On this page
How to identify it
- Wasps about 1/2 inch to just over 1 inch long with a long, thread-like waist, often brightly or metallically colored.[1][3]
- The black and yellow mud dauber, also called the yellow-legged mud dauber, builds cells side by side or stacked into a rounded lump about the size of a lemon or a fist.[3][1][2]
- The common blue mud dauber is metallic blue. It doesn't carry mud; it brings water to old nests of other mud daubers and reworks them, leaving lumpy, irregular nests.[3][1]
- The organ pipe mud dauber is black with blue wings and white 'stockings' on the hind legs, and builds parallel vertical tubes that look like organ pipes.[3][1]
- Some mud daubers just plaster mud into existing cracks and round openings rather than building a separate nest.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Paper wasps and yellowjackets | Social wasps that build paper nests and defend them; mud daubers are solitary and build mud nests they don't defend.[2][3][1] |
| Spider wasps | Also narrow-waisted, often bluish black, and hunt spiders around eaves, but they have spinier legs with long hind legs that dangle in flight and are often seen dragging a spider on the ground.[3] |
| Mason and potter wasps | Some also build with mud, but they lack the long narrow waist and their nests look like little round pots or jugs.[3] |
Where it lives
The black and yellow mud dauber is native to North America and has been accidentally introduced to many other countries and islands. Nests turn up on building walls, eaves, barns, garages, bridges and in equipment openings; in nature they are built in cave entrances, under rock overhangs and in hollow trees.[6][3][1]
Biology and life cycle
Each nest is built and stocked by a single female; cells about an inch long are filled with paralyzed spiders, and one egg is laid per cell. Some species repair and reuse old nests.[1][3][2]
The female carries mud balls from the edge of a puddle; a cell takes about an hour to build, and she makes a buzzy 'singing' sound while applying mud.[3]
A black and yellow mud dauber nest may hold as many as 25 cells, each with about 10 spiders, though one cell can hold up to 40. This species prefers crab spiders and other small, colorful spiders.[3][1]
Individual females can specialize: in one population some took prey from only a single spider species, while others took spiders from up to 6 families.[7]
The sting paralyzes and preserves the prey. The larva feeds on the spiders and later chews its way out as an adult.[1][3]
In Missouri, mud daubers spend the winter as immature wasps in the nests, and the black and yellow mud dauber has two generations each summer. Adults drink nectar from flowers.[3]
Damage and signs
Health risk
Mud daubers don't defend their nests and rarely sting unless handled roughly or touched by accident; Clemson cites a pain rating of 1, the mildest on a 1 to 4 scale. Anyone allergic to wasp venom can still have a serious reaction.[1][3][2][4][5]
Control
Prevention
Caulk or plaster cracks where spiders hide, clear webs from corners, and screen or caulk openings into buildings so they can't nest there.[1]
Traps and physical control
Knock down or scrape off nests where they aren't wanted; removing nests may discourage mud daubers, and in winter they can be removed safely without spraying.[1][2]
Biological control
Consider leaving nests where you can tolerate them. Blue mud daubers stock their nests with black widow spiders and refurbish the old nests of the other species.[3]
If a mud dauber stings
Wash the sting with soap and water and apply ice wrapped in a clean cloth, 10 minutes on and 10 minutes off. An oral antihistamine may be used for mild symptoms.[4]
Have someone stay with the person to watch for an allergic reaction, and call 911 for trouble breathing or swelling of the face, mouth or throat.[5][4]
Where sources disagree
Whether spider hunting helps: Missouri's conservation department calls mud daubers beneficial because some hunt black widows; Clemson says the benefit is questionable because spiders also reduce insect numbers.[3][1]
Spraying nests: Clemson describes stream-type wasp sprays applied in early morning or late evening; UC IPM says nests can be removed in winter without spraying.[1][2]
Common questions
- Are mud daubers dangerous?
- Rarely. They're solitary, don't defend their nests and seldom sting unless handled.[1][3][2]
- Do mud daubers eat black widows?
- The common blue mud dauber stocks its nests with large numbers of black widow spiders, which its larvae eat.[3]
- Are old mud dauber nests safe to scrape off?
- Yes. UC IPM says nests can be removed safely in winter without spraying; in Missouri the young wasps spend the winter inside the cells.[2][3]
Sources
- Clemson Cooperative Extension Home & Garden Information Center, “Mud Daubers: Identification, Habits, and Control (HGIC 2512, revised 2025).” hgic.clemson.edu/factsheet/mud-daubers/ (accessed 2026-11-11)
- University of California Statewide IPM Program, “Pest Notes: Yellowjackets and Other Social Wasps, Publication 7450 (March 2012).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnyellowjackets.pdf (accessed 2026-11-11)
- Missouri Department of Conservation, “Mud Daubers (Field Guide).” mdc.mo.gov/discover-nature/field-guide/mud-daubers (accessed 2026-11-11)
- MedlinePlus, U.S. National Library of Medicine, “Bee, wasp, hornet, or yellow jacket sting (Medical Encyclopedia).” medlineplus.gov/ency/article/002847.htm (accessed 2026-11-11)
- Centers for Disease Control and Prevention, NIOSH, “Insects and Scorpions at Work.” www.cdc.gov/niosh/outdoor-workers/about/insects-and-scorpions.html (accessed 2026-11-11)
- Zootaxa, via PubMed, “The worldwide occurrence of Sceliphron caementarium (Drury, 1773) outside its native range, with new records (Ceccolini 2023).” pubmed.ncbi.nlm.nih.gov/37044485/ (accessed 2026-11-11)
- Behavioral Ecology, via PubMed, “Specialists and generalists coexist within a population of spider-hunting mud dauber wasps (Powell and Taylor 2017).” pubmed.ncbi.nlm.nih.gov/29622922/ (accessed 2026-11-11)
- iNaturalist, “Sceliphron caementarium taxon page (order and family).” www.inaturalist.org/taxa/121821 (accessed 2026-11-11)