Are Ichneumon Wasps Dangerous? Uncovering the Truth

Ichneumon wasps are a large family of parasitic insects, comprising between 60,000 to 100,000 species worldwide.

They inhabit various locales and are commonly found in many habitats, playing a significant role in controlling garden pests.

While these wasps might appear intimidating due to their size, they rarely pose a threat to humans.

The primary purpose of ichneumon wasps is to hunt down other insects and lay their eggs inside the host.

When the ichneumon wasp offspring hatch, they feed on the host insect, eventually killing it. This makes them beneficial predators in your garden, as they control harmful pests.

Though ichneumon wasps do not possess stingers, some females have long ovipositors resembling stingers, which may intimidate observers.

However, these ovipositors only serve to lay eggs in their insect hosts, and they do not use them to attack humans. 

Overview of Ichneumon Wasps

Species

Ichneumon wasps, belonging to the family Ichneumonidae, are a diverse group of insects with over 25,000 identified species worldwide. Some common examples include:

• Netelia testaceus
• Ophion spp.
• Pimpla rufipes

Classification: Order Hymenoptera, Family Ichneumonidae

Ichneumon wasps are classified under the order Hymenoptera, which also includes ants, bees, and other wasps.

They are specifically part of the family Ichneumonidae, making them a type of parasitic wasp.

Characteristics of Ichneumon Wasps:

• Long, slender body
• Narrow waist, similar to other wasps
• Most species have a long ovipositor for laying eggs

Features unique to Ichneumonidae:

• Primarily parasitic on other arthropods
• Wide range of host species, including caterpillars and other insects
• Beneficial for controlling pest populations

Here’s a comparison table between Ichneumonidae and other Hymenoptera families:

Feature	Ichneumonidae	Other Hymenoptera Families
Parasitic Lifestyle	Yes	No
Beneficial for Pest Control	Yes	Depends on the family
Long Ovipositor (in most species)	Yes	No

Ichneumon wasps, despite being classified as parasitic, can be beneficial in controlling pests due to their predatory nature.

Physical Characteristics

Size

Ichneumon wasps vary in size, ranging from 3mm to 130mm in length. For instance:

• Pimpla species: around 12mm
• Megarhyssa species: up to 130mm

Antennae

The antennae of ichneumon wasps are distinctive features:

• Long and slender
• Composed of 16 to over 60 segments, depending on the species

Abdomen

The abdomen of these wasps is worth noting due to:

• Cylindrical or slightly flattened shape
• Long and slender in females, especially in egg-laying species

Coloration

Various colors can be observed in ichneumon wasps:

• Typically black or brown
• Sometimes with yellow, orange, or red markings
• Rarely metallic blue or green

Comparing a Pimpla species with a Megarhyssa species:

Feature	Pimpla Species	Megarhyssa Species
Size	Around 12mm	Up to 130mm
Antennae	Long and slender	Long and slender
Abdomen	Cylindrical	Long and slender
Coloration	Black or brown	Varied colors

Pros of ichneumon wasps:

• Effective biological control agents
• Help maintain a balanced ecosystem

Cons of ichneumon wasps:

• Can sting, but not harmful to humans
• May parasitize other beneficial insect species

Life Cycle and Reproduction

Eggs

Ichneumon wasps are parasitic insects known for their incredible reproduction process. Female ichneumon wasps possess long ovipositors that help them lay eggs on or inside their host insects such as caterpillars, flies, or beetle larvae.

Some examples of hosts include:

• Horntails
• Caterpillars
• Sawflies

Larvae

Once the ichneumon wasp eggs hatch, the larvae begin feeding on their host. This process is essential for the larvae’s growth and development. It ensures they consume enough nutrients to transform into pupae.

Pupa

After a period of feeding, the ichneumon wasp larvae will form a protective cocoon and enter the pupal stage.

Ichneumon wasp cocoons can be found in various environments, including soil, plant stems, and host insects’ remains. Inside the cocoon, the larva prepares its transition into an adult wasp.

