Spider Sunday: Orchard Orbweaver

People who think all spiders are creepy, and have no beauty about them whatsoever have never seen an Orchard Orbweaver, Leucauge venusta. This member of the family Tetragnathidae is pearly white or silvery with black, yellow, and red markings, and green legs. It is a truly lovely animal.

The Orchard Orbweaver is one of two species in the genus Leucauge found in North America north of Mexico. The other is L. argyra, found only in Florida. L. venusta occurs from southern Ontario, Canada to Florida, and east to Nebraska and eastern Texas. It also ranges as far south as Panama. I have encountered them in Ohio, Massachusetts, and South Carolina.

Despite its common name, it is not terribly common in orchards, preferring woodland habitats where it builds a horizontal orb web in shrubs, and bushes. Younger spiders have their webs closer to the ground, while adults spin them about 1.5 meters high. The web of an adult spans roughly twelve inches, and features an average of 30 radii (“spokes”) and more than sixty spirals.

The spider hangs upside down in the hub (center) of its snare, displaying a mostly black underside with a red crescent or rectangular spot. Unfortunately, many people mistake the Orchard Orbweaver for a black widow because of that red marking. However, widow spiders are almost never out in their webs during the day, and widows build tangled webs, not orbs.

It is also easy to mistake this species for orb weavers in the genus Mangora, but those spiders spin a vertical orb web, not a horizontal one. The Basilica Spider is also similar, and spins a horizontal orb web, but the orb is pulled into a dome shape. Finally, many sheetweb weavers in the family Linyphiidae resemble Leucauge venusta, but none of them spin orb webs.

Mature females of the Orchard Orbweaver measure 5.5-7.5 millimeters in body length, and males 3.5-4 millimeters. Individuals overwinter as sub-adults, hiding in leaf litter and under loose bark. Adults are found most abundantly in late spring and early summer, perhaps avoiding competition with other web-building spiders that mature later in the season.

The Orchard Orbweaver is shy, and drops from its web straight to the ground if it feels threatened, often disappearing into leaf litter and undergrowth. Don’t let that deter you from looking for it. These are highly photogenic spiders.

Sources: Gaddy, L.L. 2009. Spiders of the Carolinas. Duluth, MN: Kollath+Stensaas Publishing. 208 pp.
Jackman, John A. 1997. A Field Guide to Spiders & Scorpions of Texas. Houston: Gulf Publishing Co. 201 pp.
Jones, Janson. 2011. “Leucauge venusta (Orchard Orbweaver),” Dust Tracks on the Web
Weber, Larry. 2003. Spiders of the North Woods. Duluth, MN: Kollath+Stensaas Publishing. 205 pp.

Spider Sunday: Cave Orbweaver

One of the oddballs of the family Tetragnathidae is the Cave Orbweaver, Meta ovalis. It does not have the exaggerated jaws, long legs, or elongated body typical of most other long-jawed orb weavers. It even spins a vertical orb web, in contrast to the usual horizontal webs made by other tetragnathids.

Meta ovalis has also gone by the name Meta menardi, but it has been determined that M. menardi is a separate species found only in Europe and Asia (to Korea).

This is an average-sized spider for orb weavers, females measuring 8-10 millimeters in body length an males averaging 9.5 millimeters. The species ranges from southeast Canada to Georgia and west to the Mississippi River, especially along the Appalachian Mountains and the Ozark Plateau. It is one of two North American species in the genus, the other being found only in California.

The typical habitat for cave orb weavers is, surprise, surprise, caves, abandoned mines, old wells, basements, and densely-shaded ravines. That is why I found this specimen on the exterior of a building, in broad daylight, in New Hampshire, on October 11, 2009. Since it was not associated with an obvious orb web, my first thought was that it was a sheetweb weaver in the family Linyphiidae, or maybe a cobweb weaver in the family Theridiidae. The spiny legs ruled out cobweb weavers, but I was still mystified.

I collected the specimen and took it to the lab I was using at University of Massachusetts, Amherst, where I took the two images on the table. Fortunately, I had access to good references and was able to eventually identify it correctly.

This is not a true cave inhabitant in the sense that it dwells only in the entrances and twilight zones of caves, and not in the deep recesses. It has obvious eyes, and is fully pigmented. These characteristics classify it as a “troglophile” rather than a troglobite. The webs are usually built from the ceiling of a given location, especially in protected situations (termed “kettles” and “bells” on the ceiling of caves) where dessicating air currents can’t dry them to death. The spider seems to prefer sitting near the edge of the web rather than its center, but frankly, little research and observations have been done on cave orb weavers.

