How to Get Rid of Mason Wasps and Their Nests

Mason wasps are solitary insects that build small mud nests in pre-existing cavities, and removing them is considerably simpler than dealing with social wasps like yellowjackets or hornets. Because mason wasps do not live in large colonies and rarely sting unless directly handled, you can often remove their nests with nothing more than a putty knife and some caulk. The more interesting question, though, is whether you should remove them at all, since these wasps are effective pest controllers in their own right.

Why You Might Want to Leave Them Alone

Before you reach for a can of spray, it is worth knowing what mason wasps actually do. Species like the red and black mason wasp (Pachodynerus erynnis) specialize in hunting caterpillars, including several agricultural and garden pests such as armyworms, cutworms, and loopers.¹ A female mason wasp captures and paralyzes caterpillars, then stuffs them into her nest cells as food for her developing larvae. A single nest can mean dozens of pest caterpillars removed from your garden over a few weeks.

Mason wasps are also genuinely docile around people. Unlike yellowjackets, which guard their colony entrance and will sting in swarms, a mason wasp has no colony to defend. She is a lone operator. If you walk past her nest or even stand next to it, she will generally ignore you. Stings happen almost exclusively when someone accidentally pinches or traps the wasp against their skin. If the nest is tucked into a wall crevice you rarely interact with, leaving it alone costs you nothing and benefits your yard.

That said, there are legitimate reasons to remove mason wasp nests. If they are nesting in weep holes your house needs for drainage, blocking ventilation openings, clogging outdoor electrical conduit, or if someone in the household has a severe allergy to hymenopteran venom, removal makes sense. The goal is to act deliberately rather than reflexively.

Recognizing a Mason Wasp Nest

Mason wasps do not build the papery, exposed combs you associate with paper wasps or the large enclosed nests of hornets. Instead, they look for a small existing hole and fill it with a series of cells made from mud, sometimes mixed with gravel or plant fibers. The visible sign is typically a small mud plug covering a hole in a wall, a piece of wood, a hollow plant stem, or even a gap in outdoor furniture. The plug is smooth or slightly rough, depending on the species, and is usually the diameter of a pencil or smaller.

Research on nest structure shows just how varied these sites can be. Some species nest in empty snail shells under stones, sealing a single cell with a plug made of glued gravel bits. Others colonize narrow holes in reed stems, packing as many as nine cells separated by partitions of gravel and mud into a single tube.² Around houses, the most common locations include old nail holes or screw holes in siding, gaps in mortar between bricks, holes drilled by wood-boring beetles, the ends of metal or PVC pipes, and wind chime tubes. If you see a small, neat mud cap covering any of these, you have found a mason wasp nest.

One detail that trips people up: mason wasps are sometimes confused with mud daubers, which are a different group of solitary wasps. Mud daubers build their own freestanding mud tubes or rounded mud nests attached to walls and ceilings. Mason wasps fill existing holes. If the mud structure is a tube or dome stuck onto a flat surface, that is a mud dauber. If it is a plug sealing an existing cavity, you are dealing with a mason wasp.

How to Remove a Mason Wasp Nest

Because there is no swarm to contend with, physical removal is the most effective and simplest approach. Here is how to do it safely.

• Time it right: The best time to remove a nest is in the evening or early morning, when the wasp is least active. If the nest has already been sealed and the adult wasp has moved on, timing matters less. A sealed mud plug with no wasp coming and going means the female has finished provisioning that cell and left.
• Scrape or pry the plug: Use a flathead screwdriver, putty knife, or similar tool to pop the mud plug out of the hole. The nest contents, typically paralyzed caterpillars and a wasp egg or larva, will be inside. Dispose of them if you do not want the nest to complete its cycle.
• Clean the cavity: Use a stiff brush, pipe cleaner, or compressed air to clear out any remaining mud partitions or debris inside the hole. Mason wasps sometimes reuse cavities that still contain old cell material, so thorough cleaning discourages re-nesting.
• Seal the hole: This is the critical step. Fill the cavity with caulk, steel wool, wood putty, or mortar depending on the material. If you scrape off the mud plug but leave the hole open, you are likely to see another wasp move in within days.

