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Why mud daubers are on spider patrol

UC Cooperative Extension advisors are on the front line and get the most interesting questions from our community. Someone brought some wasps into our office, and was worried they were invading her home, and wondered how to get rid of them. They were identified by the UC Davis Entomology Museum as black and yellow solitary mud dauber wasps, which are natural predators of spiders, and hence beneficial! Before you reach for that can of insecticide or heaven forbid, a blow torch to control spiders, talk to a UCCE advisor or Master Gardener in your county and read this blog for more information on managing them.

Yellow and black mud dauber wasps are predators of spiders but harmless to people. Adults are about 1-inch in length with true wasp waists!

Here's all you need to know about mud daubers and spider control

That mud you track into your house is nothing compared to what mud daubers can do — and what they do to spiders. Female mud daubers, or wasps, build mud nests for their young — and provision them with spiders.

Where are the nests and what do they look like?  

Female mud daubers, the architects, build those characteristic rectangular mud nests in protected areas of our homes, shops and garages, such as along eaves, walls or ceilings. Mud daubers are black and yellow solitary wasps (Sceliphron caementarium) that hunt spiders for their young. Another wasp, the blue mud wasp, reuses the black and yellow mud dauber wasp nests and primarily preys on black widow spiders.

Mud dauber wasp nests with holes where adults have exited after completing their immature stages.

Do mud daubers sting or bite? 

Mud daubers do not aggressively protect their nests. Unlike hornets and other social wasps, they are generally docile and rarely sting. 

Are mud daubers dangerous?

No, mud daubers are harmless and actually beneficial. They prey on spiders, including black widows, a favorite prey. They pack each cell with up to 25 to 30 spiders for their young. With about 15 to 20 cells per nest, that's over 500 spiders eaten. This is good news, especially for those of us who fear black widow spiders. True, mud daubers can be a nuisance, as their mud nests look messy, but they are generally peaceful.

How do they make their nests?

Females construct their nests by gathering globs of mud in their mandibles (jaws) from a nearby source of wet dirt. They carry the mud to a protected nest site, where they construct a cell. Then they begin hunting for spiders to provision the cell for their young, and lay a single egg inside. When they capture a spider, they sting it, permanently paralyzing it. This preserves the spider until their larvae are ready to eat it. When the cell is full of spiders, the female mud dauber caps it with more mud and builds another cell next to it. After the egg hatches and the food gone, she pupates. When an adult emerges, it opens the cap, leaving holes behind in the nest for the next cycle.

Mud daubers have a low reproductive rate, with about 15 to 20 eggs per female. Adults are active during the day during spring and summer with multiple generations per year. Queens overwinter in the cells in the larval stage. Adults sip nectar from flowers, where the male mud daubers are often found. Mud dauber wasps have good vision and use landmarks to locate nests and hunt spiders. They prefer protected areas where there are plenty of spiders. Sometimes you might see them going in and out of your house vents, hunting for spiders in your basement or attic.

Mud dauber pupa (right) and cells packed with spiders, showing the importance of these wasps for providing natural spider control.

How do mud daubers avoid being eaten by spiders?

Some are able to land on webs without getting entangled, and pluck the web to simulate an insect in distress. When the spider rushes to capture its prey, it becomes a victim of the wasp's paralyzing sting. The wasp then carries it back to her mud nest.

How do you get rid of mud dauber nests?

Although mud daubers are considered beneficial, you can remove the nests by scraping them off with a paint scraper or a knife into a dust pan, and then tossing them or moving them somewhere else where you don't mind their activity. The best time to remove the nests is in the late evenings when wasps are not active, or during the wintertime when they are dormant.

Do I have to worry about getting stung by a wasp or bit by a spider during nest removal?

No, the spiders are paralyzed and the wasps are not aggressive. Mud daubers can sting, but only if directly handled or if they accidentally snag in your clothing.

What's the best way to get rid of spiders?