One exception to the dearth of studies is Meghan Rector’s thesis, cited below. She discovered that immature specimens of the cave orb weaver may be distributed slightly deeper in caves, and construct larger webs to increase the potential for the capture of more scarce prey.

Clearly, more work is needed just to determine the geographic range of this species. Fauna of caverns in general is poorly known, and often endemic to a single cave or cave system. Spelunking, anyone?

Sources: Slay, Michael E., Daniel W. Fong, and Mark D. Kottmyer. 2009. “Meta ovalis (Araneae: Tetragnathidae) observed preying on a troglobiotic milliped, Causeyella (Chordeumatida: Trichopetalidae),” Speleobiology Notes 1: 3-5.
Rector, Meghan Anne. 2009. “Foraging in the Cave Environment: The Ecology of the Cave Spider Meta ovalis (Araneae: Tetragnathidae). Master of Science Thesis. 113 pp.
Reeves, Will K., John B. Jensen, and James C. Ozier. 2000. “New faunal and fungal records from caves in Georgia, USA,” J. Cave Karst Stud. 62(3): 169-179.
Yoder, Jay A., Joshua B. Benoit, et al. 2009. “Entomopathogenic fungi carried by the cave orb weaver spider, Meta ovalis (Araneae, Tetragnathidae), with implications for mycoflora transfer to cave crickets,” J. Cave Karst Stud. 71(2): 116-120.

Spider Sunday: Longjawed Orb Weavers

The longjawed orb weavers in the family Tetragnathidae are among the most abundant of summertime spiders. Today I’ll focus on the genus Tetragnatha. There are fifteen species collectively distributed across the entire North American continent, and I’ll bet you can find at least one near you.

The tetragnathids get their common name from the fact that many species have extraordinarily long chelicerae (jaws) and fangs. Their entire bodies, and legs, are long for that matter. Their narrow shape and resting posture helps to camouflage them, even if they are sitting in the middle of their webs.

Longjawed orb weavers construct orb webs in a horizontal plane, or close to it. This helps differentiate them from the majority of orb weavers in the family Araneidae that create webs on a vertical axis. I find that longjawed orb weavers seem to fit in one of two categories: small species that live in meadows and fields; and larger species that make their webs over water. There is naturally some overlap, but meadows and riparian corridors are where you are most likely to encounter them.

They are tolerant of each other’s company, too, often building individual webs in close proximity to others of their kind. This behavior reaches its zenith in Tetragnatha guatemalensis.

That species is essentially social, and capable of spinning communal webs that can stretch for acres. Remember that enormous web in Lake Tawakoni State Park in Texas, back in 2007? That was the work of thousands of T. guatemalensis spiders. I found a similar situation, on a smaller scale, at Sweetwater Wetlands in Tucson, Arizona in late October of 2010 (see below). It is difficult to communicate the vast expanse of silk, but it certainly exceeded what tent caterpillars can do.

Those species that live in meadows usually occupy the hub of their webs, but their long bodies, complemented by long legs held close to together, disguise them as broken bits of grass stems. Many are straw-colored and they blend in quite well. When disturbed, they dash out of their webs to hug a grass stalk, merging almost imperceptibly with the plant.

Water-loving species usually sit on the perimeter of their webs, again hugging the substrate, often a twig or piece of emergent vegetation that anchors one corner of their web. The orbs usually have the spiral widely spaced. Still, the snare is very effective in trapping adults of aquatic insects like midges, gnats, and mayflies that emerge directly from the water into the air. The horizontal web intercepts them on the way up.

Mature tetragnathids, depending on the species, can measure from 5-16 mm or so in body length. The spindly legs make them seem even larger. Males are usually the (slightly) smaller gender. During mating, both sexes grasp each other’s jaws. Males may have spurs on the chelicerae to receive the female’s fangs, presumably to avoid fatal results from the whole affair.

Females lay their eggs in egg sacs, and those silken packages can vary in appearance by species. Some are adhered closely to a twig or other object, blending in with the substrate. Others, like the one above that I found in south Texas, are suspended on the periphery of the web. Once the web itself is long gone, the remaining egg sac can be a puzzling object for the naturalist to make sense of.

Identifying longjawed orb weavers to species is an inexact science based in large part on the genitalia; and also on the relative spacing of the eyes, and the length of the jaws relative to the length of the carapace (top of the cephalothorax). It is enough to simply appreciate their diversity in my own opinion. One species that is easy to recognize is the emerald green Tetragnatha viridis, found in the eastern U.S. and adjacent southern Canada. There is no mistaking it for any other.

See if you can spot some of these unique spiders near your home, or the next time you go down by the river or lake. You might also want to thank them for helping diminish the populations of midges, mosquitoes, and other insects that annoy you at this time of year.