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Pest Control/Western-spotted Orb Weavers


I work at a wastewater treatment plant, and we are inundated by orb weavers [which were identified by someone from this site sometime ago.

We can't use harsh insecticies to try to get rid of them - or at least keep them at bay.  They primarily live in a concrete stucture, with a million nooks-and-crannies.

I'm just curious if they have any natural predators, that also native to Southern California. Or if there is a habitat that would be encourage them to leave?


Massive spider "outbreaks" and webbing are common at waster-water treatment facilities because the highly organic open water supports large numbers of aquatic insects like midges. These in turn are prey for the spiders. The spiders are completely harmless but the best way to reduce their number is to cut back on outdoor lighting which attracts the aquatic insects and "feeds" the spiders. My guess is you see the most webbing near outdoor lighting. There are no insecticides that can be legally used against these spiders because the spiders are non-venomous and in fact beneficial.

Jack DeAngelis

Pest Control

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Jack DeAngelis


I can answer questions about the control of pest insects, spiders, mites and related arthropods. These household pests include termites, carpenter ants, powderpost beetles, nuisance ants, bed bugs, cockroaches, fleas, wasps, and many others. I can also answer questions about using pesticides and other pest control tools such as baits and traps.


I am a retired university extension entomologist. I've taught and conducted research in urban and agricultural entomology. I've published over 70 extension publications, 20 research publications and several books about insects.

Ph.D. in Entomology

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