Overall, spiders are beneficial because they're predators and feed on pests like flies. Most spiders cannot harm people. Those that might injure people — for example, black widows — generally spend most of their time hidden under furniture or boxes, or in woodpiles, corners or crevices. The spiders that we commonly see out in the open during the day are not aggressive toward people. The brown recluse spider has occasionally been brought into California in household furnishings, and other items, but it does not reside here. Spiders enter houses and other structures through cracks and are also carried inside on plants, firewood and boxes. 

According to the UC IPM Spider Management Guidelines, the best approach for controlling spiders in and around your home is to remove hiding spots for secretive spiders such as black widows, and regularly brush or vacuum webs from windows, corners of rooms, storage areas, basements and other seldom used areas. This is effective because their soft bodies generally cannot survive this process. If you see a dust-covered web indoors, it's no doubt an old web that a spider is no longer using.

Why should one protect mud dauber nests?

Because mud daubers eat spiders, especially the cryptic black widows. In the process of cleaning spiders and webs, be sure to try protect those mud nests, because mud daubers naturally help control spiders in and around your home.

Blue mud wasp adults favor black widow spiders. Photo credit: University of Florida Extension.
Posted on Tuesday, December 4, 2018 at 8:05 PM
Tags: IPM (2), Rachael Long (1), spiders (18)
Focus Area Tags: Pest Management

Why the Bohart Museum of Entomology Rocks!

Entomologist Joel Hernandez adds the finishing touches on a rock painted by his wife, Melissa Cruz, the outreach coordinator for the UC Davis Arboretum and Public Garden. (Photo by Kathy Keatley Garvey)

The Bohart Museum of Entomology at the University of California, Davis, rocks! Directed by Lynn Kimsey, UC Davis professor of entomology, the insect...

Entomologist Joel Hernandez adds the finishing touches on a rock painted by his wife, Melissa Cruz, the outreach coordinator for the UC Davis Arboretum and Public Garden. (Photo by Kathy Keatley Garvey)
Entomologist Joel Hernandez adds the finishing touches on a rock painted by his wife, Melissa Cruz, the outreach coordinator for the UC Davis Arboretum and Public Garden. (Photo by Kathy Keatley Garvey)

Entomologist Joel Hernandez adds the finishing touches on a rock painted by his wife, Melissa Cruz, the outreach coordinator for the UC Davis Arboretum and Public Garden. (Photo by Kathy Keatley Garvey)

What's a rock without a butterfly on it? (Photo by Kathy Keatley Garvey)
What's a rock without a butterfly on it? (Photo by Kathy Keatley Garvey)

What's a rock without a butterfly on it? (Photo by Kathy Keatley Garvey)

Isabelle Gilchrist, a second-year entomology major who staffed the family crafts activity table, displays a paint rock she created. (Photo by Kathy Keatley Garvey)
Isabelle Gilchrist, a second-year entomology major who staffed the family crafts activity table, displays a paint rock she created. (Photo by Kathy Keatley Garvey)

Isabelle Gilchrist, a second-year entomology major who staffed the family crafts activity table, displays a paint rock she created. (Photo by Kathy Keatley Garvey)

Members of Brownie Troop 3124 of Sacramento participated in the rock painting. In the foreground is leader Suzanne Enslow. The Brownies (from left) are Antonia Fedele-Mcleod, Adair Enslow,  and Amelia Pacheco, all seven years old. At right is activity leader Isabelle Gilchrist, a UC Davis entomology major. (Photo by Kathy Keatley Garvey)
Members of Brownie Troop 3124 of Sacramento participated in the rock painting. In the foreground is leader Suzanne Enslow. The Brownies (from left) are Antonia Fedele-Mcleod, Adair Enslow, and Amelia Pacheco, all seven years old. At right is activity leader Isabelle Gilchrist, a UC Davis entomology major. (Photo by Kathy Keatley Garvey)

