With Halloween coming up I am seeing lots of scary faux spiders among front yard Halloween decorations. I must admit I am guilty of feeding into the arachnophobia that so many people have by placing a big fake hairy tarantula in my yard.
Fascinating Creatures
Most spiders are solitary creatures, but some form groups and even cooperate in brood care, caring for other spiders' offspring.
Not all spiders spin webs but those that do can create an incredible assortment of web designs, depending on the species, including spiral orbs, funnels, tubular, or ground sheets.
In some cases, two or more males will perform for a female to compete for her favor.
Some drop their silk to act as parachutes so they can drift on the slightest breeze
While spiders do not have brains in the traditional sense, a type of jumping spider appears to remember similar prey it has encountered, using trial and error to determine what works in capturing it.
Common and Beneficial
Spiders are the most common miniature living things living in our homes (besides micro-organisms). We are seldom aware of them because they conceal themselves in hidden spots (thus camouflaging themselves from their prey), tend to be active at night, and avoid humans. After all, we are much bigger than they are!
Spiders are beneficial organisms because they feed on common indoor pests such as mosquitoes, flies, roaches, earwigs, and moths. An additional benefit: many of the indoor pests that spiders consume can transmit diseases, i.e., mosquitoes, fleas, flies, and cockroaches. If left alone, spiders will consume most of the insects in your home, thus providing effective pest control.
Spider Bites
The jaws of most spiders are too small to bite humans. Of those that can bite, they will bite only if provoked, but very few spider bites are dangerous to humans. If you are bitten, the bite area may swell slightly and itch.
The adult female black widow is the primary spider in California capable of seriously injuring people. If bitten, remain calm and seek medical help.
Contrary to common myth, the brown recluse spider does not reside in California.
Managing Spiders
If you do have a spider issue around your home, the most effective way to manage them is to do regular housecleaning. Sweep or vacuum up their webs both indoors and outdoors, and prevent clutter build up that can provide hiding places for them both indoors and outdoors. If you do come across one, capture it in a jar and release it outside in an out-of-the-way spot. Avoid using pesticides since the chemicals will also kill other beneficial insects.
Appreciate Spiders Beneficial Role and Help Protect Them!
I will continue to put out my big “scary” tarantula out with the Halloween décor because spiders are so awesome. However, I do not put out the fake webbing, because like real spider webs, they can trap beneficial insects, spiders, and even small birds such as hummingbirds.
I will continue to allow spiders to share my home and garden, so they can do their crucial work of reducing pests. I much prefer having a few spiders around than mosquitoes, flies, moths, or cockroaches!
You do not have to love spiders like I do, but I hope you can appreciate the vital role arachnids play in our homes and gardens, and generally let them be.
References:
Spiders: https://ipm.ucanr.edu/QT/spiderscard.html
Pests of Homes, Structures, People and Pets: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7442.html
Denise Godbout-Avant has been a UC Cooperative Extension Master Gardener since 2020.
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- Author: Denise Godbout-Avant
Why Are People Scared of Spiders?
One possible reason for people's fear of spiders is they are so different from the rest of nature, which Hollywood and the media have exploited.
Spiders are arachnids, a class of invertebrate creatures, which also includes mites, ticks and scorpions. Unlike insects, arachnids have eight or more legs, with two major body parts (insects have three), a fused head and thorax called the cephalothorax, and the abdomen.
Like mites, ticks and scorpions, most spiders are venomous, using venom to catch/kill their prey. However, the jaws of most spiders are too small to penetrate human skin. Only those spiders whose venom can cause a severe reaction are called “toxic” spiders.
Spiders in the World and California
Spiders have been around a long time – fossilized spiders have been found in 318-million-year-old rock. Today there are about 40,000 types of spiders in the world, on every continent except Antarctica. They range in size from a miniscule 0.02 inches (0.5 mm) to hairy tarantulas up to 3.5 inches (90 mm).
- California has quite a few tarantula species, none of which are venomous. They tend to be long-lived, and use silk to line their underground burrows.
- Orb weaver spiders are often large and colorful. Along with their distinctive, sizeable, elaborate webs they are easy to spot. Their venom is harmless to humans.