For nests in locations you cannot easily reach, such as deep inside a weep hole or behind siding, a long thin bottle brush followed by expanding foam sealant works well. Be cautious with expanding foam around weep holes, though, since those holes exist to let moisture escape from your walls. Replacing them with small mesh weep-hole covers is a better long-term solution that maintains drainage while excluding wasps.

Using Insecticide Sprays

Chemical control is rarely necessary for mason wasps, but if you have many nests in hard-to-reach spots or want to kill developing larvae inside sealed cells before removal, a residual insecticide dust like permethrin or carbaryl applied into the cavity with a hand duster will do the job. Dust formulations work better than liquid sprays here because the dust coats the inside of the tube and contacts any insect moving through it.

Aerosol wasp sprays designed for yellowjackets and hornets are overkill for mason wasps. They are formulated for knocking down aggressive social wasps at a distance, and that jet of pyrethroid aimed at a tiny hole in your mortar will mostly end up on your wall. If you do use one, spray directly into the hole rather than at the mud plug, wait a few minutes, then remove the plug and seal the opening.

A point worth making: insecticides do not prevent future nesting. They kill the current occupant, but the next mason wasp that comes along has no way of knowing the hole was treated unless residual dust remains inside. Sealing the cavity after treatment is what actually stops the cycle.

Essential Oil Repellents

If you would rather deter mason wasps from nesting in a particular area without killing them, essential oils are a partial solution. Research has shown that many plant-derived essential oils repel vespid wasps. In one study testing 21 oils against yellowjackets and paper wasps, 17 showed significant repellent effects, with clove, pennyroyal, lemongrass, ylang ylang, spearmint, and wintergreen among the most effective.³ A separate screening of 66 compounds found that certain monoterpenes and essential oils from the mint and daisy plant families also showed significant repellency against vespid wasps.⁴

There is an honest caveat here: these studies tested repellency on social wasps, not solitary mason wasps specifically. Mason wasps belong to the same family (Vespidae) but are in a different subfamily, so it is reasonable to expect some overlap in their chemical sensitivities, though the magnitude of effect could differ. In practice, people who apply peppermint oil or clove oil diluted in water around door frames, window sills, and known nesting holes report mixed but generally positive results. The oils evaporate within a day or two, so reapplication is necessary, which makes this more of a short-term deterrent than a set-and-forget solution.

A practical approach is to combine repellents with physical exclusion. Apply diluted essential oil around an area while you work on sealing nesting holes. The oil discourages wasps from the immediate vicinity long enough for the caulk to cure, and once the holes are sealed, the repellent becomes unnecessary.

Preventing Mason Wasps From Nesting

Because mason wasps are opportunists that exploit existing holes rather than excavating their own, prevention comes down to eliminating available nesting cavities. A thorough inspection of your home’s exterior in early spring, before nesting season begins, is the most effective single step you can take.

Focus on these areas:

• Mortar joints: Old or deteriorating mortar between bricks is a prime target. Repoint any joints with visible gaps or holes.
• Wood siding: Fill old nail holes, screw holes, and woodpecker damage with exterior-grade wood filler or caulk.
• Weep holes: Install stainless steel mesh weep-hole covers rather than plugging them. These allow airflow while keeping wasps out.
• Pipes and conduit: Cap open ends of unused pipes, conduit, fence posts, and hollow metal railings. Even a small piece of steel wool stuffed into the end works temporarily.
• Window frames: Gaps around old window frames, especially on the underside where caulk has cracked, attract nesting wasps.

You will never seal every possible cavity on a property, and that is fine. The goal is to exclude wasps from the spots where they are causing a problem or a nuisance. A mason wasp that nests in an old fence post at the back of the yard is doing you a favor. A mason wasp that nests in your front door frame is not.

When Mason Wasps Take Over Bee Hotels

If you have installed a bee hotel to attract native mason bees and other solitary pollinators, you have probably noticed that wasps love them too. Research on bee hotels found that native wasps were the most abundant group reared from these structures, comprising roughly 38% of all bees and wasps that emerged.⁵ Mason wasps, with their preference for pre-existing tubular cavities, are natural colonists of the same holes you drilled for bees.