Adults

Upon completion of the pupal stage, adult ichneumon wasps emerge from their cocoons, ready to start the reproduction cycle anew.

Comparison Table:

Life Stage	Key Features
Eggs	Laid on or inside host insects
Larvae	Feed on host insects for growth
Pupa	Formed inside a protective cocoon
Adults	Emerge ready to reproduce

Though ichneumon wasps are parasitic, they do not pose a threat to humans. These wasps are beneficial in controlling the population of pest insects and maintaining a healthy ecosystem balance.

Are Ichneumon Wasps Dangerous?

Sting

Ichneumon wasps are not considered dangerous to humans. Their sting is mainly used for:

• Paralyzing prey
• Laying eggs inside host insects

However, they can sting if mishandled or threatened, but the sting is rarely painful.

Ovipositor

The ovipositor is a unique feature of female ichneumon wasps. It is:

• Long and needle-like in appearance
• Used for laying eggs inside host insects

For example, Megarhyssa can drill 1/2 inch or more into the wood with its ovipositor to deliver an egg into the horntail larva.

Venom

Ichneumon wasps do not produce venom harmful to humans. Their venom is specialized for paralyzing prey, enabling the wasp to lay its eggs.

Interactions with Humans

Generally, ichneumon wasps are considered beneficial due to their role in controlling pest populations. They are not aggressive towards humans and will usually ignore people.

The following table compares ichneumon wasps and other common wasps to highlight key differences.

	Ichneumon Wasps	Common Wasps
Sting	Rarely painful	Painful and intense
Venom	Not harmful to humans	Potentially harmful to humans
Aggression	Low	High (when threatened)
Benefits	Controls pest populations	Pollination, pest control

Ecological Role of Ichneumon Wasps

Parasitic Relationships

Ichneumon wasps, members of the Ichneumonidae family, are known for their parasitic relationships with various host insects. They have diverse lifestyles, and many are parasitoids.

They lay their eggs inside or on other insects like caterpillars, grubs, and spiders. After hatching, the larvae feed on the host, eventually causing its death.

• Host species: Caterpillars, grubs, spiders
• Result: The host is killed once the wasp larvae finish feeding

Predation

Although the adult ichneumon wasps do not directly prey on other insects, their larvae feed on the host insects. There are some cases where the larvae may even pupate within their host organism, further impacting the host species’ population.

• Predation style: Indirect predation via larvae
• Effects on host populations: Reduction in host insect numbers

Beneficial Impact on Pest Control

Ichneumon wasps play a positive role in pest control within ecosystems, as their parasitic lifecycle often targets pest species like moths and tomato hornworms.

The parasitic wasp, Megarhyssa, found on declining or dead hardwood trees, specifically targets horntail wood borers, a type of insect that causes damage to trees.

• Pest species targeted: Moths, tomato hornworms, horntail wood borers
• Impact: Natural and biological pest control in various habitats

Ichneumon Wasps	Megarhyssa
Focus on pests like moths and tomato hornworms	Targets horntail wood borers
Found in various habitats	Found on declining or dead hardwood trees

Ichneumon wasps are not known to be aggressive, and they ignore humans when possible. They have, however, been documented using their ovipositors to protect themselves if mishandled.

• Aggression towards humans: Low
• Self-defense: Ovipositor may be used if mishandled

Notable Ichneumon Wasp Species

Megarhyssa

The Megarhyssa is a large ichneumon wasp species, known for its impressive size and long ovipositor. Its characteristics include:

• Length: 1.5 to 3 inches
• Ovipositor: can be longer than the entire body

These wasps use their ovipositor to lay eggs inside wood-boring insects, providing a valuable ecological service.

Giant Ichneumon Wasp

The Giant Ichneumon Wasp is a fascinating species with distinctive features:

• Size: similar to Megarhyssa
• Antennae: long and whip-like
• Abdomen: longer than head and thorax combined

While they might appear intimidating, they pose no threat to humans as they do not sting.

