Four-toothed Mason Wasp

I grew up thinking that wasps were horrible, awful creatures who took great pleasure in stinging anyone who got near them. The proliferation of wasp-related memes on the Internet suggest that I wasn’t the only one who grew up with that belief and that many people still believe that. However, as I began paying more attention to all the different types of bees on my flowers, I also began to pay attention to the wasps. I noticed that not only were there more then just red wasps and black wasps, but they also weren’t trying to kill me. Slowly my trepidation turned to curiosity and I have started to learn a little bit about the different types of wasps that I encounter.

The four-toothed mason wasp (Monobia quadridens) is one of the wasps that I frequently find in the late summer and early fall. It is a black and white wasp with deep, iridescent, blue wings. Two similar looking wasps are the bald-faced hornet (Dolichovespula maculata) and one of the potter wasp species (Pseudodynerus quadrisectus). (Yes, the bald-faced hornet is technically a wasp, not a hornet.) All three are black and white wasps, but are relatively easy to tell apart if you pay attention.

The four-toothed mason wasp is a solitary wasp that collects caterpillars to feed to its young. It can often be found on flowers, especially in the late summer and early fall. Photo credit: Shannon Trimboli, all rights reserved.

The bald-faced hornet has extensive, distinctive white facial markings as well as white markings on the business end of its abdomen. Four-toothed mason wasps have white markings near the “shoulder areas” of the wings, a thin white band right behind the wings, and a single wide band at the front of the abdomen in the “waist area.” The rest of the abdomen is solid black, including the business end. Male four-toothed mason wasps often have a small white patch on their face, but it isn’t anywhere near as extensive as the bald-faced hornet’s facial markings. Female four-toothed mason wasps lack any white on their face. Pseudodynerus quadrisectus (it’s one of the potter wasp species, but doesn’t have its own common name) looks very similar to the four-toothed mason wasp, but has two white bands on its abdomen instead of one.

Four-toothed mason wasps are often found on flowers where they drink nectar as their primary food source. Some research has shown that they also ingest a decent amount of pollen. However, it is unknown whether they are actively consuming the pollen or accidentally swallowing it with the nectar.

Like many other types of wasp, the four-toothed mason wasp is a solitary wasp that feeds caterpillars to its young. Each female will search out an existing burrow or tunnel to use as her nest. These burrow or tunnels can include abandoned beetle tunnels, abandoned carpenter bee tunnels, hollow stems, and similar locations. The four-toothed mason wasp is one of the wasp species that will sometimes nest in bee hotels.

After finding a suitable nesting site, the female will begin searching for small caterpillars from several different families of moths. Several of the caterpillar species collected by the four-toothed mason wasp are considered economic and agricultural pests. The four-toothed mason wasp, therefore, serves as a free, beneficial, and natural source of pest control for these moths.

When she finds an appropriate caterpillar, the female four-toothed mason wasp will sting it, which paralyzes the caterpillar. She’ll then carry the caterpillar back to her nesting site. Once at her nesting site, she’ll place the caterpillar in the nest chamber, lay an egg, then build two walls out of mud with a small space between the two walls. She’ll then find another caterpillar and repeat the process.

Each nest chamber will contain multiple cells or rooms, each with its own egg and fresh caterpillar for the larva to eat when it emerges from its egg. Eggs that will produce female wasps are laid at the back of the chamber, while male eggs are laid at the front of the chamber. This is because the males take less time to develop and will emerge first. If they were laid at the back of the chamber, then they would kill all of their sisters as they chewed through the chambers in front of them to get out.

Over much of their range, four-toothed mason wasps have two generations each year. The first generation emerges in the spring to mate and lay eggs. The second generation emerges in the late summer. The eggs of this second generation will overwinter as larva in the nest chamber. In the more northern parts of their range, the four-toothed mason wasp may only have one generation each year.

Four-toothed mason wasps don’t go out of their way to sting you; I often get less than a foot away from them with zero aggressive response. However, they can sting if they feel overly threatened or are provoked. Their sting is often compared to that of a bald-faced hornet. One tidbit of information that I found interesting is that the males will defend themselves by jabbing the pointy end of their abdomen into whatever is bothering them. They lack a stinger so can’t really sting, but I’m sure it still doesn’t feel good.

Despite their ability to sting, I’ve found that four-toothed mason wasps are much like the bees that I enjoy observing. They are relatively calm and are much more likely to fly away than to come after me if I get too close. My likelihood of getting stung, therefore, is relatively low as long as I don’t do something stupid like try to grab one – which I have no intention of doing.

This article was part of Shannon’s original Kentucky Pollinators and Backyard Wildlife blog which evolved into the blog for Backyard Ecology.

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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