Matthew Sarver » South Carolina

Southern Spiders #2: The Green Lynx

Matthew Sarver — Sun, 13 Sep 2009 04:43:11 +0000

Green Lynx Spider (Peucetia viridans)
Family: Oxyopidae

Lynx spiders (family Oxyopidae) are some of my favorites. They’re big, charismatic, and colorful. The family is a distinctive one with only 3 genera and 18 species in North America. Lynx spiders have prominent, long, straight spines on the legs, and a characteristic hexagonal arrangement of the eyes (which is somewhat visible in the second image below).

During my recent South Carolina field work, I frequently found the Green Lynx Spider (common throughout the south) on vegetation in open pine savannas and meadows. These sit-and-wait predators do not spin a web, but use their long forelegs to capture prey items.

Late summer is the mating season for these spiders. Females build egg sacs, which they attach to the plant substrate, sometimes protecting the egg sac by constructing a tied-leaf shelter around it (Willey & Adler 1989). Some, but not all, females guard the egg sac against predation until the young emerge (about 2 weeks). Spiderlings emerge from the egg sacs in autumn and overwinter as early instars, before reaching maturity the following season (at around 300 days).

Lynx Spiders feed on both herbivorous insects and pollinating insects, so the benefit to a flowering plant of hosting the spider is unclear, with reductions in herbivory potentially offset by reductions in pollination and fruit set. Some species of Peucetia in the neotropics live and forage exclusively on plants that bear glandular trichomes. Studies indicate that when prey is scarce, the spiders eat dead insects that adhere to the sticky trichomes. The presence of the spider reduces rates of herbivory on the host plant without having a significant impact on pollination (Romero et al. 2008). Thus, the relationship is thought to be a facultative mutualism. Studies of the Green Lynx Spider, however, indicate that Hymenoptera and Diptera (potential pollinators) are the most frequently consumed prey items (Randall 1982, Willey & Adler 1989), and that the spiders often forage on plant blossoms, so this species may not improve fitness of its host plant. Indeed, my observations of the species in the field have been primarily on blossoms, where it might be expected that pollinating flies and wasps would be the chief prey.

References Cited:

Randall, J.B. 1982. Prey Records of the Green Lynx Spider, Peucetia viridans (Hentz) (Araneae, Oxyopidae). Journal of Arachnology 10(1): 19-22.

Romero, G.Q., J.C. Souza, and J. Vasconcellos-Neto. 2008. Anti-herbivore protection by mutualistic spiders and the role of plant glandular trichomes. Ecology 89(11): 3105-3115.

Willey, M.B. and P.H. Adler. 1989. Biology of Peucetia viridans (Araneae, Oxyopidae) in South Carolina, with Special Reference to Predation and Maternal Care. Journal of Arachnology 17(3): 275-284.

Southern Spiders #1

Matthew Sarver — Wed, 19 Aug 2009 03:56:06 +0000

I don’t know about you, but I love spiders. While here in South Carolina, I was lucky to find and photograph several common and attractive species. This is the first installment in a series of posts in which I’ll highlight these species for the enjoyment of all of you arachnophiles out there!

Lined Orbweaver, Mangora gibberosa
Family: Araneidae

The Lined Orbweaver is a common spider that is widespread throughout the eastern United States. In the southeast, it is especially abundant in grassy pond pine (Pinus serotina) savannas like the one shown below.

Strung among the grasses throughout the savanna are small, white, silken rings that are conspicuously evident against the sea of yellowish-green vegetation. Upon closer examination, the white ring is at the center of a larger orb-web, the rest of which is invisible from a distance. The white part of the web is called the stabilimentum, a structure found in the webs of many species of orb-weavers (Araneidae).

The purpose of the stabilimentum has been debated among arachnologists for a long time. Hypotheses range from prey attraction to camoflauge for protection from predators to warning signals that keep megafauna from accidentally destroying webs. Phylogenetic work suggests that web-decoration with stabilimenta evolved several different times in many araneid lineages (Scharff & Coddington 1997).

My personal observations of the Lined Orb-weaver indicate that, in this species, one use of the stabilimentum is as a refuge from potential predators. When the web is approached closely or bumped, the spider quickly runs to the opposite side of the web from the intruder and hides behind the stabilimentum, which is sized perfectly to conceal the body of the spider.

How well this works, however, is open to debate. Bruce et al. (2005) tested the visibility of stabilmentum silk to birds and bees. They found that in one of their study species, the chromatic contrast between the spider and the silk was significant enough that the stabilmentum probably provided inefficient camoflauge from avian predators at close range. It’s also possible that, since they are visible to bees and other insects, the small, discoid stabilimenta of the Lined Orb-weaver may attract prey to the web by mimicking flowers.

Whatever their adaptive significance, the sight of dozens of these small, silken rings dotting the vegetation is a fantastic experience for the naturalist willing to look closely. The spider responsible for the web is pretty cool-looking as well!

For a nice review of the literature on this topic, check out Matt Bruce’s web site on web decorations.

Citations:

Bruce, M.J., Heiling, A.M., Herberstein, M.E. 2005. Spider signals: are web decorations visible to birds and bees? Biology Letters 1: 299-302.

Scharff N, Coddington J.A. 1997. A phylogenetic analysis of the orb-weaving spider family Araneidae (Arachnida, Araneae). Zool. J. Linn. Soc. 120: 355–424.

Spoonbill Mania

Matthew Sarver — Fri, 14 Aug 2009 05:07:15 +0000

The rash of unexpected Roseate Spoonbill sightings this summer has been a treat for birders up and down the east coast. While northward movement of juveniles during post-breeding dispersal is known for the species, the numbers of birds involved and the extent of the northward movement this season is impressive.

According to the Birds of North America species account, spoonbills, “especially immatures, occasionally disperse great distances, but seasonal patterns of movement are poorly understood” (Dumas 2000). In past years, the occasional individual has appeared as far north as Pennsylvania, Ohio, Wisconsin, and Nebraska. Spoonbills regularly disperse in small numbers along the gulf coast in the states of Alabama and Mississippi, and north along the Atlantic coast to Georgia. In 1972, a large movement of immatures occurred as far inland as Tennessee. This summer, spoonbills have appeared in many eastern states, including Virginia, Delaware, and New Jersey. In fact, I saw the bird that appeared at Thousand Acre Marsh in Delaware last month.

I’ve been fortunate to be in the Low Country of South Carolina for a couple of weeks, which is where I took the photo below. These birds were part of a larger flock that contained at least 47 individuals. The peak number of Spoonbills observed at this site this summer was 63 a few weeks ago.

I’m sitting in a john boat, taking this photo with a point-and-shoot camera, which gives an idea of how close I am to these birds. They don’t seem too bothered, do they? I keep wondering what drives these irruptions, and whether climate change is a contributing factor. Spoonbill foraging is dependent on fluctuating water depths, so water level changes at foraging habitat in Florida might trigger large-scale movements. Hopefully this year’s irruption (and its documentation by birders) will help us better understand the movements of this fascinating species.

Citation:

Dumas, Jeannette V. 2000. Roseate Spoonbill (Platalea ajaja), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/490