Mud Dauber

Sceliphron caementarium

Mud Dauber

Sceliphron caementarium

Harmless

Not dangerous

Harmless. Solitary, no colony to defend, and among the least defensive wasps you will meet. It stocks its nest with paralysed spiders and has no interest in anything larger.

Size24–28 mm

MarkingsExtremely long thread-like waist, longer than on any wasp people usually see · Black with yellow legs and yellow marks on the thorax

WhereSheltered vertical surfaces — porch ceilings, garage walls, sheds, under eaves and bridges. Anywhere dry and out of the rain.

SeasonAdults through summer

How to tell it apart

Extremely long thread-like waist, longer than on any wasp people usually see
Black with yellow legs and yellow marks on the thorax
Nest is a smooth mud tube or a cluster of tubes on a sheltered wall
25–28 mm, slender rather than heavy
Seen collecting mud at puddle edges and damp ground

Where you’ll find it

Across the whole United States.

Sheltered vertical surfaces — porch ceilings, garage walls, sheds, under eaves and bridges. Anywhere dry and out of the rain.

Adults through summer.

How it behaves

The female builds the nest alone from mud collected at puddles, packs each cell with spiders she has paralysed — often several dozen per cell — lays an egg and seals it. She then leaves. There is no colony, no guard and nothing behind her worth defending, which is why mud daubers can be worked around at close range without incident. They are a significant predator of spiders, including black widows.

You’ve found one indoors

You can leave it or scrape it off, and neither decision is risky. Old nests with round exit holes are empty and can be knocked away with a scraper. If you would rather they did not build there, the effective measure is removing nests early each season, since a good sheltered wall gets reused year after year.

Common questions

Do mud daubers sting?

They can, and essentially do not. They are solitary and have no nest defence instinct. Handling one is about the only way to be stung.

What is inside the mud tubes?

Paralysed spiders and a wasp larva. Each cell is stocked with spiders the female has stung, sealed, and left for a single offspring to eat.

Is it safe to knock the nest down?

Yes. If the tubes have neat round exit holes they are already empty. Even an active nest carries very little risk, because the female does not defend it.

Do they come back to the same place?

Reliably, if the spot is dry and sheltered. A porch ceiling that had nests last year will get them again, which is why removing them early works better than removing them late.

Commonly confused with

Great Black Wasp Harmless
Cicada Killer Harmless

Keep identifying

Identify another animal from a photo or return to the Ants & wasps guide.

Previous: Cicada Killer · Next: Velvet Ant

Where this was checked

iNaturalist — Sceliphron caementarium checked 2026-07-30

Last reviewed 2026-07-30. We identify, we don’t diagnose — what we can and can’t tell you.