Orb-Weaver Spiders: A Primer

Members of the arachnid family, Araneidae, are known as orb-weavers because they construct flat, orb-shaped webs that vary in size from small to very large. These often-colorful spiders can commonly be found near or on buildings but rarely are located indoors except in places like garages, sheds or warehouses.

The most well known orb-weavers may well be the garden spiders due to their large size and the fact that they are active during the day. The golden silk orb- weaver is common along the Gulf Coast and is one of the larger United States spiders in terms of leg span. Spinybacked orb- weaver spiders (Figure 1) occur in four different color variations and occur in the Southeast. They are one of the more common orb-weavers seen around homes in Florida. Some species, like the furrow orb-weaver and longjawwed orb-weaver, are usually found in larger numbers on or near buildings located near bodies of water. Many orb-weavers are active mainly at night, such as some members of the genera Neoscona and Araneus with their presence noted only by their webs.

Orb-weavers, like most spiders, are highly beneficial and are present around buildings because insects that serve as their food are abundant. Conservation of orb-weavers should be encouraged among residential customers by moving species from near the home to the further reaches of the yard and landscaping. This is especially true for larger species such as garden, giant silk and spinybacked orb- weavers. Moving a few such spiders using a jar or cup takes little effort or time and is beneficial to the yard environment.

Where larger populations of orb- weavers (i.e., furrow orb-weavers), together with comb-foot spiders and similar web-builders, are found in webs constructed on buildings, several factors and strategies need to be considered.

BUILDING LOCATION. The first consideration is building location. Structures located next to fields, wooded lots or bodies of water will have much higher spider populations. Spiderlings are constantly bombarding buildings from fields and woodlots during warmer months, rapidly repopulating sites where control measures have been carried out. Little can be done to change these circumstances, but these facts do raise the importance and significance of implementing the following strategies.

The reason spider populations are high is that the house or building is supporting or attracting larger numbers of insects, in most cases due to exterior lighting. Simply changing exterior lights to yellow lamps (e.g., “bug light” bulbs or sodium vapor lamps) greatly reduces the numbers of nighttime insects, thus the numbers of spiders plummets due to lack of available food. Yellow bug light bulbs are available in LED form for standard fixtures. White LED bulbs used in residential and commercial fixtures do attract fewer flying insects than metal halide or incandescent lights, but still attract more insects than yellow-based lighting.

The complexity and fullness of landscape plantings next to and near buildings also increases the available insect food for higher spider populations. More sparse landscape plantings next to buildings is better for spider reduction than thick shrubbery and heavy ground- covering vegetation. Changing out landscaping can be expensive and impractical, but can be considered for the worst cases.

Exclusion efforts by use of screens on windows, doors and vents (attic and foundation) and sealing cracks and gaps in exterior walls is helpful in keeping out spiders, but will never be entirely successful at stopping all spider incursions.

For more orb-weaver spider photos from Stoy Hedges, visit Online Extras on PCTOnline.com.

WEB REMOVAL. Likely the best strategy for pest professionals is thorough regular web removal using cobweb brushes on telescoping poles. Removal of webs and egg sacs using brushes makes it easier to detect where spider activity is repeatedly established on a building on future services. This helps to target residual treatments where activity is likely to be the highest. Web removal provides immediate aesthetic benefits as customers see clean corners and soffits free of old and new webs. In severe cases of web-building spiders within garages, warehouses or other spaces, removal by vacuuming is worth the effort.

Observations on spider control on my own home showed best results if spiders were treated prior to removal by brushing. Spiders often drop to the ground if webs are disturbed and thus avoid being mortally injured by the brushing action. These spiders then climb back up walls and construct new webs. Treatment before brushing is best done with lighter fan spray applied via a 1-gallon or backpack sprayer. Higher volume applications using truck-mounted spray units will cause webs to mass and stick to walls and brick, thus preventing removal with a brush.

FINAL THOUGHTS. In summary, most web-building spiders on buildings will tend to be types other than orb-weaver spiders, but the techniques for management and control are the same for any web-building spiders. Larger orb-weavers, such as garden spiders, should be relocated to far reaches of the yard, where feasible. Making the building less attractive to insects that serve as spider food by changing lighting and/or landscaping is the best strategy for minimizing future spider populations.

The author is president of Stoy Pest Consulting, Eads, Tenn.