Whether this is a problem depends on your goals. If you built the hotel specifically for pollinator conservation, wasp dominance can reduce the number of tubes available for bees. But the wasps using those tubes are beneficial predators eating pest insects, so the hotel is still serving an ecological purpose, just a different one than you intended.

If you want to tilt the balance toward bees, a few design changes help. Mason bees prefer tube diameters around 8 millimeters, while many mason wasp species favor slightly smaller openings in the 3 to 5 millimeter range. Offering tubes on the larger end of the bee-preferred range excludes some wasp species. Placing the hotel in full morning sun also tends to favor bees, which are more active in warm conditions, over some wasp species that tolerate shadier sites. Cleaning and replacing tubes each fall removes any overwintering wasp larvae and parasites, giving bees a fresh start in spring.

Natural Enemies of Mason Wasps

If you prefer to let nature handle the problem, mason wasps do have their own set of enemies. Various parasitoid wasps and flies specialize in attacking solitary wasp nests. The most commonly observed natural enemy is the cuckoo wasp, a brilliantly metallic green or blue wasp that sneaks into mason wasp nests to lay its own eggs. The cuckoo wasp larva then feeds on the mason wasp’s stored provisions or on the mason wasp larva itself. One study of the Australian mason wasp Abispa ephippium found that the parasitoid Stilbum cyanurum, a species of cuckoo wasp, was the only parasite detected at their nests.⁶

Other enemies include nest-usurping wasps from related species, various parasitic flies, and certain beetle larvae that invade sealed cells. Birds, particularly woodpeckers, sometimes peck open mud nests to eat the larvae inside. None of these natural controls are something you can deploy intentionally, but they are worth knowing about if you are seeing mason wasp populations fluctuate year to year on your property. A year with many cuckoo wasps can noticeably reduce the next generation of mason wasps without any intervention on your part.

Dealing With Mason Wasps in Walls and Masonry

The scenario that causes the most anxiety is when mason wasps are nesting inside your home’s walls, entering through gaps in mortar or siding. People sometimes worry these wasps will chew through drywall or cause structural damage. Mason wasps do not excavate. They cannot bore through solid materials. They use only holes that already exist, so the wasp is a symptom of a gap, not the cause of one. If a mason wasp got in, moisture, beetles, or settling cracks created the path first.

Occasionally, an adult wasp emerging from a nest cell inside a wall will wander inward instead of outward and end up inside the house. This is alarming but not dangerous. A single disoriented solitary wasp in your living room is easy to guide out with a cup and a piece of paper. If it happens more than once, it means there are multiple nest cells inside the wall cavity and you should seal the exterior entry point after the nesting season ends in fall, once all adults have emerged. Sealing during active season traps developing wasps inside, which can lead to more of them emerging indoors as they seek an exit.

For extensive nesting in masonry, a professional mason can repoint the mortar joints efficiently and address any underlying moisture issues that caused the mortar to deteriorate in the first place. This is a worthwhile investment because deteriorating mortar invites not just mason wasps but also mason bees, carpenter bees (which do excavate), and moisture intrusion that leads to much bigger problems than insects.

Wasp Traps and Why They Do Not Help Much Here

Commercial wasp traps baited with sugar water, fruit juice, or protein lures are designed for social wasps that forage in groups and communicate food sources to nestmates. Mason wasps are not attracted to these traps in any meaningful way. A solitary female mason wasp hunts specific prey, typically caterpillars, and returns directly to her nest. She is not cruising around looking for a sugary meal or a piece of your sandwich. Setting out a standard yellowjacket trap will catch yellowjackets, maybe a few flies, and zero mason wasps.

Fake wasp nests, the gray decoy bags sold at garden centers, are similarly useless. They are marketed on the idea that territorial social wasps will avoid an area where another colony appears to be established. Mason wasps are solitary and have no concept of colony territories. A paper decoy dangling from your eaves means nothing to them. Save your money and spend it on a tube of exterior caulk instead.