Spider Sunday: Cat-faced Spider

Here in the western United States, one of the most common orb weavers is the Cat-faced Spider, Araneus gemmoides. I do not find them to be that conspicuous, however, because the spiders hide in their retreats by day, emerging only at night to sit in the hub of their spiral snares.

This species is known in parts of Canada as the “Jewel Spider,” but its more common name of “Cat-faced Spider” is more descriptive. Araneus gemmoides is one of the angulate orb weavers that often sport a pair of conical humps near the front of the top of the abdomen. These “horns” mark the “ears” of the cat face, with variable markings on the abdomen reinforcing the feline moniker.

One variation, the “Cheshire Cat-faced Spider,” has only a smiley-face….Ok, I’m making things up now, but the pattern of markings is highly variable in this species. One reasonably consistent mark is a short, white vertical stripe on the front edge of the abdomen, usually crossed by two white chevrons.

Mature females are large spiders, especially when gravid, their abdomen full of eggs. They vary in body length from 13-25 mm. Males, in contrast, are a mere 5-8 mm as adults.

Cat-faced Spiders spin rather small webs in proportion to their body size, the prey-catching zone spanning maybe one foot or so, even if the foundation lines of the snare may stretch several feet between anchor points. The occupant invariably sequesters herself in a curled leaf or other retreat by day, sometimes still monitoring the web via a signal line running from her retreat to the hub.

As darkness falls, the spider emerges to repair its web, or simply spin a new one, after which she may settle in the center of the web, head down, to await potential prey.

In optimal situations, several individual spiders may spin their webs in close proximity. My friend Margarethe Brummermann showed me a small group of these spiders that occupied a cliff face in Peppersauce Canyon on the north side of the Santa Catalina Mountains in southern Arizona. Much attention is paid to the fact that A. gemmoides will spin its webs on or about homes and other buildings, but they are likely taking advantage of outdoor lighting that attracts large numbers of insects within range of their webs.

Females apparently spin only one egg sac in late autumn. The spiderlings emerge the following spring and disperse. Young spiders have exaggerated humps on their abdomen, like the one shown below. Perhaps they have to “grow into them.”

The Cat-faced Spider ranges from British Columbia and Saskatchewan east to Michigan and south through the Dakotas, Rocky Mountains, and Pacific states to Arizona. Look for mature individuals in late summer and throughout the fall.

It's 'Hopper Time!

Among the last insects to be seen or heard before the hard frosts of late autumn are grasshoppers. Diversity of the short-horned grasshoppers in the family Acrididae is especially great in the desert southwest and the Great Plains. Here in central Colorado, we have plenty of representatives from both of those areas, convening here on the Front Range.

I have only been here since October third, and I’ve already tallied 25 species, thanks to help from David J. Ferguson via Bugguide.net. Here is the list:

White-whiskered Grasshopper, Ageneotettix deorum

Western Spotted-wing Grasshopper, Cordillacris occipitalis

Velvet-striped Grasshopper, Eritettix simplex

Two-striped Mermiria, Mermiria bivittata

Wyoming Toothpick Grasshopper, Paropomala wyomingensis

Brown-spotted Range Grasshopper, Psoloessa delicatula

Speckle-winged Rangeland Grasshopper, Arphia conspersa

Northwestern Red-winged Grasshopper, Arphia pseudonietana

Clear-winged Grasshopper, Camnula pellucida

Northern Green-striped Grasshopper, Chortophaga viridifasciata

Wrangler Grasshopper, Circotettix rabula

Hayden’s Grasshopper, Derotmema haydeni

Carolina Grasshopper, Dissosteira carolina

Dusky Grasshopper, Encoptolophus costalis

Platt Range Grasshopper, Mestobregma plattei

Mottled Sand Grasshopper, Spharagemon collare

Finned Grasshopper, Trachyrhachys aspera

Kiowa Rangeland Grasshopper, Trachyrhachys kiowa

Pallid-winged Grasshopper, Trimerotropis pallidipennis

Red-shanked Grasshopper, Xanthippus corallipes

Two-striped Grasshopper, Melanoplus bivittatus (top of post)

Differential Grasshopper, Melanoplus differentialis

Gladston’s Spurthroated Grasshopper, Melanoplus gladstoni (above)

Lakin’s Grasshopper, Melanoplus lakinus

Migratory Grasshopper, Melanoplus sanguinipes

Most of the above were found as adults, sometimes with tattered wings or an absent leg or two. Some are nymphs at this time of year that will overwinter and become adults next spring. These includes the Velvet-striped Grasshopper, Brown-spotted Range Grasshopper, Speckle-winged Rangeland Grasshopper, Northern Green-striped Grasshopper (below), and Red-shanked Grasshopper.

