Photo: xpda, CC BY-SA 4.0, via Wikimedia Commons
Kansas City Pest Identification
Chalybion californicumBlue Mud Dauber Identification
A metallic blue-black solitary wasp, closely related to the common mud dauber, that often reuses old mud dauber nests rather than building its own from scratch. Preys specifically on spiders, including black widows.
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How to Identify It
Iridescent metallic blue-black body with a narrow thread-like waist (less pronounced than the black-and-yellow mud dauber). Often seen entering or investigating old abandoned mud tube nests.
Size: 20–28 mm
Commonly Confused With
The common black-and-yellow mud dauber (different coloring, builds its own tubes rather than reusing others).
Why It Shows Up
Same sheltered, dry surfaces as other mud daubers — garages, eaves, porch ceilings — often reusing nests already present from prior seasons.
Where Homeowners Find It
Garage and shed walls, eaves, porch ceilings, and old mud dauber nest sites.
Seasonal Activity in KC
May through September.
Risk Level
Essentially none. They are not aggressive and rarely sting, and they actively reduce spider populations, including venomous species.
What You Can Do Yourself
- • Scrape off old nests if the mud staining bothers you; otherwise no action needed.
What Professional Treatment Involves
Covered under a general exterior wasp/nest service if requested, but rarely worth dedicated treatment on its own.
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Common Questions
How do I tell a blue mud dauber from something that looks similar?
The common black-and-yellow mud dauber (different coloring, builds its own tubes rather than reusing others).
Do I need professional treatment for blue mud dauber?
Covered under a general exterior wasp/nest service if requested, but rarely worth dedicated treatment on its own.