Hybrizontinae

The Hybrizontinae subfamily is less well-known but still unique. Some features of this group include:

• Host: typically targets beetle larvae
• Distribution: found mainly in dry forest habitats

As with other ichneumon wasps, the Hybrizontinae species are harmless to humans.

Species	Size	Features	Sting
Megarhyssa	1.5 to 3 inches	Long ovipositor	Doesn’t sting
Giant Ichneumon	Similar to Megarhyssa	Long antennae, elongated abdomen	Doesn’t sting
Hybrizontinae	Varies	Targets beetle larvae	Harmless to humans

These notable ichneumon wasp species play essential roles in controlling pests and thus contribute to a balanced ecosystem. Despite their sometimes intimidating looks, these insects are not dangerous to humans.

Conclusion

Ichneumon wasps are known for their ability to down pests and lay their eggs inside the host.

Yes, their appearance might be a little intimidating particularly because of their size, but they do not pose a threat to humans.

These insects avoid human interaction and focus on laying eggs inside their hosts. When the larvae hatch, they start consuming the host insect and end up killing it.

Their incredible ability to eliminate pests makes them beneficial predators in gardens. Despite having no stingers and being non-venomous, these insects may appear scary.

Some females have long ovipositors resembling stingers, which may intimidate observers. Thankfully, these ovipositors are not used to attack; They are used to lay inside the host bodies.

Understanding their behavior can help us preserve these insects and enjoy the benefits of natural pest control.

Reader Emails

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

Letter 1 – Flightless Ichneumon, we presume

What’s This Bug?
Location: Chicago land
March 4, 2011 12:37 am
I found this ant-like insect on my basement workbench, I thought it was a regular old ant, but I noticed the stinger on its back.

 I’m in the Chicago land area and the outside temperatures got above freezing this day (3-2-11) it’s really small about 1/8 of an inch (I used a 60mm macro lens with an extension tube)
Thanks
Signature: Bill G

Hi Bill,
We can only surmise that this is some species of flightless Parasitic Wasp.  We need to rush off and cannot research this at the moment, though we have requested assistance from Eric Eaton. 

Moments before posting, we decided to try to locate any Flightless Ichneumons, and BugGuide has numerous images in the genus Gelis.  BugGuide states:  “Many species of Gelis are wingless. Habits are diverse.

Many are external parasites of Lepidoptera in cocoons, others are parasitic on Symphyta, spiders, Diptera larvae and pupae, or wood-boring Coleoptera larvae. Many are Hyperparasites.”

Eric Eaton provides confirmation
Daniel:
Wow! Great image of an adult female ichneumon wasp in the genus Gelis:
http://bugguide.net/node/view/41499
May I use this image in one of my blogs I wonder? 🙂
Eric

sure he can use it, no problem, and thanks for the info, BTW is this bug a common thing or something that I should be concerned about? since I found another one by my back door?
also, great website you have, it’s now bookmarked
Thanks
Bill Grenchik

Hi Bill,
We are copying Eric Eaton with your response.  There is no need to be concerned regarding the Ichneumon.  We understand that some Ichneumons are capable of stinging, but that is a rare occurrence if they are carelessly handled.

Letter 2 – Flightless Female Parasitoid Wasp

Subject: Longhorn Ant?
Location: Southern New Jersey
January 11, 2013 2:19 am
Ok, this one has me stumped. I spotted this inside the house on Nov. 25 and I cannot remember seeing anything similar to it before. I’m not even sure whether to call it an ant, ground wasp, or other. The insect is about 1/2 inch long and walked in an ant-like fashion.
Signature: Wileyscott

Dear Wileyscott,
We deduced because of the stinger and the antennae that this was a female Parasitoid Wasp, most likely an Ichneumon, and we were correct.  Upon researching, we matched your image to this photo of a Gelis species female on BugGuide. 