- Sheet web spiders are small brown spiders who build messy sheets of webbing, often on the ground. Their venom is harmless to humans.
- Cellar spiders, aka “daddy long legs” initially came from Europe, have long skinny legs, and often hang upside down. Their venom does not harm humans.
- Wolf spiders are free ranging predators who don't build webs and are harmless to humans.
Only four species of spiders in the world are really dangerous to humans: Sydney tunnel web spider (Australia), Brazilian wandering spider (Brazil), African sand spider, and widow spiders (global).
California's widow spider is the well-known adult female western Black widow (Latrodectus hesperus).
Their web is sticky, irregular and tough-stranded. During WWII widow silk was used to make the crosshairs in gunsights. Widespread in California, with as many as 20-30 per urban/suburban property, Black widows are found in the holes, crevices, trash, and clutter of human structures. Her distinctive shiny black body with a bright red hourglass on the underside of the abdomen is a warning signal to others which makes her easy to identify and thus avoid.
Misinformation on Spider Bites
Most spider bites cause no reaction or as much harm as a bee sting or mosquito bite. According to Spider Physiology and Behavior, Volume 41, there were only about 100 recorded deaths from spider bites globally during the entire 20th century! The last death by spider bite in California was in 1976 (due to septicemia). Other arthropod bites, including ticks, fleas, bees, wasps, bedbugs, mosquitoes, deer flies and horse flies, may be mistaken for spider bites.
A bite from black widow venom can cause fever, cramping muscle and joint aches, but it does not cause sores. But they are shy and reluctant to bite; when they do bite, it is often dry (no venom). On the rare occasion someone is injected with their venom, there is an effective antivenom available.
Brown Recluse Spiders
Management
Beneficial Spiders
Spiders are extremely beneficial due to being important predators of pest species. They are often the most important biological control of pests in and around homes, yards, gardens and agriculture. It is estimated that spiders eat 800 million tons of bugs a year. According to Norman Platnick of New York's American Museum of Natural History, “Spiders are primary controllers of insects. Without spiders, all of our crops would be consumed by those pests” and we could face famine.
I have always scooped up spiders I find in my home to carry them outside and will continue to do so. I am removing the spiders from my Halloween décor, since I do not want to continue misrepresenting these valuable creatures.
Resources
- UC Davis Dr. Lynn Kimsey's talk on spiders via UC IPM Urban & Community Webinars: https://www.youtube.com/watch?v=b6ExDP5wNVw
- UC IPM Natural Enemies Gallery https://www2.ipm.ucanr.edu/natural-enemies/spiders/
- UC IPM Quick Tips Card http://ipm.ucanr.edu/PMG/PESTNOTES/pn7442.html#SPIDER
- UC Riverside https://spiders.ucr.edu
- https://www.livescience.com/22122-types-of-spiders.html
- Author: Lynn S. Kimsey
- Posted by: Lauren Fordyce
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.
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
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.]
- Author: Alison Collin
This year appears to have produced a bumper population of Black Widow (Latrodectus) spiders. Having had too many close calls with these arachnids, I decided to eliminate as many as possible before I became a victim. I have no problems with other spiders and welcome them in the garden, appreciating their effect on the insect population and delighting in the beauty of a perfectly formed Orb spider's web. However, this summer it seemed that almost everything I touched had a Black Widow lurking underneath; when I filled my watering can one came out of the top as the water level rose, when I harvested my squash there was a large one under one of the fruits, the children's tree house had them in the corners, and as I was fitting a child's car seat into my car one emerged from under the seat as I tightened the final strap. Enough! I had to take action.
The first thing was to find out as much as possible about the habits and life cycles of the Black Widow, and the IPM website http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74149.html was invaluable for this. It shows photographs of not only adult female Widows with their shiny, black round bodies with the red hourglass markings on their lower abdomen, but also the male and immature forms, both of which look very different. Fortunately, these spiders are shy and tend to retreat to a hole or crevice if disturbed. This very habit means that the unwary may accidently disturb them and induce a bite – often by putting shoes on that have been left outside or by picking up such things as logs or pots that have one underneath. Their bite contains a neurotoxin which induces symptoms such as a localized rash, severe muscle cramps, possible paralysis of the diaphragm, nausea, vomiting, and changes in vision. Anyone bitten should use an ice-pack on the bitten area and then seek immediate medical help, if possible taking the culprit with them to confirm identification.
