The dense foliage of evergreens makes a perfect home for beneficial spiders such as the funnel web weaver, and a perfect food source for the spider-like spider mite. These arachnids can leave unsightly webs all over your ornamental conifers but only the spider mite threatens the life of your tree or shrub.
Funnel Web Weaver Description
Adult funnel weavers are brown spiders with two dark brown to black stripes on their heads and brown, black and white markings on their backs. They're medium to large spiders that run with quick, darting movements. Their spinnerets can easily be seen sticking out from the end of their abdomens.
Funnel Web Weaver Ecology
These spiders are commonly found in evergreens where they spin easily visible trampoline-like webs. At the back of each web is a funnel shaped tube where the spider hides while it waits for prey. As an insect walks across the web, vibrations alert the waiting spider. A funnel weaver's web is not sticky so the spider must sprint out to capture its meal. Aside from the hobo, spiders in the funnel web weaver family, Agelinidae, are not a danger to humans. They rarely leave their webs and eat many insect pests. Hobo spiders--which are rarely found above ground level--are brown, but lack the dark bands on their legs common in other Agelinidae spiders. They do have markings on their backs but these can be difficult to see without a hand lens. If the webs bother you, simply spray them with a hose to wash them from your tree or shrub.
They aren't true spiders but these arachnids do spin webs. You may see the webs and think you have an infestation of tiny spiders. Spider mites feed on the sap within leaves. As they feed, the leaves become mottled and bleached. Eventually they'll turn brown and drop off the plant. The fine webbing they spin coats leaves and twigs, capturing dirt, dust and debris. Severe infestations can cause the death of your evergreen.
Spider Mite Control
Healthy conifers are less susceptible to infestation. Keep your trees and shrubs appropriately watered and fertilised. Wash the plants with a strong jet of water weekly to kill adults and prevent eggs from being laid or from hatching. Only use pesticides on severely infected, small trees as improper use can aggravate a mite problem. Petroleum and summer horticultural oils are effective but can cause discolouration in blue spruce. Apply insecticidal soap in the spring after an egg hatch. Miticides containing dicofol are effective and are less toxic to mammals and beneficial insects.