Green Blog

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.

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.

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.

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.

Organic farmers and researchers strive to advance soil care

Organic farmer Phil Foster has developed a creative way to nurture the soil on his 200-acre farm near Hollister. He plants cover crops in a single line at the top of the planting bed, saving water and seed while keeping the furrows clear for irrigation.

"We were finding we couldn't use cover crops because of water," Foster said. The narrow strip makes the best use of the limited water supply, while garnering the benefits of cover crops - which buffer soil temperatures, inhibit weeds, increase soil microbial activity, improve water infiltration and add nutrients. Growing cover crops prepares the soil for the production of high-quality vegetables.

Foster is one of eight organic vegetable growers who are working with researchers at Chico State, Fresno State and UC Agriculture and Natural Resources on a project funded with a USDA grant designed to make significant improvements in soil care in organic production systems. He guided project participants around his farm, equipment yard and compost operation in early November to share the techniques he and his staff have developed over three decades to promote soil health.

Tour participants marveled at the soil characteristics, admiring tiny pores and roots in clods of dirt, evidence of the soil's capacity to move water and nutrients. They studied the plant and soil conditions after farm manager Efrain Contreras pulled a carefully crafted implement for rolling down the cover crop across the field with a tractor. 

Foster credited Contreras, a 30-year employee, for his role in building the soil on the farm. Labor, Foster said, is his biggest cost. He has 50 full time staff, many with 5 to 20 years of experience.

"They are the key to to the success of the ranch," Foster said.

Minimizing and, eventually eliminating, soil disturbance can be combined with organic groundcover, year-round root growth and robust biological activity in the soil to further promote soil health. Following the tour, the farmers talked about ways to attain the goal on their farms of no-till organic vegetable production. 

Foster said he will experiment with reducing soil disturbance to determine whether doing so will maintain or increase yields. Another farmer in the project, Scott Park of Meridian, Calif., 50 miles north of Sacramento, said he will dedicate eight acres of his organic farm to comparing the results when the cover crop is chopped and left on the soil surface to chopped and incorporated with tillage.

Paul Muller and Andrew Braitt of Fully Belly Farm in the Capay Valley suggested the researchers could help the farmers by identifying optimal, effective cover crop rolling techniques. Retired organic farmer Tom Willey of Madera suggested grant funds be used to purchase appropriate scale cover crop seeders for on-farm experimentation.

"We're making great progress," said project coordinator Jeff Mitchell, UC Cooperative Extension vegetable crops specialist. "By getting together regularly, we're seeing opportunities for moving further toward reduced-disturbance on the farms, identifying the equipment needs and establishing effective channels of communication."

Over the project's three-year term, the farmers and researchers will continue to experiment with soil-building techniques and share results.

 

 

   

Catastrophic wildfires and climate change lead to growing acceptance of ‘pyrosilviculture’

For millennia, fires periodically burned through California forests, thinning trees, reducing shrubbery and clearing out downed branches and debris. Without periodic fire, the forests became more dense, with spaces between large trees filling in with a thick carpet of duff, seedlings and shrubs.

As a result, today's forests are prone to more intense and damaging fires, like the Rim Fire, King Fire, and — most recently — the Camp Fire in Butte County. These fires are burning with unprecedented severity and speed, threatening large swaths of forest, towns, and even urban areas.

Using fire as part of forest management is not a new concept. Native Americans were known to burn brush to open up hunting grounds and clear shrubbery for gathering. Decades ago, iconic Berkeley forestry professor Harold Biswell said, “Fire in the Sierra Nevada is as important as rain.”

Competing forces, however, pushed foresters and fire officials toward fire prevention and suppression, particularly the cataclysmic fires of the early 20^th century that leveled entire towns and left dozens of residents and firefighters dead. The fear of out-of-control blazes and the perceived damage to timber resources launched a war on fire that has lasted a hundred years. Some forest managers are urgently trying to negotiate a truce.

Making peace with fire and turning it into a useful tool, rather than a raging threat, was the objective of an October meeting in Shaver Lake of UC Cooperative Extension forestry and natural resources scientists, Southern California Edison forest managers, CALFIRE officials and U.S. Forest Service representatives.

The event also raised awareness of “pyrosilviculture,” a new forest management term coined by UC fire scientist Rob York to emphasize the importance of fire in silviculture, the management of forests for wood.

Forests have myriad benefits – recreational, environmental and economic. Nature lovers value the whisper of pine trees in the wind and green shade over hiking trails and ski slopes. Owls, bears, deer and other wildlife make their homes among firs, pines, oaks and cedars. Forests stabilize mountain slopes, which store water as snow for agriculture and drinking. People build their homes, businesses and schools out of the planks and boards cut from the straight, soft wood of conifer trees.

The value of California forest products was about $429 million in 2017, according to the USDA. Because fires can damage and destroy trees, the timber industry has historically been reluctant to use fire as a tool. That's changing.

“Fire is such an important ecological process, you can't manage for timber without fire,” York said.

York is the manager of the Blodgett Forest Research Station, UC Berkeley's 4,000-acre mixed conifer and oak forest near Georgetown where researchers study forest management practices for increasing timber yield while taking advantage of fire to enhance forest health and make forest stands more resilient to wildfire.

Controlled burning can be used to treat fuels and reverse these trends, but it has been inhibited by a number of barriers, including landowners' concerns about liability, risk aversion among fire management agencies, narrow burn windows, air quality limitations and other regulatory challenges. Now, public demand for prescribed fires is growing.

“I believe what moved the needle was, for several years in a row, there were high-severity fires in the news,” York said. “Wildfires were in the pubic zeitgeist. People began asking, ‘Why aren't we doing more prescribed fire?'”

