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Posts Tagged: IPM

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 (40), Rachael Long (35), spiders (19)
Focus Area Tags: Pest Management



JOB ANNOUNCEMENT The UC Statewide IPM Program, which is a part of the Division of Agriculture and Natural Resources, is hiring for an Urban IPM Educator. This position is part of the Urban and Community IPM unit. Under the direction of the Associate Director for Urban & Community IPM, the...


Posted on Tuesday, October 30, 2018 at 9:18 AM
Tags: announcement (227), IPM (40), Job Posting (6)

Gopher Management in School and Community Gardens

Pocket Gopher: Ag Natural Photography by Ed Williams
Pocket gophers, more commonly known as gophers, are one of the most common vertebrate pests found in school and community gardens. They are known for their extensive burrow system through the soil and also for the damage that they can cause to plants in gardens. Gophers are also known to chew on irrigation systems. They are responsible for soil erosion since they move soil to the surface when they construct their burrow systems. Their tunneling can damage turf and the mounds they leave behind can be tripping hazards.

Pocket gophers are rarely seen above ground but sometimes you can see them popping out of a feeding hole. They are small mammals with small eyes and ears and have fur lined cheek pouches (pockets) for storing food.

Pocket gophers are considered nongame wildlife, which means that they can be managed by any legal means. In school and community gardens there are many options.


Trapping is one of the easiest ways to curtail a gopher issue in a school or community garden. It is really important to monitor the issue and insure that the problem does not get out of hand since gophers are very prolific breeders and are easier to manage when there are less of them.

There are many trap options for trapping gophers. It is important to consider public safety when using these tools. Traps are often very tightly sprung and could damage fingers and toes of anybody that unexpectedly steps in a set trap. While research has shown that it is not necessary to cover over your trap sets and close them up, it is important to reduce the risk of exposure to a trap, especially in a school setting. It is recommended that trap sets in this scenario should be covered and inaccessible to youth.

Gopher burrow entrance

There are some toxicants that are available to unlicensed professionals for use on gophers. The most commonly available products are those containing zinc phosphide. These products are applied below the ground and therefore risk of exposure is very low. Bait shyness can be associated with this active ingredient so it is important to monitor the issue and ensure that it is being reduced. Otherwise, you may be applying rodenticide that is not being consumed.




Fumigation is a common and often successful way to manage gophers. However, many of these products are considered Restricted Use Pesticides and can only be applied by a licensed professional. Products like gas or smoke cartridges are not considered effective for the management of gophers.


Gophers can be excluded from school and community gardens but the costs of installing underground fencing can be cost prohibitive. Instead, consider excluding gophers from smaller areas like raised beds. Remember that gophers can travel above ground too, so if you install wire fencing with a ¾ inch mesh, be sure to extend it above the ground also. Wire baskets can also be used to exclude gophers from the root systems of high value trees and shrubs. You must take care to ensure that these baskets do not restrict the growth of the roots.

For more information on gophers and other vertebrate pest, please visit the UC IPM Pest Notes.

Rat Management in School and Community Gardens.

It is important for food-safety reasons to manage rats in school and community gardens. Rats and other wildlife can carry a number of diseases that can be deposited in the form of urine and feces on fruit, vegetables, and in the soil. Rats can also directly damage fruit and vegetables by consuming the produce entirely or by gnawing on parts of it and making it unfit for human consumption. Norway rats create burrows that can compromise beds and root systems. While rats can also chew on drip irrigation and damage the tubes, it is more common for some other wildlife species to chew on these.

Managing rodents in and around school and community gardens can be difficult. One of the easiest ways to keep many rodents at bay is to remove their food source. Given that the main purpose of a garden is to grow food, it would be counter-intuitive to remove the food. However, there are many management options available to people working in gardens that are trying to protect their food from rat damage. 

Habitat modification and sanitation

Making sure that the landscape surrounding your garden is well maintained may help with the management of rats.  Lots of cover in the form of landscaped shrubs, trees, untrimmed palm trees etc. can provide a lot of harborage for rats to live in. These should be trimmed up and off the ground and should not be densely planted if they are in the area. Compost can provide ample harborage for rats.  It is recommended to not compost food in the immediate vicinity of your garden and any other green waste should be attended to regularly to make sure that rats do not establish colonies in compost piles. Feeding of wildlife is illegal in the State of California. Therefore, the provision of food for any wildlife is illegal.  The provision of food is not only illegal but it can also induce secondary pest problems like rodent outbreaks. The feeding of feral cats should also be strongly discouraged, particularly in areas where their feces could contaminate soils and other food.


Trapping can be a very useful tool for the management of rats in gardens. If you have a rat problem in your garden it is important to be realistic about the number of snap traps that will be required to manage the issue. One or two snap traps will not curb a population.  It is important to saturate an area with snap traps. Consider trapping at multiple levels also (inside beds, outside beds, on the ground, on fence lines etc.). Please be mindful of other community garden volunteers. It is important to let them know where snap traps are to reduce the risk of injury on encountering a snap trap.  If you are working in a school, snap traps can be set in the evening and checked in the morning before the children get to the garden. Snap traps should not be set in gardens during the day when children are present unless they are secured in trapping stations that can be provided under contract from a pest management professional. Snap traps can also capture nontarget wildlife such as birds and reptiles. Please be mindful of these when setting traps. Nontarget mortality can be reduced by trapping only at night or by using trapping stations that can exclude nontarget wildlife. It is not advised to live-trap any wildlife in a garden.  Once you trap a rat, under law, you must either release it right where you captured it, or euthanize it humanely.


The use of rodenticides to manage rats in and around gardens is actually not considered legal.  The majority of rodenticides available for purchase for unlicensed applicators are for structural use only.  It is permitted to have rodenticide in gardens as long as you are using it to control rodents that are invading a man-made structure such as a shed, storage barn, or building.  All rodenticides that are registered to manage rats must be applied in bait stations no more than 50ft away from the man-made structure, although some labels permit going further away (up to 100ft).


Placement of snap traps: (a) single trap with trigger next to wall; (b) the double set increases your success; (c) double set placed parallel to the wall with triggers to the outside.

Adapted from The Rat: Its Biology and Control, Howard, W. E., and R. E. Marsh. 1981. Oakland: Univ. Calif. Div. Agric. Sci. Leaflet 2896

Posted on Friday, July 13, 2018 at 6:08 PM
Tags: Community Garden (5), IPM (40), Rat Management (1), Rats (3), School Garden (6)

Congratulations, Frank Zalom: Editor-in-Chief of Journal of Economic Entomology

Frank Zalom, distinguished professor of entomology at UC Davis (shown here in an almond orchard) is the newly selected editor-in-chief of the Journal of Economic Entomology. (Photo by Kathy Keatley Garvey)

Congratulations to integrated pest management specialist  Frank Zalom, distinguished professor of entomology at the University of California, Davis, on his selection as editor-in-chief of the Journal of Economic Entomology, the largest and most cited of the family of scientific journals...

Frank Zalom, distinguished professor of entomology at UC Davis (shown here in an almond orchard) is the newly selected editor-in-chief of the Journal of Economic Entomology. (Photo by Kathy Keatley Garvey)
Frank Zalom, distinguished professor of entomology at UC Davis (shown here in an almond orchard) is the newly selected editor-in-chief of the Journal of Economic Entomology. (Photo by Kathy Keatley Garvey)

Frank Zalom, distinguished professor of entomology at UC Davis (shown here in an almond orchard) is the newly selected editor-in-chief of the Journal of Economic Entomology. (Photo by Kathy Keatley Garvey)

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