Arachnophobia: Should You Be Afraid of Spiders?

Fear of spiders, arachnophobia, is a widespread problem in western societies. This fear is not only of spiders but can extend to all land arthropods with more than six legs—the arachnids. It can range from simply avoiding arachnids to panic attacks, high heart rates, and flight behavior. It's not clear if arachnophobia is a learned response or something instinctive. However, it is much commoner in western societies than elsewhere. In other parts of the world, spiders may even be part of the diet. Fear of spiders can result in stress, wasted time, and environmental costs through overuse of insecticides. Insecticides are often used to kill spiders, but unless you directly spray the spider or its web, insecticides have little effect.

Most spiders, like this jumping spider, prefer to hide from people. [Credit: Dustin Hume, Unsplash]

What are arachnids?

Arachnids include spiders, mites, ticks, scorpions, harvestmen, whip scorpions, camel spiders, and vinegaroons. Of these, only spiders, mites and ticks, and scorpions have venom. Arachnids differ from insects in several ways. They have eight or more legs and two major body parts, the cephalothorax (a fused head and thorax) and abdomen. They don't have wings or antennae. Spiders are different from other arachnids because they can spin silk from structures called spinnerets at the end of the abdomen. They are much more commonly found in homes and gardens. Spiders do not have chewing mouthparts or legs modified to capture prey, so they rely on venom to both incapacitate their prey and begin digestion..

In California, spiders commonly encountered around buildings include jumping spiders, tarantulas, orb weavers, sheet web spiders, cellar spiders, wolf spiders and widow spiders.

Which spiders are dangerous?

Culturally, we're taught to fear certain spiders more than other arachnids, except for scorpions. Among these are black widows, brown recluse, and hobo spiders. Many issues are attributed to spider bites. However, in most cases of “spider bites” spiders were not actually involved. A sharp pain followed by development of a lesion or sore is not a sign of a spider bite but could instead be due to a staph or strep bacterial infection.

Humans are largely unaffected by the venom of most spider species. During the entire 20th century, only about 100 deaths from spider bites occurred worldwide.

Only a few spiders have venom that is dangerous to humans, including the Sydney funnel web spider of Australia, widow spiders (Latrodectus), Brazilian wandering spider, and the African sand spider.

Widow spiders

The only potentially dangerous spiders in California are widow spiders. Both the native western black widow spider and the invasive brown widow spider occur in California. These are smooth bodied, shiny spiders, with long slender legs, and a bulbous abdomen in the females. They appear to be hairless. Females have a bright hourglass shaped mark on the underside of the abdomen.

Widow spiders make messy webs in sheltered sites. The silk is several times as strong as silk produced by other spiders and has a different feel when touched. These tough silk threads are also smooth and homogeneous. During WWII widow silk was used to make the crosshairs in gunsights for the U.S. Army.

Widow spiders are abundant in urban and suburban habitats. In some regions of California there might be as many as 20 to 30 black widows per property. They are shy, reclusive spiders and live in quiet dark places. They generally retreat into hiding places when confronted by any animal larger than they are. Actual widow bites are rare and rarer still do they inject venom. Instead many widow bites are what are called dry bites. Black widow venom is neurotoxic and can cause fever, muscle and joint aches and muscle cramping. It does not cause sores, and it is rarely fatal. There is an effective antivenom available for treating black widow bites.

Recluse spiders

The brown recluse spider is not found in California. [Credit: Ed Freytag, Bugwood.org]

Recluse spiders also have bad reputations. These are ground-dwelling spiders in the genus Loxosceles that somewhat resemble wolf spiders. There are several species across the U.S., but only two occur in California, L. deserta and the introduced L. laeta, but most people focus on the brown recluse, L. reclusa. California has the largest number of diagnosed brown recluse spider bites in the U.S., yet the brown recluse does not occur within 1,000 miles of California. Essentially, all recluse bites in California are probably bacterial infections.

True to their name, recluse spiders are very shy and occur in dark quiet places. Recluse spiders appear to be even more reluctant to bite than widow spiders. In an example of this, in the early 2000's a Kansas family began collecting spiders in their century old farmhouse. After one year they had collected more than 2,000 brown recluse spiders. No one had ever been bitten.