Climate change is also intensifying the interest among the public and silviculture professionals. Because California is getting warmer and fire seasons are growing longer, high-severity fires are expected to increase.

“There would logically be a tipping point. Even though we reduce the growth of trees when we use fire, if it can prevent the loss of the forest entirely, it would be meeting the timber objective,” York said.

The vast tree die-off during the 2011-2016 drought was another jarring sign that the Sierra Nevada ecosystem is out of balance.

The U.S. Forest Service, which manages 20 million acres of forest in California, is using prescribed fire to reduce fire risk on federal forestlands, but scientists say it's not nearly enough to reduce the threat of catastrophic wildfire. CAL FIRE is ramping up its controlled burn efforts, but it will take time to address far-reaching areas of overgrown forestlands. The agency sometimes uses mechanical measures such as mastication and chaining before burning to pre-treat fuels and prepare units for burning.

“We need to work around communities first, and then move out to the wider landscape,” said CAL FIRE division chief Jim McDougald. “If a prescribed fire moves into a subdivision and burns houses, we take 100 steps back.”

UC Cooperative Extension is working with private landowners to encourage more prescribed burning to reduce fire risk, protect communities and timber. UCCE forestry and natural resources advisor Susie Kocher coordinated training sessions this year in four mountain communities. The sessions included local fire history and current fire research, prescribed fire permitting and legal considerations, fire weather forecasting and online tools, air quality and smoke management, fire terms and fire behavior, burn plan development, burn unit preparation and fire tools and equipment.

“Burning is a key element of forestland management and it can be safe if done properly,” Kocher said. “We provide classroom instruction and invite participants to join a live prescribed fire at Blodgett Forest as part of their training so they become familiar with the process.”

At the training sessions, UC Cooperative Extension advisor Lenya Quinn-Davidson said that in some cases, private landowners can conduct burns themselves. In her hometown in Trinity County, many ranchers and landowners conduct small broadcast burns to reduce fuels and improve forage. These burns are typically quite small and usually conducted in the winter.

“This can be a good option for landowners who wish to burn small areas, but we need other options for bigger, more complex burns” Quinn-Davidson said.

In other parts of the country, landowners have formed Prescribed Burn Associations (PBAs) that allow landowners to work with neighbors and other community members on controlled burns, sharing equipment and labor while developing skills. The PBA model provides a low-cost, grassroots option for prescribed burning, and empowers landowners to work together, and with other key experts and partners, to bring fire back to the landscape, says Quinn-Davidson.

“People are desperate to do something about fire, and the PBA model gives them an option to actively engage with each other and with fire as a tool—it's very empowering,” said Quinn-Davidson.

 

Communication is key to action on California’s new water narrative

UC scientists, students and water agency professionals took a critical look inwards and a radical look outwards when they gathered in Sacramento in October to reimagine California water.

The event was the fourth annual gathering sponsored by UC ANR's California Institute for Water Resources and the University of California Water Security and Sustainability Research Initiative, UC Water.

While science is the hallmark of a research-oriented institution like UC, the participants were asked to recognize their important role not just as scientists but also communicators.

“We have a big role in educating the public,” said Roger Bales, engineering professor at UC Merced who has been active in water and climate research for more than 30 years. “Scientists are political actors. Facts do not speak for themselves.”

Felicia Marcus, chair of the California Water Resources Control Board and a conference panelist, asked the scientists to make their work accessible, and if they are uncomfortable with plain language, “write it both ways.”

“Complexity can lose people easily,” she said.

The conference keynote speaker, futurist Kim Stanley Robinson, also addressed the divide between scientific discourse and popular understanding, in particular when speaking about climate change.

“There is a strange disconnect between what the scientific community is telling the world and what the world is hearing. As a result of data analysis, science is announcing to the world there is climate change. Individuals cannot perceive climate change,” he said. “Show them in ways that can be understood by the senses. The story has to be told with pragmatism and common sense.”

The Reimagining California Water Conference pursued the water journey from the high-mountain headwaters of the Sierra Nevada to the vast groundwater basins in the valleys below. Over the last century, the mountains were blanketed with snow each winter, storing water that melted slowly in the spring and summer to provide a reliable source of water for farming and communities below. However, climate change is telling a new tale. Warmer weather means less snow and more rain will fall on the mountains during the winter. The quick runoff must be managed in a way that preserves it for use in the summer.

“We need groundwater recharge because we're losing the snow pack quicker than we thought we would,” Bales said.

The new California water narrative has prompted scientists and policy makers to take a serious look at the potential for “flood-managed aquifer recharge” or Flood-MAR. Flood-MAR is a management strategy that uses water from rain or snowmelt to flood agricultural lands and working landscapes, such as refuges, floodplains and flood bypasses.

Successful implementation of Flood-MAR requires the identification of land for groundwater recharge, understanding the economic and agronomic impact of using agricultural land for recharge, and impacts of high-volume recharge on groundwater quality. But the potential is enormous.

“The state's underground basins are capable of storing 500 million acre-feet of water,” said Graham Fogg, UC Davis professor of hydrogeology. “That's like 500 Folsom reservoirs.”

Though the enormity of rewriting the California water story might seem an insurmountable challenge, panelist Debbie Franco noted that the passage of Sustainable Groundwater Management in 2014 happened when the state's unsustainable reliance of groundwater spiked during the 2011-2016 drought, reducing municipal water quality, drying domestic wells and causing land to sink.

“What seems impossible, after four years of drought, can be possible,” Franco said. “What will be the next thing? Get a sense of the solutions now.”

Change on the range

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