BugGuide notes that there are over 82 species in the genus in North America, and in our opinion, they look very much alike.  BugGuide also notes:  “Many species of Gelis are wingless. Habits are diverse.

Many are external parasites of Lepidoptera in cocoons, others are parasitic on Symphyta, spiders, Diptera larvae and pupae, or wood-boring Coleoptera larvae. Many are Hyperparasites.”  Ichneumons, Wasps, and Ants are all in the same Order, Hymenoptera.

Thank you! I am familiar with Ichneumon at least by name, but I was unaware there were wingless varieties.
Scott

Letter 3 – Ichenumon

Subject: What is this bug?
Location: Memphis, TN
December 12, 2015, 6:03 pm
Hello,
I found this guy crawling on me. I live in Memphis, TN. It was on me yesterday (December 11, 2015).

The weather is unusually warm here right now. It looks like some sort of wasp-like bug, but I have never seen one with this coloring.
Thanks,
Signature: Vera

Dear Vera,
This is a parasitic relative of wasps from the family Ichneumonidae, and based on the black and white antennae, we believe it may be in the genus Cryptanura which can be found on BugGuide. 

Ichenumons are considered harmless to humans as most members of the family do not sting. 

In our effort to educate the public about insects, we have created an Unnecessary Carnage tag and we hope any future encounters you have with this harmless beneficial insect will not result in a similar outcome.

Thank you, Daniel! Hopefully, the next time I encounter one, it won’t be in my shirt. ?

Letter 4 – Ichneumon Pupa from South Africa

Subject:  Chrysalis perhaps ??
The geographic location of the bug:  Cape Town South Africa
Date: 09/13/2018
Time: 06:46 PM EDT
Your letter to the bugman:  Hi there I found this on our house keeper.  I have never seen this before and wonder if you could please identify it, please. Thank you sincerely. Cheryl
How you want your letter signed:  Cheryl Combes

Dear Cheryl,
We are quite certain we have a similar-looking hanging pupa in our archives, but we cannot remember its identity this morning. 

We are currently very pressed for time, so we are posting your image as unidentified and we hope one of our readers will be able to provide a comment with its identity.

Update:  September 17, 2018:  Thanks to comments from both Cesar Crash and Karl, we are now able to link to another Ichneumon pupa in our archives.

Reader Emails

3847

Letter 1 – Google led her to What's That Bug?

 

Giant Ichneumon
Dear Bugman,
I googled long tail flying bug and came across your website. (totally awesome by the way!) My husband spotted this bug on our driveway the other day and couldn’t believe his eyes. After looking at it I was totally surprised, I had never seen a bug so big! At first we thought the tail was a stinger. OUCH!! After seeing the photos on your website we agreed it must have been a female giant ichneumon wasp. Are these insects found all over the U.S.??
Jane
in NH

Hi Jane,
Thanks for the compliment. Giant Ichneumons in the genus Megarhyssa are found in the North, South, East and West, but different species are found in different locales.

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 – Ichnuemons

 

Ichneumom in Wisconsin
Thank God I found you!!!!
After what seemed like hours of trying to identify this lovely bug I found what I was looking for on your lovely web site. You have now been added to my "favorites" list. What a great site can’t wait to share it with my kids. Anyhow these interesting bugs are primarily active in July and August…yes? And the adult insect emerges from the wood after devouring it’s host…yes? And they are not harmful to humans…right? do they ever host off of other wasps or bees? I have never seen one of these before are they common to Wisconsin? If not where might it have come from? Just curious…well alright very curious after all I have just spent the past two hours trying to identify this creature and it is now 1:46 in the a.m. Peace,
Jill

Hi Jill,
Thanks for the nice letter. Ichneumons prey on wood boring larvae, usually beetles but possibly also horntails, wasp relatives. Perhaps the sudden population explosion of Ichneumons has something to do with the Asian Longhorn Borer infestation that is occurring, especially in Ash forests.