Hobo spiders

Hobo spiders, Eratigena agrestis, are found in Washington and Oregon, and perhaps far northern California. This spider is also a ground dweller and resembles a small wolf spider. Online, its bite is said to be as dangerous as recluse spiders, causing necrotic sores. This is also an urban myth. Sores attributed to hobo spiders are generally caused by bacterial infections.

For more information on spiders, see Dr. Kimsey's webinar on the UC IPM YouTube channel.

[Originally featured in the Fall 2022 issue of UC IPM's Home & Garden Pest Newsletter.]

Originally posted on the UC Master Gardener Program Statewide Blog

Poinsettia plants, Euphorbia pulcherrima, has toxic white sap.

During the holiday season many plants, cut flowers and flowering bulbs are used as decoration and given as gifts.  Many of these items can be poisonous to both humans and pets with long-term negative effects to one's health.  Plant poisoning can range from simple rashes and blisters all the way to organ damage and in severe cases death. Be safe this holiday season by being mindful of what plants and flowers you are either giving, receiving or decorating with.  Common holiday plants that pose a toxic risk are: Amaryllis (bulb portion), Chrysanthemums, Holly (berries), Mistletoe (berries and leaves) and Poinsettia.

The entire mistletoe plant, Viscum album, is considered toxic.

Simple steps can be taken to help minimize the risk that poisonous or toxic plants cause when brought into the home. 

• Know what plants you have in your home and the health risks they pose
• Place poisonous plants out of reach of children and pets
• Teach children not to put any part of a plant in their mouth
• Discard plant leaves and flowers in a safe way so that children and pets cannot get to them
• Use protective gloves and clothing when handling plants that may be irritating to the skin
• Wash your hands after handling plants
• Don't garnish food trays or tables with poisonous plants

Amaryllis plant, Hippeastrum sp., have toxin primarily in the bulb but also in the leaves and stems.

Signs of poisoning range from dizziness, nausea, vomiting, diarrhea or stomach cramps.  Some plants can cause irritation to the skin, mouth and tongue and immediate burning pain. The signs of poisoning may not appear immediately so if you suspect that someone has been poisoned by a plant, telephone your doctor or the Poison Control Center 1-800-222-1222.  If you are advised to go to an emergency room, take the plant or a part of it with you (take more than a single leaf or berry). Take the label, too, if you have it. The correct name can result in the proper treatment if the plant is poisonous. If the plant is not dangerous, knowing the name can prevent needless treatment and worry.

Mum plants, Chrysanthemum sp., have toxic parts above ground.

Resources:

To view a list of safe and toxic plants for humans please visit:  http://ucanr.edu/sites/poisonous_safe_plants/

To view a list of safe and toxic plants for animals please visit: http://ucanr.edu/sites/poisonous_safe_plants/Plant_Toxicity_Levels_523/

For houseplant pest problems visit: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74172.html

Pittenger, Dennis. California Master Gardener Handbook--2nd Ed, Davis, UC Agriculture and Natural Resources, 2015.

Invasive plants don't get much coverage in the news, especially at the state and national level.  As I've argued previously, this lack of media attention is a problem when it comes to motivating the public and political players into proactively funding invasive plant management and mitigating impacts to human health, infrastructure, and natural resources.  Admittedly, as a weed scientist, I'm biased on the issue.  

However, sometimes there is a particular plant that is just so terrifying that it lends itself to coverage in a major news outlet, as was the case for this article about giant hogweed (Heracleum mantegazzianum) by Caitlin O'Kane on CBS news last month: "Giant hogweed, plant that causes blindness and third-degree burns, discovered in Virginia."  As the headline suggests, this is a plant you should keep a safe distance from if you are unlucky enough to come across it.  Just in case you're thinking that this is just sensationalism, there's a page on Snopes that confirms the assertions about giant hogweed's dangerous sap (and also confirms its place in popular culture).  I won't provide a direct link here, but a simple Google search of "giant hogweed" turns up some images of what look like very painful giant hogweed injuries.  The photograph below was taken by Gavin Edmondstone:

Giant hogweed is native to the Caucasus region and southwest Asia, and is presently found in Europe, Canada, the United States,  Australia, and New Zealand, where it was likely introduced as an ornamental for its showy inflorescence.  Apparently it was a well known nuisance in Britain, so much so that the band Genesis released the ominous song "Return of the Giant Hogweed" on their 1971 album Nursery Cryme:

"Turn and run
Nothing can stop them
Around every river and canal their power is growing..." (Google the song title for the complete lyrics- they are fantastic!  And strangely factual...)

