Spider Sunday: Starbellied Orbweaver

There is no shortage of the weird in the spider world, and I found one more example on our trip to Cape May, New Jersey on October 3, 2012. A series of posts linked with nylon rope provides a barrier along the dunes in Cape May Point State Park, and this fence was being utilized by one of the strangest of North American spiders, the Starbellied Orb Weaver, Acanthepeira stellata.

One of my friends on Flickr asked “Why is it star’bellied’ when it's star-butted? Is there more star-ness on its belly?” I have to agree with her. Maybe the person that first saw one described it from the ventral side. The pointy tubercles certainly show up well from both angles. The spikes probably help deter potential predators. Indeed, the abdomen is not as soft as it is in many other spiders.

Acanthepeira stellata is one of four North American species in the genus, collectively found from southeastern Canada south and west to southern California. This species in particular is known from southeast Canada to Florida, and west to Kansas and Arizona.

These are not terribly large spiders. Mature females measure only 7-15 millimeters in body length, males 5-8 millimeters. The shape of the abdomen is distinctive, making them easy to identify in the field. Indeed, fields and meadows with tall grasses and herbs are where I have found them. Most references indicate they prefer this kind of habitat as well, where they lash their webs to rather flimsy stalks and leaves. They are also fairly common in cotton fields and other crops in the southern Great Plains.

Starbellied spiderlings emerge from egg sacs in summer, and overwinter as immature or penultimate (one molt removed from adulthood) specimens. Adult females may be found from May to October, at least in Illinois (Moulder, 1992). Mature males can be seen from May to September. I found adults, or near-adults, in Cape May, and the one pictured at the top of the page appears to be “ballooning.” Ballooning is a dispersal strategy used by many young spiders to travel afar and stake out their own territories. A spiderling typically climbs to a high point, stands on tip-toe (“tip tarsus?”), and issues long strands of silk from its abdomen. These threads are caught by the wind, and when the spider lets go, it may be blown hundreds of feet, if not a mile or more. They can gain serious altitude, too. One baby A. stellata was captured at 1000 feet in the air over Tallulah, Louisiana on December 13, 1930 (Fitch, 1963).

These are orb weavers, and they spin the characteristic round webs of other members of the family Araneidae. The webs span about 6-10 inches, and are rarely more than four feet off the ground. The spider usually sits in the center (hub) of the web, head down, awaiting the impact of a prey insect. When disturbed, the spider invariably drops to the ground and feigns death, legs tucked close to the body. Among leaf litter and tangled grasses, it can virtually disappear until danger passes.

The Black and Yellow Mud Dauber, Sceliphron caementarium, is known to prey on Starbellied Orbweavers, paralyzing victims and stashing them in mud cells as food for its larval offspring.

Acanthepeira stellata itself preys mostly on nymphs (immature) of grasshoppers, plus other medium-sized insects. There is one record of an adult female preying upon an American Green Tree Frog, Hyla cinerea, but this is certainly not a routine event (Lockley, 1990).

Sources: Fitch, Henry S. 1963. Spiders of the University of Kansas Natural History Reservation and Rockefeller Experimental Tract. Lawrence, KS: University of Kansas Museum of Natural History, Misc. Publ. no. 33. 202 pp.
Gaddy, L.L. 2009. Spiders of the Carolinas. Duluth, MN: Kollath+Stensaas Publishing. 208 pp.
Lockley, T.C. 1990. “Predation on the green treefrog by the star-bellied orb weaver, Acanthepeira stellata (Araneae: Araneidae),” J. Arachnol. 18(3): 359.
Moulder, Bennett. 1992. A Guide to the Common Spiders of Illinois. Springfield, IL: Illinois State Museum Popular Science Series, vol. X. 125 pp.
Weber, Larry. 2003. Spiders of the North Woods. Duluth, MN: Kollath+Stensaas Publishing. 205 pp.

Wasp Wednesday: Purslane Sawflies

Not all wasps sting, and not all feed on other insects in their youth. The larvae of sawflies are vegetarians, and many are mistaken for caterpillars. You need not venture far to find sawflies, either. I found the adult female specimen below in my own backyard on the evening of September 18. Through a little detective work I discovered she is a Purslane Sawfly, Schizocerella pilicornis, in the family Argidae.