Here in Colorado Springs, I’ve encountered 20 species. Different habitats, elevations, and micro-climates have their own unique fauna. The Two-striped Mermiria (below), for example, was found along the Arkansas River in Cañon City. These large slant-faced grasshoppers are more fond of riparian corridors with tall, thick grass.

Hayden’s Grasshopper and the Wyoming Toothpick Grasshopper were both seen in very short grass at Fountain Creek Regional Park, in a field just in front of the nature center.

At higher elevations, one can find the Wrangler Grasshopper, Circotettix rabula. These insects can sustain their noisy flights for many seconds, in contrast to most other grasshoppers. They frequent steep slopes with scree (broken rock fragments), however, so it is a dangerous challenge to get images of them. The image below came from Emerald Valley back in July, when I could shoot from a trail above the insect.

The cooler temperatures of autumn mean that grasshoppers struggle to keep warm. Many of them adopt "basking" postures like the Carolina grasshopper pictured below. The insect literally leans back to expose one side of its body fully to the sun. It even lowers its hind leg so as not to block heat from reaching its abdomen.

You can find images of most of the above species in my “grasshoppers” set on Flickr.com. I’m already looking forward to next spring, when some of the nymphs will be large, colorful adult insects. I’ll bring you the results then, too.

Wasp Wednesday: Western Paper Wasp

Here in central Colorado we are experiencing higher-than-normal autumn temperatures. Several record highs were broken Monday, October 24, 2011 in fact. The warmth has meant that most of the social wasps are still active. Among the most common of those is the Western Paper Wasp, Mischocyttarus flavitarsis. This insect can easily be mistaken for a species of Polistes, but Mischocyttarus has a petiolate (stalked) abdomen in contrast to the more sessile abdomen of Polistes.

Mischocyttarus is a genus of roughly 260 species that is most diverse in the neotropics of Central and South America. Their classification has presented something of a nightmare to entomologists and it seems the end is nowhere in sight. Currently, there are three recognized species that make into the United States and southwest Canada, all in the subgenus Phi. Here in the western U.S., only M. flavitarsis occurs, but it ranges from British Columbia to Mexico, east to Nebraska and west Texas. I have encountered the subspecies M. f. navajo in Arizona (see image below), which is also found in Mexico.

This genus constructs small, uncovered paper combs essentially identical to the nests of Polistes paper wasps. My personal observations of M. flavitarsis flavitarsis in Portland, Oregon have demonstrated that the wasps prefer to nest in cavities. This may be in response to the rainy climate there, and/or offer greater protection from birds. Avian predation is a chief mortality factor for larvae and pupae of other species in the genus (Hermann & Chao, 1984). Certainly, nests I have found elsewhere have been more exposed, such as the M. mexicanus mexicanus nest imaged below at Resaca de la Palma State Park near Brownsville, Texas.

Like other paper wasps, Mischocyttarus females prey primarily on caterpillars to take back to the nest and feed their larval siblings. A study of M. flavitarsis demonstrated that the wasps rely mostly on olfactory cues for detecting prey. They may home in on volatile chemicals secreted by plants in the wake of damage from caterpillars, and especially the odor of the droppings or “frass” left behind by feeding caterpillars (McPheron & Mills, 2007).

The adult wasps themselves frequently seek out colonies of aphids to sip the sugary “honeydew” secreted as a waste product by the aphids. You may find an abundance of wasps, flies, and other insects around deciduous trees, and even pine trees that are infested with aphids.

Male behavior is geared to finding mates. A study of M. flavitarsis navajo in Arizona revealed that in late summer, males “patrol” areas frequented by females. Riparian corridors are a typical location for this activity. Each male will stop frequently to scent-mark twigs, foliage, and other objects with a chemical secreted by his abdomen. The male vigorously defends his marked patches from competing males.

Males that emerge in the fall form leks near potential hibernation sites. A lek is a stage where males congregate to show off to females. In this instance, each male simply scent-marks a perimeter roughly ten centimeters in diameter and sticks to this territory. Incoming females are free to choose (or reject) any male without interference from other males.

At this time of year, females of Mischocyttarus are seeking places to hibernate. Males may seek shelter as well, but they are unlikely to survive until the following spring. The females may spend the colder months under rocks, logs, under loose bark on trees, in the attics of homes, or other protected niches. They can congregate peacefully with others of their kind, and even with Polistes paper wasps. Warm winter days may find the wasps emerging to bask and explore their immediate surroundings.