Members of Brownie Troop 3124 of Sacramento participated in the rock painting. In the foreground is leader Suzanne Enslow. The Brownies (from left) are Antonia Fedele-Mcleod, Adair Enslow, and Amelia Pacheco, all seven years old. At right is activity leader Isabelle Gilchrist, a UC Davis entomology major. (Photo by Kathy Keatley Garvey)

The family craft activity at the Bohart Museum of Entomology
The family craft activity at the Bohart Museum of Entomology "rocked." (Photo by Kathy Keatley Garvey)

The family craft activity at the Bohart Museum of Entomology "rocked." (Photo by Kathy Keatley Garvey)

Sarah Luckenbill, 5 of Davis, created this colorful caterpillar. (Photo by Kathy Keatley Garvey)
Sarah Luckenbill, 5 of Davis, created this colorful caterpillar. (Photo by Kathy Keatley Garvey)

Sarah Luckenbill, 5 of Davis, created this colorful caterpillar. (Photo by Kathy Keatley Garvey)

Posted on Monday, September 24, 2018 at 5:17 PM

Everybody Loves Bugs, Right? Here Are the Top 25 Bug Blogs in the World

A flameskimmer dragonfly, Libellula saturata, perches on a bamboo stake in Vacaville, Calif. Native to western North America, it belongs to the family Libellulidae. (Photo by Kathy Keatley Garvey)

Everybody loves bugs, right? Well, no, they don't. Some folks scream, smash them, or sprint away from them. Other folks--including yours...

A flameskimmer dragonfly, Libellula saturata, perches on a bamboo stake in Vacaville, Calif. Native to western North America, it belongs to the family Libellulidae. (Photo by Kathy Keatley Garvey)
A flameskimmer dragonfly, Libellula saturata, perches on a bamboo stake in Vacaville, Calif. Native to western North America, it belongs to the family Libellulidae. (Photo by Kathy Keatley Garvey)

A flameskimmer dragonfly, Libellula saturata, perches on a bamboo stake in Vacaville, Calif. Native to western North America, it belongs to the family Libellulidae. (Photo by Kathy Keatley Garvey)

Close-up of the flameskimmer dragonfly, also called a
Close-up of the flameskimmer dragonfly, also called a "firecracker skimmer." (Photo by Kathy Keatley Garvey)

Close-up of the flameskimmer dragonfly, also called a "firecracker skimmer." (Photo by Kathy Keatley Garvey)

Flameskimmer in flight as he heads back to his perch, a bamboo stake. (Photo by Kathy Keatley Garvey)
Flameskimmer in flight as he heads back to his perch, a bamboo stake. (Photo by Kathy Keatley Garvey)

Flameskimmer in flight as he heads back to his perch, a bamboo stake. (Photo by Kathy Keatley Garvey)

Kids and Bugs Go Well Together: Check Out the Dixon May Fair

Dixon May Fair Youth Building superintendent Building superintendent Stephanie Hill (left) of Yuba City and assistant building superintendent Pat Connelly of Vacaville hang bumble bee pillow, the work of Solano County 4-H'ers. (Photo by Kathy Keatley Garvey)

Kids and bugs go well together. Take the entries in Today's Youth Building at the 143rd annual Dixon May Fair, which opened Thursday, May 10 and...

Dixon May Fair Youth Building superintendent Building superintendent Stephanie Hill (left) of Yuba City and assistant building superintendent Pat Connelly of Vacaville hang bumble bee pillow, the work of Solano County 4-H'ers. (Photo by Kathy Keatley Garvey)
Dixon May Fair Youth Building superintendent Building superintendent Stephanie Hill (left) of Yuba City and assistant building superintendent Pat Connelly of Vacaville hang bumble bee pillow, the work of Solano County 4-H'ers. (Photo by Kathy Keatley Garvey)

Dixon May Fair Youth Building superintendent Building superintendent Stephanie Hill (left) of Yuba City and assistant building superintendent Pat Connelly of Vacaville hang bumble bee pillow, the work of Solano County 4-H'ers. (Photo by Kathy Keatley Garvey)

