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Spiders are best insect-control weapons in gardens
Since spiders actively hunt or spin webs to trap insects, invertebrates, and even small vertebrates like lizards and frogs, it makes them garden-friendly.

Although many people have a built-in aversion to them, spiders rank as one of the gardener’s best tools for biological pest control.

They also are one of the few pest predators that don’t eat plants.

Evan Lampert, an associate professor of biology at the University of North Georgia Gainesville in Oakwood, described spiders at generalist predators.

“They can feed on variety of different types of prey,” he said. “Spiders will eat anything they can.”

Examples are beetles and larvae, grasshoppers, caterpillars and aphids. They will also consume spider mites, slugs and snails.

“Jumping spiders love caterpillars,” Lampert said. “Larger spiders will eat grasshoppers and eat things that fly like moths that lay eggs.”

Since spiders actively hunt or spin webs to trap insects, invertebrates, and even small vertebrates like lizards and frogs, it makes them garden-friendly, said Linda Rayor, an assistant professor of entomology at Cornell University.

“Spiders eat the (equivalent insect) weight of all the humans on earth annually,” she said. “A significant percentage of those insects are herbivores or granivores (seed eaters) or other insects that adversely affect humans. Spiders perform a vital function.”

Lampert agreed, explaining spiders will suppress the insect population without causing damage to the plants.

“One of the good things about spiders is they are insect controls,” he said, adding spiders to feed as much as others. “Spiders can hang out until there is prey and stick around whereas other predators leave.”

More than 45,500 known spider species are around the world and divided into 110 spider families, Rayor said.

And the most important fact is very few spiders are medically harmful, Lampert said.

“Even though most spiders are venous, only four species are dangerous,” he said, pointing out only a couple — the black widow and brown recluse — reside in Georgia.

“None are aggressive,” Raynor said

Lampert said spiders will build webs in relatively concealed areas such as underneath a gate or fence and around a deck.

“Houses and edges of houses are perfect for black widows,” Raynor said. “They can build underneath and protect their webs.”

Spiders, including black widows, respond to movements in their webs, and that leads to people getting bitten, Rayor said. Lampert encourages homeowners to leave them alone.

“Widows bites are painful, but it is only likely to harm child or elderly person,” he said. “It hurts like crazy. But there is an antivenom to widow bites.”

Spiders also are not a good choice for taking out specific plant pests in fields or gardens if there’s a particular outbreak you’re trying to eradicate, Rayor said.

“But for reducing all prey abundance in certain areas, they’re great,” she said.

Rather than try to eliminate spiders in or near homes, the knowledgeable, organic-leaning gardener prefers to recruit them.

“In general, the best way to encourage (spiders) is to have a lot of plant diversity,” Lampert said. “The more you have, the more the more ecological niches can be filled.”

You can increase spider numbers in the garden by:

* Adding more trees, shrubs and perennials to provide anchor points for web-building spiders to spin their webs, said Gail Langellotto, an entomologist with Oregon State University’s Extension Service.

* Allowing areas to go untilled, or leaving plant stalks standing for overwintering habitat. Many adult spiders emerge in early spring, before most other bio-control resources are available.

* Mulching with grass or wood chips to provide cover and humidity.

* Growing flowers that attract insect prey.

“Even if you want to bring spider numbers down around your property, consider that they’re difficult to eradicate with pesticides,” Langellotto said.

“The amount and concentration needed is often higher than what’s necessary to kill insects, (and that) poses a greater risk to humans,” she said. “Heavy doses also will kill a lot of other beneficial insects.”

Life Editor J.K. Devine contributed to this story.