Spiders

Spiders in the garden may provide a frightful shock for those on the phobic end of the arachnid spectrum. For the rest of us, seeing spiders indicates a healthy ecosystem with plenty of biodiversity. How do spiders help your garden and which ones should you be worried about?

Woodlouse spider © Hans Hillewaert CC BY-SA 3.0

What makes a spider a spider?

Spiders are not insects, even though they have exoskeletons, jointed bodies, and appendages. Spiders and insects are both arthropods. The difference is that spiders have six or eight eyes, eight legs, and fangs that inject venom, which insects do not. Also, spiders do not have antenna (though there are spiders who pretend to be ants by holding their front legs to make them look like antennae).

Spiders and scorpions are both members of the arachnid class. Spiders have a more centralized nervous systems than other arthropods, and they move their limbs using hydraulic pressure, rather than muscles. The webs we see are produced from glands that make silk that is spun into threads using spinnerets. There is a wide variety of web sizes, shapes, and styles within the spider community. Did you know that spiders tune their webs to specific frequencies?

Tiny male Golden orb weaver (top) protected from the female by producing the right web vibrations and being too small to be worth eating. (DirkvdM) CC BY-SA 3.0

Common spiders

Below is a list of the common types of spiders found win North America:

• Funnel weavers, or grass spiders (Agelenidae) - webs commonly seen on low vegetation
• Orb weavers, or garden spiders (Araneidae) - concentric circle webs capture flying insects
• Sac spiders, or two-clawed hunting spiders (Clubionidae) - nocturnal; stalk prey
• Dwarf spider (Linyphiidae, aka Microphantidae) - sheetlike webs; diurnal
• Wolf spiders (Lycosidae) - actively hunt on the ground, day or night, live in burrows; and they have eyes on the back of their heads!
• Lynx spiders (Oxyopidae) - stalk and capture hunters
• Jumping spiders (Salticidae) - webless, daytime spiders
• Cobweb weaver, or clubfooted spiders (Theridiidae) - hangs upside down on sticky webs
• Crab spider, or flower spider (Thomisidae) - longer front legs, diurnal, flattened body

Spider behavior

Except for one herbivorous species that was identified in 2008, all spiders are predators. These beneficial insects hunt and feed on insects and other spiders, and some of the larger varieties hunt lizards and birds. (Yikes!) The familiar sticky webs are not the only way spiders capture their prey. Some species use a lasso, while others mimic their prey to get close enough to grab them, and others actually chase their prey down before injecting them with paralyzing venom.

After capturing a meal, spiders must inject victims with digestive enzymes, because spider guts are too narrow to process solids - they actually have filters on their faces that prevent solids from getting in.

Some species of spiders form social groups of up 50,000 individuals, but most spiders are solitary. Spiders generally only live for two years, but some captive species have lived as long as 25 years. According to Wikipedia, “Male spiders identify themselves by a variety of complex courtship rituals to avoid being eaten by the females.” (Sorry guys, I couldn’t resist.) Anyway, recent research has shown that spiders eat more than insects and other spiders: many species also drink nectar, And young spiders that eat pollen have been shown to have higher survival rates than those who do not. Some spiders are scavengers, eating dead insects that they find. Captive spiders have even been observed feeding on egg yolk, sausages, milk, bananas, and marmalade.

Good spiders

Scary looking or not, spiders help us fight many garden pests without the use of chemical pesticides. In fact, spiders are believed to be the most beneficial insect we can have in the garden! Spiders commonly eat earwigs, roaches, flies, moths, mosquitoes, aphids, caterpillars, cucumber beetles, grasshoppers and crickets, pine sawflies, redhumped caterpillars, armyworms, leafhoppers, spider mites, thrips, leaf miners, spruce budworms, tobacco budworms, sorghum midges, and fleahoppers. (It may have been easier to list what they don’t eat!) Spiders also eat other beneficial insects, but the damage they prevent far outweighs the damage they do.

Most types of spider venom are not dangerous to people, with the few exceptions listed below. In fact, research is being conducted to explore the use of spider venom as both pesticide and medicine.

​Bad spiders

While spiders are a great addition to any garden or landscape, there are a few exceptions. Black widow, recluse, and funnel spider bites can cause life-threatening reactions. That being said, only 100 deaths occurred in the 20th century due to spider bites, while 1,500 people died during the same time frame from jellyfish stings. Weird. Anyway, most spider bites are much like bee stings - they hurt like crazy, at first, and then go away. You can reduce the discomfort by cleaning the area, applying antiseptic, and then ice to the area. If unusual or severe reactions occur, get to the hospital as quickly and as safely as you can or call poison control (in California, that number is 1-800-222-1222). If you don’t have the number for Poison Control in your contacts, you should do that now. Really. By the way, if you do get bit by a spider, try to capture it for identification. Your doctor will thank you.

There are very few poisonous (to people) spiders in California. These include:

• Black Widow (Latrodectus hesperus) — female widows are shiny black, with slender legs, and a red or orange hourglass shaped mark on the underside of the large abdomen. Young female widows have the markings on top. Males have smaller yellow belly marks, but they generally can’t bite you. Webs are irregular and tough. Widows prefer dark, dry, undisturbed locations, such as garages, sheds, wood piles, and utility boxes. Wearing gloves and long-sleeved shirts, and being observant, are the only protection needed.

Female black widow (Ken-ichi Ueda) CC BY 4.0

• Yellow sac spiders (Cheiracanthium inclusum) are the ones responsible for spinning those webs you find where walls meet the ceiling. Predominantly an indoor spider, they may also be found in shrubs. Being indoor spiders, they are believed to be responsible for more spider bites than any other species. These spiders drop to the floor and run for it when disturbed. 

Yellow sac spider (Judy Gallagher) CC BY 2.0

• Recluse spiders - there are several types of recluse, most of which are not found in California. They all feature a violin-shaped mark on top of the head, but it is not always visible. Recluse spiders make large, irregular webs. The infamous brown recluse (Loxosceles) does not occur here. The less dangerous native desert recluse (L. deserta) is found in southern California. The imported Chilean recluse (L. laeta) is potentially deadly, but no bites have been reported.

Chilean recluse (Mampato) CC BY-SA 3.0

If you see spiders in the garden, be glad for the help they provide. And consider this:

In the 16th century, monks would go out into forests and fields to collect spider webs to use to make gossamer canvases for religious paintings. (And we thought plastic wrap was hard to work with…)