Spider v. Spider: A case of predation by Cesonia bilineata (Araneae: Gnaphosidae) upon spiderlings of Pisaurina mira (Araneae: Pisauridae)?

When my wife and I were traveling in Georgia, we stayed at a bed and breakfast near Madison. The inn is situated on over 88 acres of farmland, forest, and river, and teems with wildlife from birds to insects. We spent the entire day of June 14, 2014 exploring the grounds. Along one forest edge I was fortunate to find a female nursery web spider, Pisaurina mira, guarding spiderlings. She was perhaps falling down on the job, though, as another spider appeared to have free run of the nursery web, feasting on spiderlings.

A female P. mira is a formidable creature. She can measure 12.5-16.5 millimeters in body length, with an impressive sprawling legspan. Her size alone would seem to be intimidating enough. No matter, apparently, to a female ground spider, Cesonia bilineata, which was present in the nursery web among shrubbery well off the ground. Adults of this spider are half the size of the nursery web spider, female C. bilineata being a mere 4.3-7.0 millimeters from front to back, and with much shorter legs.

I did not observe the ground spider in the act of feeding on the spiderlings, but she was more plump than usual. There were living spiderlings and shed exoskeletons from spiderling molts present in the nursery web.

Cesonia bilineata might make a habit of feeding on the spiderlings of other species, as one researcher observed the species in the nursery web of a Green Lynx Spider, Peucetia viridans, in South Carolina (Willey and Adler, 1989). So far the evidence for predation on spiderlings guarded by the mother spider is apparently "circumstantial," but intriguing and highly suggestive. C. bilineata is, in fact, known to prey on other spiders by attacking the victim from behind (Bradley, 2013)

Female Pisaurina mira guarding nursery web to right of image

I also find it curious that so many of the "ground spiders" are highly arboreal, more likely to be found clambering about on foliage and twigs, or scaling walls, than to se seen scurrying over the surface of the soil. They are incredibly agile, too.

Cesonia bilineata is a common, widespread spider in the eastern United States from New England south to the Florida panhandle and west to Nebraska. Look for it in wooded habitats.

Sources: Bradley, Richard A. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Willey, Marianne B. and Peter H. Adler. 1989. "Biology of Peucetia viridans (Araneae, Oxyopidae) in South Carolina, with Special Reference to Predation and Maternal Care," J. Arachnol. 17(3): 275-284.

Ground Spiders, Sergiolus

Few spiders are as colorful as those in the genus Sergiolus. Why they are so boldly marked is something of a mystery, though there is suspicion that they may be mimicking velvet ants, wingless wasps in the family Mutillidae that pack a potent sting. Sixteen species of Sergiolus are known north of Mexico.

Sergiolus sp. male from Indiana

These nomadic arachnids are very agile, at least when fleeing potential danger, and they often prowl through leaf litter, so you may only get a glimpse of one. Be patient, though, and it is likely to reappear. They are also good climbers, so don’t be surprised to find them on foliage, or walls, too.

Sergiolus are medium-sized members of the family Gnaphosidae, females ranging from 6-10 millimeters in body length, males 5.5 to 7 millimeters. They are mostly diurnal (day-active), so are even more conspicuous than the average spider. The obvious, cylindrical spinnerets at the tip of the abdomen are characteristic of all Gnaphosidae, but helps distinguish Sergiolus from colorful spiders in other families. There are other ornate gnaphosids, such as Callilepis, and separating the different genera hinges on subtle distinctions in the genitalia (epigynum of females, pedipalps of males).

Male Sergiolus sp. from Colorado

Since there are several species, I am reluctant to assign specific names to the images shown here. One of the more abundant species found from the Nebraska and Oklahoma eastward is S. capulatus, sometimes known as the Variegated Spider. It bears an uncanny resemblance to velvet ants in the genus Timulla, which frequent similar habitats: sun-dappled patches on the floor of deciduous forests. The spider is also found in gardens, meadows, even lawns.

Female Timulla sp. velvet ant

One common western species is S. montanus.

While Sergiolus does not spin webs to snare prey, they do construct retreats in which to molt, guard an egg sac in the case of females, and perhaps to overwinter. They probably live over a year, as adults can be found in almost any season. Obviously, they are most active during the warmer months.

Look for these and other spiders, as well as insects, in sunlit spots in wooded areas. You will be surprised at what shows up if you simply sit and watch. Sergiolus can also be found under stones and other objects in reasonably dry situations.

Male Sergiolus capulatus? from Indiana

You can keep gnaphosids in captivity with relative ease. Almost any container will do. Provide them with water, as they do not obtain water from prey. I furnish a small wad of cotton soaked in water at least once per week. A small insect can be fed to a spider every other week or so. Spiders are built to withstand surprisingly long periods without food. Remove the prey insect if it has not been consumed within two days. Spiders preparing to molt will not feed and are therefore vulnerable themselves to predation.

Note: Several members of the genus Sergiolus were once placed in the genus Poecilochroa, and older references treat them as such.

Sergiolus montanus? from Colorado

Sources: Bradley, Richard L. 2013. Common Spiders of North America. Berkeley: University of California Press. 271 pp.
Kaston, B.J. 1978. How to Know the Spiders (Third Edition). Dubuque, IA: Wm. C. Brown Company Publishers. 272 pp.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2003. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

Spider Sunday: Eastern Parson Spider

One of the more common and distinctive members of the family Gnaphosidae is the Eastern Parson Spider, Herpyllus ecclesiasticus. It gets its common name from the black and white color pattern that is reminiscent of the garb worn by old-time clergymen. It also sometimes makes house calls, which can be disconcerting to homeowners.

This species prowls mostly at night, and I find it fairly commonly around buildings, hoping to prey on small insects attracted to outdoor lights. It climbs well, so can be seen well off the ground.

By day, it hides under loose bark, or stones, boards, and other debris on the ground. Specimens that enter homes at night may seek refuge in clothing, shoes, and other objects. The spider may bite if trapped, but the effect of a bite depends mostly on the victim’s immune response. Rarely do symptoms exceed mild inflammation.

This is a mid-size spider, females ranging from 6.5-13 millimeters in body length. Males are 4.5-6.5 millimeters. The spinnerets are prominent in both genders, a characteristic of the family Gnaphosidae. Each spinneret is like a showerhead, with many tiny orifices through which silk is extruded.

The Eastern Parson Spider is widespread everywhere east of the Rocky Mountains, from southern Alberta across to Nova Scotia and south to Texas and Florida. West of the Rockies it is replaced by the Western Parson Spider, Herpyllus propinquus. Look for it in deciduous woodlands.

Mature specimens of this spider can be found year-round, suggesting it is fairly long-lived. Mated females spin an egg sac in autumn. The case is flat, and deposited in a silken retreat where the mother guards it. One egg sac in Connecticut, found under loose bark, contained 130 spiderlings.

Sources and Links: Aitchison, C.W. 1984. “Low-temperature Feeding by Winter-active Spiders,” J. Arachnol. 12: 297-305.
Cox, Shelly. 2011. “Eastern Parson’s Spider,” MObugs
Edwards, Robert L. and Eric H. 1997. “Behavior and Niche Selection by Mailbox Spiders,” J. Arachnol. 25: 20-30
Guarisco, Hank. 2007. “Checklist of Kansas Ground Spiders,” Kansas School Naturalist 55: 16 pp.
Minerva Webworks, LLC. 2012. “Eastern Parson Spider,” Sutton, Massachusetts, suttonmass.org.