Mischocyttarus is one of many social wasps that can be observed even at fairly close range without interfering with their behavior or eliciting an attack response. Take time to get to know them. You might learn something that nobody else has yet seen.

Sources: Hermann, Henry R. and Jung-Tai Chao. 1984. “Nesting biology and defensive behavior of Mischocyttarus (Monocyttarus) mexicanus cubicula (Vespidae, Polistinae),” Psyche 91: 51-66.
McPheron, Linda J. and Nick J. Mills. 2007. “Influence of visual and olfactory cues on the foraging behavior of the paper wasp Mischocyttarus flavitarsis (Hymenoptera: Vespidae),” Entomol Gener 30(2): 105-118.
Preston-Mafham, Rod and Ken. 1993. The Encyclopedia of Land Invertebrate Behavior. Cambridge, Massachusetts: The MIT Press. 320 pp.
Silveira, Orlando Tobias. 2008. “Phylogeny of wasps of the genus Mischocyttarus de Saussure (Hymenoptera, Vespidae, Polistinae),” Rev. Bras. Entomol. 52(4).

Spider Sunday: Banded Argiope

In my three weeks as a new resident of Colorado Springs, I haven’t seen that many spiders, let alone orb weavers. I look up for the webs, but sometimes forget to look down. Some of our most spectacular orb weavers, in the genus Argiope, usually build their spiral snares close to the ground amid tangled weeds and other vegetation. It was by chance and the angle of sunlight that I spotted the webs of two Banded Argiope spiders, Argiope trifasciata, yesterday.

This spider is common over the entire United States, and warmer regions of the globe, though it is reportedly rare in southern Europe. Here in North America, adult specimens can be found deep into autumn. According to a fact sheet on this species from Penn State University, A. trifasciata has a strategy for enduring the cooler fall temperatures: The spiders orient their webs east to west, with the animal itself hanging head down in the center of the web. The ventral surface of the spider’s body, largely black in color (see the image below),

faces south, catching the sun’s warming rays. Studies also indicate that these orb weavers could easily overheat during the late summer (Tolbert, 1979; Ramirez, et al, 2003), so the webs are then oriented to reduce the spider’s exposure to full sun. The spiders even “obelisk” to a degree, tilting their abdomen away from the web surface to minimize or maximize exposure to the sun. The dorsal surface of this species is highly reflective, mostly silver in color with darker bands across the abdomen. Specimens vary considerably in the degree of banding, and just how dark those bands can be. Additionally, an inverted trident pattern is often visible on the top of the abdomen, the “tines” directed toward the rear of the arachnid.

The females are large arachnids, mature specimens ranging in body length from 15-25 millimeters. Males, on the other hand, are petite, only 4-5.5 millimeters.

This species often occurs in habitats frequented by its cousin, the Black and Yellow Argiope, A. aurantia. The two spiders do look essentially identical on the underside, but note that the legs of the Banded Argiope are annulated, whereas the extremities of the Black and Yellow Argiope are reddish brown basally and mostly black distally. The abdomen of the Banded Argiope is also quite pointed in contrast to the more broadly oval, blunt-ended abdomen of the Black and Yellow Argiope.

Females fashion an egg sac shaped like a kettledrum, flat on the upper surface and highly convex otherwise. The tough, papery silk on the exterior of the egg sac helps camouflage the package amid the dry, dead autumn weeds.

I find this spider to be strikingly beautiful. I can still recall the first one I saw as a child in Portland, Oregon. She had her web amid an ornamental, low-growing juniper along the steps to our front door. I could visit her every day once I knew where to look. My friend and mentor, naturalist Jim Anderson, was the one who helped me identify her as I remember.

Such can be the positive power of nature’s cryptic beauty if you are not prone to arachnophobia. There is really no substitute for getting out from behind the computer screen, television, or even the book or magazine and going exploring outside your home. Your very backyard can hold amazing surprises to rival the most exotic creatures of the Amazon.

Sources: Hillyard, Paul. 1997. Collins Gem Spiders Photoguide. Glasgow: Harper Collins Publishers. 254 pp.
Kaston, B. J. 1978. How to Know the Spiders (Third Edition). Dubuque, Iowa: Wm. C. Brown Company. 272 pp.
Ramirez, Martin G., Estelle A. Wall, and Monica Medina. 2003. “Web orientation of the banded garden spider Argiope trifasciata (Araneae, Araneidae) in a California coastal population,” The Journal of Arachnology 31: 405-411.
Tolbert, Wayne W. 1979. “Thermal stress of the orb-weaving spider Argiope trifasciata,” Oikos 32(3): 386-392.