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Landscaping for Spiders
by Carol O’Meara, Colorado State University Cooperative Extension

Landscaping for spiders? Why on earth would we want to? Simply put, gram for gram and fang for fang, spiders are the number one type of predator in the garden. These animals are not the bloodthirsty villains that Hollywood portrays - most of the spiders in Colorado are not harmful. Rather, they play a critical role in keeping insects down and feed our feathered friends as well. Birds rely on spiders for part of their diet and are benefited by gardens that have spiders.

Backyard gardens often have new growth that is a beacon for plant feeding insects. In many gardens, beneficial bugs have long been in vogue for controlling pests. Sadly, few folks will try to attract the best predators in the business – spiders.

Spiders are adapted to locate prey in all areas of the garden, making them ideal pest control patrols. Their method for capturing insects is widely varied and works on several levels: aerial webs capture flying insects, ground webs capture walking insects; while other spiders actively hunt. Many exploit landscape structures as camouflage, using blooms, bark, leaves or mulch as hiding places.

What attracts and keeps spiders in the garden? Location is a life or death decision for spiders. In landscapes that are exposed or without refuge, they are vulnerable to predators, heat, wind, and rain. The location must be near food since foraging is filled with peril and predators often attack unwary spiders. Spiders must outwit their enemies through misdirection or camouflage that can be unique or elaborate. For example, researchers are debating the role of web structures called stabilimentum, a thickened, often zigzag line of silk in the center of the web made by some spiders. One hypothesis is that this stabilimentum can mimic the body pattern of the spider, and misdirects hunting birds.

Providing plenty of food for spiders can be related to garden care. There is an interesting relationship between fertilizers and the herbivore/predator community. Fertilization stimulates new growth of plants, a favorite food of plant feeders. This flush of new growth stimulates a population explosion of plant feeding insects. Thus, a veritable buffet of healthy food for spiders is created.

Other landscape items that favor spiders:

Mulch - it buffers humidity, which is critical to spiders. Spiders cool themselves in two ways: retreating to shade or by evaporative cooling However, spiders do not sweat, and evaporative cooling means a release of water from the spider’s body from the mouth or special glands– a process that cannot be sustained for long, and uses critical water reserves. In Colorado, water loss without ready replenishment can be fatal to spiders. Fortunately, mulch can provide nooks and crannies for capturing and holding water. Mulch also provides retreats, houses ground dwelling prey, and provides anchor points for webs.

Foliage. A diverse garden will provide many types of spiders with their everyday needs. Such groupings of plants have foliage that provides shade, increases foraging areas, has nooks for holding water, provides food for the spider’s prey, and provides web anchor supports. In all, more diverse planting in gardens benefits the spider community.

Carol O’Meara is the Horticulture Assistant for Colorado State University Cooperative Extension in Boulder County. She is currently finishing her Master’s in Entomology at CSU.

The author is always willing to talk about spiders and questions are invited and encouraged. Please contact the Audubon Society for more information.