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.

Flying Ants

I recently came across a male specimen of the "legionary ant" Neivamyrmex nigriscens while walking our dog in our Colorado Springs neighborhood. It was instantly recognizable to me, but it got me thinking about how most people would be hard-pressed to know what it was. Unfortunately, there are very few references for the identification of winged ants. This is a shame because it is often the "alates," males and winged queens, that are most obvious to the public.

Male Legionary Ant, Neivamyrmex nigrescens, Colorado

Indeed, worker legionary ants are mostly subterranean and nocturnal in their habits (nomadic, raid the nests of other ants to prey on the larvae and pupae), so hardly ever observed by the average person. Meanwhile, a homeowner may not notice he or she has an ant "problem" until the colony swarms, liberating a cloud of alates.

Alate queen carpenter ant, Camponotus sp., Colorado

Alates are typically larger than the worker caste of wingless, sterile females, so are more noticeable for that reason as well. In many cases, the winged reproductives resemble the workers in general appearance, but this is not always the case. The thorax of winged ants is frequently greatly expanded to accommodate the muscles that operate the wings, giving males in particular a distinctive "hump-backed" appearance.

Male carpenter ant, Camponotus sp., Massachusetts

Swarms are usually seasonal, and triggered by changes in day length, relative humidity, and air pressure, especially in the arid southwest U.S. where the onset of the monsoon rainy season sparks many ant species to swarm. These emergences can be spectacular events. Worker ants open new exits from nests in the soil, and scour the immediate vicinity to rout any potential predators and parasites.

Red Imported Fire Ant swarm, Solenopsis invicta, Georgia

Many swarm events take place in late afternoon, at dusk, after dark, or at dawn. Winged ants may be attracted to outdoor lights, which can lead to the assumption that the ants came from the house or building when that is not necessarily the case.

Colonies of a given species in a localized area swarm simultaneously such that members of different colonies can find each other and increase genetic diversity while decreasing the potential for inbreeding. Winds, and the insect's own muscle power, can take the ants far from their colony of origin.

Rough Harvester Ant swarm, Pogonomyrmex rugosus, Colorado

How do you know whether it is a winged ant or a winged termite? Please read my post on termite swarms for a concise explanation, and images of winged termites. Below is an image of a winged termite to compare to the ants illustrated here.

Alate dampwood termite, Zootermopsis laticeps, Arizona

What about wasp versus ant? That is a more problematic distinction, but most ants have distinctly "elbowed" antennae, whereas wasps often do not; or at least the first segment of the antenna is not as long as it is in ants. There are exceptions, of course, like the male Neivamyrmex ant shown at the top of this post that has no obvious elbow in the antennae.

Male Pavement Ant, Tetramorium sp., Colorado

Fortunately, I am not the only one who recognizes the need to pay more attention to alate ants in terms of research and public awareness. Laurel Hansen and Art Antonelli include a key to alates in their publication, listed below. Brendon Boudinot, in a guest post for Alex Wild's Myrmecos blog, extols the virtues of studying male ants for a clearer understanding of the phylogeny of the family Formicidae.

Alate queen thatching ant, Formica sp., Colorado

Sources: Boudinot, Brendon. 2013. "Male Ants Demystified," Myrmecos.Hansen, Laurel, and Art Antonelli. 2011. Identification and Habits of Key Ant Pests in the Pacific Northwest. A Pacific Northwest Extension Publication 624. Pullman, WA: Washington State University. 14 pp.
Houseman, Richard M. 2008. "Ants." University of Missouri Extension.

A Foreign Mud Dauber: Update

Back in the spring of this year, I broke the story of a new immigrant species to the U.S. that my wife found at the zoo where she works. The story is here, but today's post is the sequel. Initially, I thought that wasp might represent an isolated incident, a single specimen that managed to sneak over in a shipment to the zoo. That is clearly not the case now.

the Asian Sceliphron curvatum

Taking advantage of an unseasonably warm autumn afternoon on October 6, my wife and I went to Quail Lake Park here in Colorado Springs to look for birds and other wildlife. The park is in the foothills of the Front Range, not that far from the zoo. There, on the muddy shore of the artificial reservoir, in the dimming light of late afternoon, we saw a trio of wasps. Two were familiar natives: The Western Yellowjacket, Vespula pensylvanica, and the Black and Yellow Mud Dauber, Sceliphron caementarium.

Our native Sceliphron caementarium

Heidi asked if the third, smaller wasp was also a mud dauber, and I answered yes, pretty much dismissing it as simply an unusually dark S. caementarium. I took images, though, and looking at the result I was both excited and crushed. Here was another specimen of Sceliphron curvatum, and she was clearly gathering mud to make a nest. This is pretty conclusive evidence that this Asian species is now established here in the U.S.

Nearby the lakeshore is the restroom building for the park, and I wondered if this wasp had her nest there. Ironically, cliff swallows had built numerous nests under the roof over the "porch," but I could find no evidence of any insect nests, not even paper wasps. Some of the beams are hollow metal, though, and it is certainly conceivable that wasps are nesting out of sight.

S. curvatum about to take off with a ball of mud

I suspect that Sceliphron curvatum exists in other regions of the U.S., too, particularly around the Appalachian Mountains, but has simply been overlooked. It may not be abundant yet, but that can change quickly. When I lived in Cincinnati, Ohio, I recall finding my first specimens of the introduced European Paper Wasp (Polistes dominula) to be a novelty in the early- to mid-1990s. A few years later they were the second most common species of paper wasp I was seeing.

Again, I ask my readers to be on the lookout for this "new" mud dauber, and make your observations and images known through every means possible, especially social media like Facebook and Twitter where you are likely to get almost immediate confirmation or refutation of your identification. The more eyes looking out for unusual insects the better.

Return of "Arachtober!"

Like your favorite horror movie trilogy, sequel, or whatever, Flickr's group "Arachtober" returns with a vengeance(?) this month. It has become an annual treat for arachnophiles and macro photographers, but perhaps a cruel trick on arachnophobes.

Female Philodromus sp. guarding egg sac

This year's edition has special meaning for me because I have been contracted to write a new field guide to U.S. spiders for Princeton University Press. I am also responsible for furnishing images, despite having a small budget for image acquisition. Preceding authors of Princeton guides have set a high standard for image quality, and I feel an obligation to publish the best photos I can get my hands on.

Web of Labyrinth Spider, Metepeira sp.

Arachtober manages to recruit several new participants each year through word of mouth, blogs, and sheer curiosity. Not only spiders, but scorpions, ticks, mites, harvestmen, and all other arachnids are eligible for inclusion. The only hard and fast rule is that the image you post to the group must not have appeared on your own Flickr photostream previously.

Female Southern Black Widow, Latrodectus mactans

Overall, interest in spiders seems to be increasing among the general public. Judging by the many new groups that have been created on Facebook, turnouts at special exhibits like "Eight-legged Encounters," new blogs, and other indications, arachnids are achieving a much higher profile than ever before. This is great news, for there is still a great deal of work to be done to combat myth, superstition, misinformation, and fear.

Male jumping spider, Hentzia palmarum

Please consider contributing to "Arachtober" on Flickr, or find another way to dedicate some time to sharing your spider observations, questions, or images. There is much you can contribute to our collective knowledge by doing so.