[Tech Talk]

Among the spiders that pest management professionals encounter regularly in the continental United States — especially in the South — are the longjawed orbweavers (Family Tetragnathidae). Despite the (not always obvious) anatomical similarities that spiders of this family share, such as enlarged jaws (chelicerae) edged with prominent teeth and the presence of a colulus (a tiny stub just in front of the spinnerets), the few species that we find associated with human structures look deceptively different. Let’s take a look at some representative longjawed orbweavers that you and your clients will find, sometimes in abundance, on and near buildings.

GOLDEN SILK ORBWEAVER. The golden silk orbweaver/spider, Nephila clavipes (see Figure 1 above), is the largest and most impressive of the longjawed orbweavers in our part of the world. Although spider systematists have assigned Nephila spiders to a separate family — the Nephilidae — most existing spider references include it in the Tetragnathidae. The female of this species actually looks more like one of the large garden spiders (Family Araneidae) than it does one of its closer relatives. The female’s silvery-white, gold and black body may attain a length of 1 inch or more and the leg span may reach 3 to 4 inches.

A very noticeable feature of this spider is its fuzzy "knees." The orb-shaped web is huge — often spanning several feet from tree to tree or from tree to building. The silk is a unique golden color. Males are much smaller than females and they typically hang out at the periphery of the female’s web, with her "permission," of course.

The sheer size of these spiders and their webs usually elicit a fright response in those who run into them unexpectedly. Bites (resulting from accidental encounters or childhood curiosity) are rare and may be painful but are not considered to be dangerous, except in cases of particular allergies to the venom or where bacterial infections ensue. Golden silk spiders mainly inhabit the Southeast but they occasionally hitchhike in/on vehicles to the Northern and Midwestern states, where they can survive until freezing temperatures prevail.

MABEL ORCHARD ORBWEAVER. The mabel orchard orbweaver or orchard spider (see Figure 2 on page 106), Leucauge venusta (previously Leucauge mabelae), is easily recognized by its elongate silvery-white abdomen marked with black, yellow and orange, and its translucent green and black legs. The orb-like portion of the web is not always apparent but the webs typically are steeply angled from one anchoring point to the other. The adult female body is ¹⁄³ inch long and males are noticeably smaller.

This spider is not considered to be dangerous if an accidental bite occurs. Mabel orchard orbweavers and their webs may occur sporadically among trees, shrubs and tall vegetation, especially in the northern part of their range (which is the eastern U.S. and California), or they may be densely spaced on branches and open structures. The latter condition may be observed on/in porticos, screened enclosures of patios, barns, loading docks and bridge truss work in the Southeast, where smaller flying insects abound.

GUATEMALAN LONGJAWED ORBWEAVER. The Guatemalan longjawed orbweaver, Tetragnatha guatemalensis, is a mainly silvery-white and brown spider having an adult body length of about ½ inch. Like the 15 other Tetragnatha species found in North America north of Mexico, T. guatemalensis has a slender, elongate body and legs, and it rests with the first and second pairs of legs held together directly in front of the body and the third and fourth pairs of legs held together directly behind the body. The resulting effect is that these spiders appear twig-like as they hang from their webs or elude detection on leaves and bark, much like stick insects (Order Phasmatodea). Adult males are close in size to the females but tend to be darker and have a very slender abdomen; also, typical of most male spiders, the pedipalps sport bulbs (used during mating) at their tips.

Despite the large, nasty-looking jaws apparent on both sexes, this is not an aggressive or dangerous species. Bites resulting from physical encounters and in self-defense may be similar to bee stings.

Although pest management professionals may encounter other Tetragnatha longjawed orbweaver species occurring on clients’ properties, T. guatemalensis arguably will make the biggest impression within its U.S. range, which includes the East, Southeast, Southwest and portions of the Midwest. It is the newsmaker of the genus: Individuals of this species appear to coexist nicely in close proximity wherever prey is abundant (e.g., close to bodies of water, including rivers and creeks). As a result, females and males have been known to spin their large webs so close together in some settings that they blend indistinguishably with one another, forming huge sheets of webbing. The resulting communal webs (often created in conjunction with other compatible spider species) have merited the attention of researchers and media alike. For example, countless individuals of T. guatemalensis contributed to the amazing web-enshrouded tree canopies documented in Lake Tawakoni State Park, near Wills Point in Hunt County, Texas, in 2007 (ScienceDaily, September 13, 2007). Also, T. guatemalensis is one of several spider species that contributed to the massive communal webs that covered the columns and roof trusses of the Back River Wastewater Treatment Plant in Baltimore, Md., until their removal in late 2009 (Greene et al, 2010).

When longjawed orbweavers and other web-building spiders create problems for clients in and on structures, the quickest way to alleviate the problem is to employ a strategic combination of extension handle web-removing tools and pest vacuums or shop vacs. These are especially useful when unsightly infestations occur on structures that overhang or border on fresh water systems.

References

Greene, A., J.A. Coddington, N.L. Breisch, D.M. De Roche, and B.B. Pagac Jr. 2010. An immense concentration of orb-weaving spiders with communal webbing in a man-made structural habitat. American Entomologist 56(3):146-156.

ScienceDaily, September 13, 2007, reprinted and adapted from material provided by Texas A&M University. http://www.sciencedaily.com/releases/2007/09/070912145919.htm

Dr. Gerry Wegner, BCE, is technical director and staff entomologist of Varment Guard Environmental Services and ProGuard Commercial Pest Solutions, Columbus, Ohio, and a member of the Copesan Technical Committee. E-mail him at gwegner@giemedia.com.

Copesan is an alliance of pest management companies with locations throughout North America. To learn more, visit www.copesan.com.