Beekeeper Ryan Anenson, 16, of the Tremont 4-H Club, Dixon, took this blue-ribbon winner, close-up of a bee. Overlapping the photo are plant leaves. (Photo by Kathy Keatley Garvey)
Beekeeper Ryan Anenson, 16, of the Tremont 4-H Club, Dixon, took this blue-ribbon winner, close-up of a bee. Overlapping the photo are plant leaves. (Photo by Kathy Keatley Garvey)

Beekeeper Ryan Anenson, 16, of the Tremont 4-H Club, Dixon, took this blue-ribbon winner, close-up of a bee. Overlapping the photo are plant leaves. (Photo by Kathy Keatley Garvey)

Jake Vinum, 15, of Vacaville, won a blue ribbon for his wall hanging, titled
Jake Vinum, 15, of Vacaville, won a blue ribbon for his wall hanging, titled "Horseshoe Spider," cleverly crafted with a horseshoe and "spider legs." (Photo by Kathy Keatley Garvey)

Jake Vinum, 15, of Vacaville, won a blue ribbon for his wall hanging, titled "Horseshoe Spider," cleverly crafted with a horseshoe and "spider legs." (Photo by Kathy Keatley Garvey)

Khole Cahoon, 13, of Vacaville won a blue ribbon for her chocolate ganache cupcakes, decorated with bees. (Photo by Kathy Keatley Garvey)
Khole Cahoon, 13, of Vacaville won a blue ribbon for her chocolate ganache cupcakes, decorated with bees. (Photo by Kathy Keatley Garvey)

Khole Cahoon, 13, of Vacaville won a blue ribbon for her chocolate ganache cupcakes, decorated with bees. (Photo by Kathy Keatley Garvey)

Beekeeper Francis Agbayani, 12, of the Vaca Valley 4-H Club, Vacavile, is displaying his 4-H project,
Beekeeper Francis Agbayani, 12, of the Vaca Valley 4-H Club, Vacavile, is displaying his 4-H project, "Don't Bee Making Mistakes," a blue-ribbon winner. (Photo by Kathy Keatley Garvey)

Beekeeper Francis Agbayani, 12, of the Vaca Valley 4-H Club, Vacavile, is displaying his 4-H project, "Don't Bee Making Mistakes," a blue-ribbon winner. (Photo by Kathy Keatley Garvey)

Saving a Spider

A winter ant, Prenolepis imparis, encounters a Phidippus,  jumping spider in an almond tree on Bee Biology Road, UC Davis. (Photo by Kathy Keatley Garvey)

I did not save a spider yesterday. Did not save one today, either. Well, if I had seen one.... Wednesday, March 14 was "Save a Spider Day" in the...

A winter ant, Prenolepis imparis, encounters a Phidippus,  jumping spider in an almond tree on Bee Biology Road, UC Davis. (Photo by Kathy Keatley Garvey)
A winter ant, Prenolepis imparis, encounters a Phidippus, jumping spider in an almond tree on Bee Biology Road, UC Davis. (Photo by Kathy Keatley Garvey)

A winter ant, Prenolepis imparis, encounters a Phidippus, jumping spider in an almond tree on Bee Biology Road, UC Davis. (Photo by Kathy Keatley Garvey)

A blanketflower, Gaillardia, was a perfect meeting place for this crab spider and a bee,  Halictus tripartitus. (Photo by Kathy Keatley Garvey)
A blanketflower, Gaillardia, was a perfect meeting place for this crab spider and a bee, Halictus tripartitus. (Photo by Kathy Keatley Garvey)

A blanketflower, Gaillardia, was a perfect meeting place for this crab spider and a bee, Halictus tripartitus. (Photo by Kathy Keatley Garvey)

A crab spider dining on a  honey bee. (Photo by Kathy Keatley Garvey)
A crab spider dining on a honey bee. (Photo by Kathy Keatley Garvey)

A crab spider dining on a honey bee. (Photo by Kathy Keatley Garvey)

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