Here in the US, giant hogweed is mostly found in New England and the Pacific Northwest.  As the article suggests, giant hogweed has expanded down the east coast and was recently discovered for the first time in Virginia.  Over on the west coast, it has made it as far south as northwestern Oregon.  Californians should be on the lookout however, as we do share some similar habitats with Oregon, particularly in the northern part of the state.  California also has a native congener called "cowparsnip" (Heracleum maximum), suggesting that suitable habitats do exist across the state.

For those involved with management of this plant, a great resource with information on controlling giant hogweed can be found in DiTomaso et al. (2013) Weed Control in Natural Areas in the Western United States, as well as several state conservation webpages.  Before embarking on control, be careful not to confuse with natives that may look similar- your local county Natural Resources Advisor can be of great help in correctly identifying invasive plants.  And it should go without saying, but given the potential for painful injury, this is a plant you may want to enlist the help of professionals with if you have it on your property.

As the band Genesis proclaims:

Now if we could just get some similar coverage in the press or popular culture for our less glamorous but equally terrifying invasive grasses...

Invasive plants don't get much coverage in the news, especially at the state and national level.  As I've argued previously, this lack of media attention is a problem when it comes to motivating the public and political players into proactively funding invasive plant management and mitigating impacts to human health, infrastructure, and natural resources.  Admittedly, as a weed scientist, I'm biased on the issue.  

However, sometimes there is a particular plant that is just so terrifying that it lends itself to coverage in a major news outlet, as was the case for this article about giant hogweed (Heracleum mantegazzianum) by Caitlin O'Kane on CBS news last month: "Giant hogweed, plant that causes blindness and third-degree burns, discovered in Virginia."  As the headline suggests, this is a plant you should keep a safe distance from if you are unlucky enough to come across it.  Just in case you're thinking that this is just sensationalism, there's a page on Snopes that confirms the assertions about giant hogweed's dangerous sap (and also confirms its place in popular culture).  I won't provide a direct link here, but a simple Google search of "giant hogweed" turns up some images of what look like very painful giant hogweed injuries.  The photograph below was taken by Gavin Edmondstone:

Giant hogweed is native to the Caucasus region and southwest Asia, and is presently found in Europe, Canada, the United States,  Australia, and New Zealand, where it was likely introduced as an ornamental for its showy inflorescence.  Apparently it was a well known nuisance in Britain, so much so that the band Genesis released the ominous song "Return of the Giant Hogweed" on their 1971 album Nursery Cryme:

"Turn and run
Nothing can stop them
Around every river and canal their power is growing..." (Google the song title for the complete lyrics- they are fantastic!  And strangely factual...)

Here in the US, giant hogweed is mostly found in New England and the Pacific Northwest.  As the article suggests, giant hogweed has expanded down the east coast and was recently discovered for the first time in Virginia.  Over on the west coast, it has made it as far south as northwestern Oregon.  Californians should be on the lookout however, as we do share some similar habitats with Oregon, particularly in the northern part of the state.  California also has a native congener called "cowparsnip" (Heracleum maximum), suggesting that suitable habitats do exist across the state.

For those involved with management of this plant, a great resource with information on controlling giant hogweed can be found in DiTomaso et al. (2013) Weed Control in Natural Areas in the Western United States, as well as several state conservation webpages.  Before embarking on control, be careful not to confuse with natives that may look similar- your local county Natural Resources Advisor can be of great help in correctly identifying invasive plants.  And it should go without saying, but given the potential for painful injury, this is a plant you may want to enlist the help of professionals with if you have it on your property.

As the band Genesis proclaims:

Now if we could just get some similar coverage in the press or popular culture for our less glamorous but equally terrifying invasive grasses...