Black Widow spiders like to live in undisturbed clutter around homes and seem equally at home underneath garbage cans, under the covers of irrigation set-ups, in wood piles, in natural stone facing of retaining walls and houses, or in seldom-used children's' plastic toys where they build webs in the wheels and under seats. They are common in the darker corners of garages and sheds and will occasionally be found in similar spots inside homes. Their webs are not what we think of as the classic spider's web but rather a disorganized collection of very strong threads, often with bits of leaves or dead grass hanging in them and frequently containing small and very tough egg sacs which may contain up to three hundred eggs. The female can produce up to 10 of these from one mating! On average, they live for about three years. The population of these spiders is only maintained if there is enough food for them. It is not likely that there will be a shortage, since they will eat any insect: beetles, crickets, cockroaches and even scorpions.
I wanted to gain some control without the use of chemical sprays. I identified various webs, but as soon as I approached, the spiders would take cover in some inaccessible spot. Then a neighbor suggested that I go out after dark with a flashlight so, armed with an old shoe, I chose a warm moonlit night to begin my “Widow Vendetta”. I could not believe just how many spiders there were! On a raised planter bed with concrete stone edges, there was a large adult female about every 18 inches around the whole circumference. They were sitting in their webs upside down with their red hourglass markings clearly visible and they did not scuttle away when I shone the light on them, making a quick dispatch an easy matter. I then concentrated around the house foundations where there were dozens of tiny spiderlings setting up home. The flashlight had the benefit of casting their shadow onto the concrete path which made their exact position easier to see, and I often killed 30 spiders in one night. (I am relieved that this eccentric behavior has so far not appeared in the local “Police Blotter”)! I followed this routine every couple of weeks throughout the summer and swept the walls with a flat broom afterwards, which made it easier to spot new webs as they appeared. I have pruned vegetation back from beside the house and have tried to limit storage of items near entrances. A pressure jet of water could be used to dislodge some from more difficult positions, although that would surely be an egregious use of such a precious commodity during a drought.
Praying Mantises are particularly fond of these spiders, and some wasps parasitize them, so I am hoping that due to our combined efforts, we will gain some control. Meanwhile, I have been wearing gloves when performing gardening tasks, and have been carefully checking and brushing logs and plant pots before bringing them into the house. Only time will tell whether my efforts will make a noticeable difference to the Black Widow population, or whether I have upset the natural balance enabling some other noxious species to take hold instead.
For more info on Black Widows, see: http://www.livescience.com/39919-black-widow-spiders.html
When you see spiders in your garden, you may wonder if they can hurt you or your pets. The good news is, most spiders are not likely to bite or cause lasting harm if they do. Plus, they provide natural pest control! Here are a few spiders commonly found in gardens and landscapes:
Garden spiders or orb weavers spin funnel-shaped webs that cover plants or soil. This spider waits for prey to touch its web and then consumes it.
Crab or flower spiders look like tiny crabs. They use their enlarged front legs to stalk or hunt their prey.
Wolf spiders have long, hairy legs and don't build webs. They are often seen running along the ground.
Lynx spiders are active hunters that have spiny legs and a brightly colored body that tapers sharply toward the rear.
Black widow spiders are the only spiders in California that can be harmful to people or their pets. Venom from their bite can cause a mild to painful and serious reaction. However, death is highly unlikely, and symptoms can be alleviated with prompt medical treatment.
Wait, but what about the brown recluse spider? This spider isn't found in California. Yes, really. Read more in the Pest Notes: Brown Recluse and Other Recluse Spiders.
Watch this video to learn more about the spiders commonly found in gardens and sometimes inside the home.
You can also read the Pest Notes: Spiders for detailed information. For a colorful fact sheet, see the Quick Tips Common Garden Spiders.