood of dead and dying trees that contain the burrowing larvae of the Pigeon Horntail.  The Giant Ichneumon is a parasitoid whose larvae feed solely on the larvae of the Pigeon Horntail.  Coincidentally, yesterday we posted an image of a female Pigeon Horntail, another impressive non-stinging member of the order that includes wasps, in the act of oviposition.  Though we wrote a lengthy response, we were not able to include images of the actual egg laying or oviposition process.  Your photos clearly illustrate the process of a female Giant Ichneumon laying eggs, though your species is different from the species in the Bug of the Month posting, which is Megarhyssa atrata.  We suspect your Giant Ichneumon is Megarhyssa macrurus. We are going to combine your letter and images with the previously selected letter to be a joint Bug of the Month for September 2010

Giant Ichneumon Ovipositing


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

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  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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Tags: Ichneumon Wasps

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