This species is unique among all argids (worldwide) in that its larvae feed internally on the host plant, mining inside the leaves of purslane. Until recently, it was thought that some larvae of S. pilicornis feed externally. Analysis of mitochondrial DNA has demonstrated that those leaf-nibbling larvae belong to a separate species, S. lineata (Hartsough, et al., 2007).

Adult females can be distinguished by the amount of black markings on the top of the otherwise red (or orange) thorax. Females of S. pilicornis have a solid, or nearly solid, black stripe down the center of the thorax, constricted in the middle. Females of S. lineate have very reduced black markings along the midline of the thorax. S. lineate is also slightly larger, females averaging about 7 millimeters to the 5-6 millimeter length of female S. pilicornis.

Both species are widespread in the New World, ranging from southern Canada to at least Central America. S. pilicornis occurs at least as far south as Argentina. U.S. records for S. pilicornis include Arizona, California, Colorado, Connecticut, Washington, DC, Florida, Indiana, Iowa, Kansas, Maine, Maryland, Michigan, Minnesota, Mississippi, Nebraska, New Hampshire, New Jersey, Ohio, Oregon, Texas, Virginia, and Washington. The species may actually be adventives here, and native to South America. At least, it was not described from North America until 1900.

Life history information may be open to debate since it comes prior to the realization that two species are involved (Gorske, et al., 1977). Females lay one egg per leaf, inserting the ovum into the foliage with the saw-like ovipositor that gives sawflies their common name. Larvae feed for roughly six days, going through five instars (an instar is the interval between molts). Mature larvae tunnel into the soil to a depth of about 3.5 centimeters where they pupate. Adults emerge a week later (during the summer generations; otherwise they overwinter as pupae). Their lifespan as adults is apparently very short, only 24 hours according to one source (Gorske & Hopen, 1976).

There can be up to six or seven generations annually, at least in Illinois, where these insects exert a small degree of biological control against purslane.

Males in this genus are easily identified by the last antennal segment, which is forked. It looks like the insect has four antennae instead of the two it should have.

I have found numerous males, and this one female, “sleeping” out in the open on grasses and other vegetation at sunset. Many wasps (and solitary bees) can be found by looking in fields and meadows for sleeping individuals at dusk, in the early morning, or during inclement weather.

Sources: Gorske, S.F. and H.J. Hopen. 1976. “Purslane sawfly (Schizocerella pilicornis) as a biological control agent of Common Purslane (Portulaca oleracea L.),” a paper presented at the 73rd annual meeting of the American Society for Horticultural Science, August, 1976.
Gorske, S.F., H.J. Hopen, and R. Randell. 1977. “Bionomics of the Purslane Sawfly Schizocerella pilicornis,” Ann. Entomol. Soc. Am. 70(1): 104-106.
Hartsough, Chester D.B., Edward F. Connor, David R. Smith, and Greg S. Spicer. 2007. “Systematics of Two Feeding Morphs of Schizocerella pilicornis (Hymenoptera: Argidae) and Recognition of Two Species,” Ann. Entomol. Soc. Am. 100(3): 375-380.

Spider Sunday: A Common "Indoor" Spider

At this time of year, there is one spider that is commonly encountered indoors in the eastern United States and southeast Canada. It has a bi-colored body that makes it conspicuous and different from most other spiders one is likely to see around their residence. Trachelas tranquillus, is sometimes known as the “Broad-faced Sac Spider,” a member of the family Corinnidae.

This is a spider of average size, adult females measuring 7-10 millimeters in body length, males 5-6 millimeters. It occurs from Nova Scotia and Minnesota south to Kansas, Oklahoma, and northern Georgia, preferring deciduous woodlands. In nature, specimens are often found in retreats fashioned from curled leaves; or they are seen occasionally under stones.

I have seen this species hunting actively at night, prowling around porch lights where it may be hunting various insects attracted there. Trachelas does not spin a web, but does lay down draglines to help secure itself during climbs. Females probably also impregnate their draglines with pheromones (scents) so that males can track them down.

