A Question of Palace Intrigue

The wasps seemed so nurturing.

Last month, I shared photos and videos of a paper wasp nest. I showed adults nourishing larvae until the little ones covered themselves with cozy silk blankies and snuggled in to pupate. So sweet…

Except, I left out the story’s cold-hearted, sinister part.

Take a look at this shady scene:
Why would a wasp haul a pupating larva from its cell and fill the empty cradle with a replacement egg? It’s the queen’s job to lay eggs. Had she offed her offspring?

Or had someone else done the dastardly deed? Looking for answers, I found an intriguing story. Here’s the headline:

Some paper wasp queens sit and wait to hijack or adopt another queen’s nest, Cornell researcher discovers.

The article explains that “…once a queen adopts a nest, she will eat the former queen’s eggs and young larvae and replace them with her own eggs.”

A-ha! A usurper queen! This was palace intrigue worthy of a Netflix drama.

Or was it?

The poor kid was dropped, not eaten. That could mean the clumsy queen poseur had simply lost her grip. But the victim was already pupating, not young as described in the Cornell research.

Still… I had filmed one adult taking an egg from a cell. And several times, I observed wasps divvy up, then feed a removed larva to its siblings. In this post’s header image, an adult is nibbling on what appears to be the leg of a removed pupa. Skullduggery! I continued my online search to learn about murder and mayhem among wasps.

One headline was particularly lurid.

Revolt in the Hive: Why Worker Wasps Sometimes Kill Their Queens

But I was watching larval removals, not regicide. Plus, I never saw one adult attack another, although it might have happened when I wasn’t filming. I kept reading.

This article held some explanatory promise:

Worker Wasps Sneak Out to Lay Their Eggs in Neighboring Nests

So, maybe intruders had snuck in, and the queen and her helpers were evicting the interlopers’ larvae and pupae.  That made me wonder: Can a queen tell if a larva or pupa hatched from another wasp’s egg? Sure enough, research suggests a wasp recognizes her eggs by smelling the sticky substance she produces to adhere the egg to its cell. That only works until the adhesive dries, however. I found no research suggesting a queen knows if a larva is her offspring.

It was behind less dramatic headlines that I ultimately learned reasons for the larval removal.

The first is waning food resources in late summer. With fewer caterpillars to feed the larvae, adults often reduce the number of hungry mouths. Fewer, but well-fed larvae increase the odds of rearing reproductive offspring. This behavior is part of a nest’s natural decline.

Adults will also remove sick or compromised larvae when viruses or parasites reach the nest. That’s well documented, although I’m still puzzled by some removals I saw. Sometimes, adults chewed holes in cell caps, reached in, and yanked out a developing pupa. How, I wondered, did they know the pupa—hidden behind that cap—had a problem? So far, I’ve not found the answer.

I also learned that paper wasp palace intrigue is indeed real. Female offspring of the foundress queen sometimes assert dominance and lay eggs. The queen is typically not amused and eats those eggs. The rogue daughters will often eat mom’s eggs, in return.

I should answer questions posed earlier in this post. Why would one queen hijack another’s nest? Why would workers kill their queen, or lay eggs in neighboring nests? I’m simplifying, but as best I understand, it’s all about reproductive strategy—seizing opportunities to insert one’s genes into the paper wasp pool. If you’d like the details, follow the links I inserted near the headlines above.

My curiosity about larval removal has been satisfied. But one mystery remains:

I see dead wasps, whole and partial, immobile in their pupal cells, as though frozen in mid-emergence. I noticed them early in my nest watch. The queen and her workers seemed to pay them no mind, as nest activity continued all around them.  Viruses and parasitoids are known to enter paper wasp nests, but none of what I read describes this outcome. I’m searching for possible explanations… stay tuned.

Resources

Wasp studies tend to focus on a single species. Everything I wrote is based on paper wasp research, but it’s possible that one behavior or another hasn’t been studied specifically with my neighbors, Polistes metricus, or metric paper wasps. That said, paper wasp articles, such as those published by university cooperative extensions, generalize as I have here.

Here’s a great paper wasp overview: Pugnacious Paper Wasps: Polistes Metricus or Maybe Polistes Parametricus, a Bug of the Week article by Michael J. Raupp, Ph.D. and professor of Entomology at the University of Maryland.

My favorite resource is an old one, a 100-page paper from the archives of The University of Michigan’s Museum of Zoology. Written in 1969, The Social Biology of Polistine Wasps by Mary Jane West Eberhard was a fascinating read. The author observed forty-seven wasp colonies for nearly 500 hours and documented some of the behavior I wrote about here.

A Fantastic Kids’ Book
Wasps are social insects, meaning they live in colonies that are organized societies with divisions of duties, including reproduction and care of their young. Here’s an award-winning book that follows the life of another social insect: Honeybee: The Busy Life of Apis Mellifera, by Candace Fleming, illustrated by Eric Rohmann. I love this book for its compelling (and accurate) storytelling, with backmatter about honeybee anatomy, bee research, and conservation at a time when bees’ survival is threatened. It’s a terrific read for kids and adults alike.

Image Credits: Carol Doeringer.