November 28, 2021

McKenzielee Blog

Wicked Clever House Experts

Garden spiders are missing this fall; how can we bring them back to our yard? Ask an expert

5 min read

We’re well into fall, but there are plenty of things still to do – or just dream about. You may have some questions. For answers, turn to Ask an Expert, an online question-and-answer tool from Oregon State University’s Extension Service. OSU Extension faculty and Master Gardeners reply to queries within two business days, usually less. To ask a question, simply go to the OSU Extension website and type in a question and the county where you live. Here are some questions asked by other gardeners. What’s yours?

Spider webs reflect the setting sun along one of the many trails at Mary S. Young Park.Dania Maxwell/ Staff/2011

Q: We are very concerned about the lack of garden spiders in our landscape this year. We normally will see many mature spiders in their webs by fall, but we have seen none this year and wonder if this is due to the extreme heat in June or global warming in general. We found an article about the lack of garden spiders in Switzerland and it was said that the lack of garden spiders there was due to a 75% decline in flying insects. We are worried about what this means for our planet. Thank you in advance for your help in answering our concerns. Also, is there anything we can do to bring them back? – Multnomah County

A: Your question is very difficult for me to answer with confidence, because causation is one of the most difficult things to show in ecological studies. Nature is diverse, and there are likely many factors that act alone and in concert to influence a given group of animals.

It is true that several studies have shown an alarming decrease in insect abundance, biomass and/or diversity. However, even among these studies, the factors that are causing the decrease have been suggested but not confirmed. Among the potential factors suggested are climate change, agricultural intensification (e.g., pesticides, mono-cropping), and habitat loss. Agricultural intensification and pesticides seem to be a prime candidate for insect loss. Yet, scientists are still working to disentangle the impacts of things like poor nutrition (monocrops) from pesticide toxicity from habitat destruction.

All of this is to say that it seems to make perfect sense that spiders might decrease while insects (which are an important source of prey) are decreasing. But, I can’t definitively and confidently tell you, “Yes! This is what explains your observations.” Science can be frustrating, in that sense.

What can you do to help bring spiders back to your yard? First, thank you for asking. The fact that you are asking that question goes a long way to helping conserve spiders and other invertebrates. My quick list of actions you can take to help spiders includes:

  • Eliminate or reduce insecticide use in your garden. Doing so will directly and indirectly benefit spiders, by protecting them from pesticide harm and helping to ensure more prey for them to feed upon.
  • Dedicate one or more small areas of your garden as “no mow” or “no-till” areas. Many ground-dwelling spiders live beneath leaf litter mulch and other ground covers. Providing an area free from disturbance will help to protect them.
  • Add in structures for web-building spiders. Many studies have shown the web-building spiders are limited by a lack of places where they can build their webs. Moving your garden from the two dimensions of a lawn-dominated system to the three dimensions of a garden that has ground covers, perennials, shrub and trees has been shown to increase web-building spider abundance, and to help reduce insect pests in gardens. Some ecologists, when studying web-building spiders, have found that adding in artificial structures (like a tomato cage or two) can help bring more web-building spiders into a site.
  • Encourage your family and friends to be more tolerant of spiders. Many people hate spiders, and will seek to kill them on sight. If more folks knew about the benefits that spiders bring to the garden and to ecological systems, they might help you to conserve and protect them. – Gail Langellotto, OSU Extension entomologist

What’s the best way to reduce codling moth?

Q: Instead of pesticides, I’d like to try using a physical barrier or trap around the trunk of my apple tree to reduce codling moth. When/how should I do this and what are good materials to use? – Marion County

A: Trunk banding/trapping is used to catch the insects after they have left the fruit and are moving down to the ground to pupate. So, this wouldn’t protect your 2022 crop but could reduce the number of moths that could damage the summer 2023 fruit.

This publication from Colorado State University Extension has a great description.

Trunk banding involves purposefully providing areas for pupation, so that the insects can later be destroyed. Bands can be created by cutting strips of corrugated cardboard 1 1/2 to 2 inches wide and long enough to wrap around a branch. (Burlap, tied to the trunk, may also be used as a band.) Place the cardboard bands around branches at points where there is a transition from smooth to rough bark (Figures 10a and 10b). Place the corrugated face of band around branch and staple. As the codling moth larvae leave apples, they will crawl down the branch and move into the corrugated openings as a site for pupation. If there is loose bark on the fruit trees that can provide alternate places for pupation, the bark flaps should be removed.

During the growing season, bands should be checked frequently (every week or two) during periods that coincide with the end of a generation, the time when the full-grown larvae are moving to pupation sites. The larvae can be killed by crushing or removing and replacing bands. Larvae that are overwintering within the band can be removed any time after apples have been removed from the tree and before the emergence of adults the following spring. – Brooke Edmunds, OSU Extension Horticulturist

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