© Ken Lebo 2012

Mating usually happens in summer and early fall, after both genders have matured (nice images on the highlighted link). Females create a lens-shaped egg sac, the bottom flat against a substrate and the top slightly convex. The whole package is roughly ten millimeters long and usually attached beneath loose bark, or under a rock.

Besides killing live prey, Trachelas may scavenge on dead insects. Perhaps this is why it prospers when other spiders have either perished or gone into hiding in autumn. This scavenging habit may also influence the outcome in those rare instances when the spider bites a human. Secondary infections from its bite have been recorded, originally interpreted incorrectly as caused by the spider’s venom.

© Sarah Rose

The fact that Trachelas hunts regularly in and around homes and other buildings means it is more likely to have interaction with people. Still, verified cases of bites are infrequent, and usually result in only localized pain and swelling. People sensitive to arthropod venoms, or prone to allergic reactions, should seek medical attention for any arachnid bite (or sting in the case of scorpions).

Further complicating this picture is the confusion of Trachelas with another spider that is completely innocuous, though more intimidating. The Woodlouse Hunter, Dysdera crocata, is a specialized predator of woodlice, known commonly as “sowbugs,” “roly-polies,” or “pillbugs.” This species has exceptionally long jaws and fangs it uses to turn over its armored prey. While it looks dangerous, it is not.

Dysdera crocata © Nick Richter 2010

Dysdera is not native to North America, having been introduced from Europe at some point in our history. It has also become accustomed to prowling around human dwellings, so may be found indoors. It does not climb as well as Trachelas, however, and in my experience the Woodlouse Hunter prefers to hug baseboards.

Dysdera crocata © Sarah Rose

I encourage my readers to appreciate all spiders, but also act responsibly. It is a good idea to try and exclude spiders from entering your home and workplace by repairing worn weatherstripping on doors, mending holes in window screens, and sealing any cracks and crevices that could offer passage for insects and arachnids. Be careful when bringing objects indoors from outside, too, like firewood, gardening implements, children’s toys, and shoes and clothing left outdoors overnight.

Sources: Cox, Shelly. 2011. “Ground Sac Spider,” MoBugs blog.
Eaton, Eric R. and Amanda Howe. 2012. “Trachelas tranquillus (Ground Sac Spider),” Spiders.us.
Jacobs, Steve. 2002. ”Broad-faced Sac Spider,” Penn State University fact sheet.

Wasp Wednesday: Wasps in a Bubble

One of the strangest inquiries I have ever received was the image below, from a Facebook friend named James Adams. He took the picture at the Rio Santiago Nature Lodge near Santa Ana, Honduras (northern coast). Not familiar with the tropical fauna there, I forwarded the image to Dr. James Carpenter at the American Museum of Natural History in New York City. Dr. Carpenter is a world authority on social wasps with much experience in the neotropics.

© James Adams

Here is the original post to James Adams’ Facebook page:

”OK so this is one of the weirdest things I've seen in nature. These small, black wasps created a normal-looking nest amidst leaves of a soursop tree. Then either they, or some other creature, encased the entire thing in this "plastic" bubble. Great protection from the rain, but WTH ????? There's a little oval-shaped hole in the bottom so they can get in and out. Anyone like Court Whelan or Deborah Matthews know what these wasps are called? Crazy! Rio Santiago Nature Resort, Honduras —“

Dr. Carpenter wrote the following in response to my query:

"It's a nest made by a species of Protopolybia. There are several species in the Amazon that make envelopes of "wax paper," such as chartergoides - you may encounter descriptions in the literature under the generic name Pseudochartergus. The paper that paper wasps make is most commonly wood fiber bound with saliva - these critters have just left out the wood."

The other comments on the original Facebook post of this image were delightful. Piotr Naskrecki, an extremely experienced explorer in his own right, said “Absolutely amazing, I have never seen anything like this.” Holly Overmyer was jealous: “I wish I could make a little plastic bubble when I get caught in the rain.” John Afdem quipped: “I'm just guessing here, but perhaps its one of the Saranwrapipedes???” Kenneth Barnett, not to be outdone, replied “John, you must talking about Polyrapus opaqous?”

James Adams runs The Lodge at Pico Bonito, La Ceiba, Atlantida, Honduras. I just may have to visit both nature lodges to see this kind of phenomenon for myself.