American Pelecinid Wasp: A Unique and Fascinating Critter

One day, late last summer, I decided to see how the berries were developing on the devil’s walking stick (Aralia spinosa) at the back of our property. The devil’s walking stick patch grows along the edge of the woods next to one of our fields. It was sunny, hot, and humid, so I decided to cut through the woods instead of walking through the fields. My plan was to avoid the pounding sun and hungry chiggers. I quickly discovered that the woods, although cooler than the fields, hosted an army of hungry mosquitoes. Oh well, I’ll take mosquito bites over chigger bites any day.

As I got close to the devil’s walking stick patch and began moving towards the edge of the woods, I caught a glimpse of something weakly flying near the ground. “Cranefly” immediately popped into my head. It was about the right size, but even though I only caught a glimpse out of the corner of my eye, something about it just didn’t seem right for a cranefly. I stopped and turned so that I could really see it. What I found was fascinating and something that I had never seen before.

The female American pelecinid wasp (Pelecinus polyturator) that I found. Photo credit: Shannon Trimboli, all rights reserved

Sitting on the vegetation was a skinny, but relatively large, black wasp with a “stinger” that was longer than the wasp’s body. I wasn’t worried though. I immediately realized that it had to be a parasitoid wasp of some sort and parasitoid wasps don’t bother people. My first guess was maybe some type of ichneumon wasp, but that’s my default guess for almost any wasp with a long stinger. I quickly took a few pictures before it fluttered off. My curiosity was peaked and I knew I had to try and figure out what I had seen as soon as I got back to the house.

I soon learned that what I had seen was a female American pelecinid wasp (Pelecinus polyturator). I was right about it being a parasitoid wasp, but wrong about it belonging to the ichneumon wasp family. American pelecinid wasps are the only species of its genus in North America. There are only 3 species in the entire genus (the other two are only found in Central and South America) and that Pelecinus is the only genus in its family. I quickly realized that I had stumbled upon a very unique and interesting animal.

Where to Look for American Pelecinid Wasps

There are two populations of American pelecinid wasps. One is found in North America, east of the Rocky Mountains. The other is found in Central and South America. There is a gap between the two populations so they don’t intermix. Members of our North American population are most often found in open deciduous woods with plenty of organic matter, near the edges of woods, and in gardens. They tend to stay relatively low to the ground. You may also sometimes find them on flowers because, like many other wasp species, the adults drink nectar.

What Do American Pelecinid Wasps Look Like?

The American pelecinid wasp is a skinny, glossy back wasp. The females have a long, curved, stinger-like tail. The stinger-like tail is jointed and is approximately 5 times the length of the rest of the wasp’s body. Once you know what to look for there really is no mistaking it. In reality though, the stinger-like tail, isn’t a stinger or a tail. Instead, it is her abdomen which has been highly modified for egg laying.

American pelecinid wasps completely lack a stinger, and therefore, have no way to sting anything. However, from what I read, that won’t stop it from jabbing its abdomen at you if you grab one. I can easily see how that would work as a pretty good bluff for potential predators.

Life History of the American Pelecinid Wasp

This is where things get really interesting. Remember those two distinct populations I mentioned earlier? Well, in the southern population, male American pelecinid wasps are common, and the wasps mate and reproduce like any other wasps. But that’s not true in the northern population.

Here in North America, male American pelecinid wasps are extremely rare. Almost all of our American pelecinid wasps are females. (The sexes are easy to distinguish because the males lack the elongated, jointed abdomen.) Since males are rare to nonexistent, most of our American pelecinid wasps reproduce through parthenogenesis. Parthenogenesis simply means that the eggs don’t have to be fertilized in order to develop into an embryo.

Females will slowly fly close to the ground or crawl on the ground with their abdomens curled behind them. When they are doing this, they are searching for June beetle grubs (Phyllophaga spp.) located under the ground. Scientists don’t know exactly how the females find the grubs, but somehow the females are able to detect the grubs.

Once the female detects a June beetle grub, she will insert her abdomen into the ground, sometimes almost 2 inches deep, and lay a single egg on the beetle grub. Again, how she knows exactly where the June beetle grub is underground, or even that it is a June beetle grub and not some other type of beetle grub, is still a mystery.

When the egg hatches, the wasp larva immediately chews through the beetle grub’s exoskeleton and begins eating the beetle grub alive. After consuming the grub, the American pelecinid larva pupates before eventually emerging as an adult. American pelecinid wasps typically start showing up in July with their numbers peaking each year in late summer or early fall (often August or September) before dropping off again as the seasons progress.

Scientists still know relatively little about the American pelecinid wasp, but what we do know makes this wasp a very unique and fascinating animal. As you are out and about this summer and fall, I encourage you to keep your eyes open for this amazing wasp. I’ve only ever found the one, but I’m hoping that I’ll find more now that I know what to look for.

Backyard Ecology: Exploring Nature in Your Backyard
Nature isn’t just “out there.” It’s all around us, including right outside our doors. Hi, my name is Shannon Trimboli, and I am the host of Backyard Ecology. I live in southcentral Kentucky and am a wildlife biologist, educator, author, beekeeper, and owner of a nursery specializing in plants for pollinators and wildlife conservation. I invite you to join me as we ignite our curiosity and natural wonder, explore our yards and communities, and improve our local pollinator and wildlife habitat. Learn more or subscribe to my email list at

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