Garden spiders

How it works

Spiders are arachnids, not insects: eight legs, two body parts (a combined head and thorax, and an abdomen), and no wings or antennae. Garden spiders hunt in two broad ways. Web-builders wait for prey: orb weavers spin the familiar wheel-shaped web, sheet-web weavers lay flat sheets over plants, and cobweb spiders hang upside down in tangled, sticky webs. Hunters go after it: jumping spiders stalk and pounce from many times their own body length, wolf spiders run their prey down on the ground, and crab spiders have enlarged front two pairs of legs that extend out to the sides.

They matter because there are so many of them. Nyffeler and Birkhofer estimated in 2017 that the world's spiders kill 400–800 million tons of prey a year, and cited exclusion experiments in which plant- and debris-feeding insects and springtails increased significantly once spiders were removed. Most of that kill happens in forests and grassland; spiders in annual crop fields account for less than 2% of it. A 2019 review in Oecologia describes spiders as among the most abundant and diverse natural enemies on farms, with evidence for their role in pest suppression still accumulating. The same review stresses the catch: as generalists, they can also disrupt the control provided by other natural enemies. In a pitfall-trap study of 19 urban gardens in central California, spider activity and species richness rose with mulch cover and the number of flowering plant species, and fell with bare soil.

What it is confused with

The webbing on a plant is usually what raises the question. Most garden spiders cannot even pierce adult skin. The two covered here, the black widow and the brown recluse, are the dangerous species described in UC IPM's and Kentucky Extension's fact sheets.

1. PestSpider mite webbing — Silk webbing over infested leaves, dense enough to cover leaves and twigs when mites are heavy, with pale stippling on the leaves. A spider's web has a spider in it, and the leaves around it are not stippled.
2. PestBlack widow — Shiny black, with a red hourglass on the underside of the abdomen. UC IPM says it is found outdoors in sheltered, dry, undisturbed places such as woodpiles and garages.
3. PestBrown recluse — A violin-shaped mark on top of the head region, with the neck pointing backwards, and six eyes in three pairs. It lives in the south-central and Midwestern US and does not occur in California. Kentucky Extension says many harmless brown spiders are mistaken for it.
4. Also goodOther brown garden spiders — Wolf spiders, ground spiders and most other brown spiders in beds and mulch are hunters, not recluses. Kentucky Extension says many harmless brown spiders are mistaken for the recluse, and suspected bites outside its native range are particularly unlikely.