Sunday, October 30, 2011

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.

Friday, October 28, 2011

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 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 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.

  • Wednesday, October 26, 2011

    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).

    Sunday, October 23, 2011

    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.

    Wednesday, October 19, 2011

    Wasp Wednesday: Western Yellowjacket

    Notorious. That describes the Western Yellowjacket, Vespula pensylvanica (and yes, the species name is spelled correctly). I recall this social wasp from my childhood in Portland, Oregon where it was a constant presence at picnics, barbecues, and garbage cans at the zoo and every other urban park. Here in Colorado Springs they are equally pestiferous, and persist deep into the fall.

    Each year, the Western Yellowjacket colony cycle begins with queens searching for nesting sites. These females are larger, and more yellow in color than the worker caste. They typically emerge from their winter hibernacula sometime between March and April, though it may take awhile for a queen to find a suitable subterranean niche where she can start building her nest. I imaged the queen below at the Cheyenne Mountain Zoo on July 9, 2011, so she still had no help from workers in constructing her nest.

    Once the queen’s worker offspring can contribute, the colony and nest quickly expand in size. Mature nests, based on records from Pullman, Washington and La Grande, Oregon, can exceed a population of 2,000 workers (average about 1,800) and contain 4,000 cells or more in the paper combs.

    Nests are usually located in abandoned rodent burrows ten to fifteen centimeters below the surface of the soil, with entrance tunnels ten to thirty centimeters long. There is often a mud turret surrounding the entrance hole. Look for yellowjackets coming and going from the same spot to locate a nest entrance. You can approach closely to watch their activity without arousing the occupants, but run a lawnmower over the nest and watch out! One of my elementary school science teachers told me he once drove a stake right through a nest. That could not have been a pleasant experience.

    Western Yellowjackets are best known for their aggressive scavenging behavior. They have to secure large quantities of protein to feed the larvae in the nest, and the workers take that job seriously. It is much easier to haul away a chunk of your tuna sandwich, chicken leg, or burger than it is to go kill a series of small insects. Still, this species does its fair share of scavenging road kill and preying on true bugs, spiders, flies, grasshoppers, even slugs.

    The adult wasps need carbohydrates to fuel their active lifestyle, so that is why they crawl into your soda can. Normally, in nature, they prefer the sweet waste products secreted by aphids and scale insects. This “honeydew” is like the Nectar of the Gods to social wasps. Last week I imaged several workers lapping up the honeydew of Cinara conifer aphids on a pine tree at the Cheyenne Mountain Zoo.

    The last chapter in the annual colony life cycle is the production of new queens and males. These reproductives are liberated at the end of the season and they fly out to find mates from other colonies. The males, with their long abdomens and antennae, seem to congregate around the tops of small trees where they perch to await passing females. The males may dislodge each other from prime lookout posts, but they don’t have stingers and such squabbles are therefore not life-threatening.

    Western Yellowjackets can be “bad” some years, with much higher than normal population densities. This usually occurs when a warm, dry spring season allows queens to get a head start on establishing colonies. The result can be worker wasps wreaking havoc on fruit tree orchards, logging camps, and outdoor recreation destinations later in the summer.

    The Western Yellowjacket is exactly that: a western North American species ranging from southern British Columbia, Alberta and Saskatchewan south through the Pacific coast and Rocky Mountain States, all the way to Arizona and New Mexico at higher elevations. There are scattered records across the northern Midwest as far east as Michigan; and this species has been introduced to Hawaii as well.

    Source:Akre, Roger D., Albert Greene, et al. 1981. The Yellowjackets of America North of Mexico. Washington, DC: USDA Agriculture Handbook Number 552. 102 pp.

    Sunday, October 16, 2011

    Spider Sunday: Triangle Spiders

    The following is a “reprint” of a blog entry for September 10, 2009.

    An outing to the Westfield River in Hampshire County, Massachusetts last Sunday, September 6, included a stop at the Knightville Dam, where a unique arachnid awaited my discovery. There, among the goldenrods, asters, and ornamental black locust trees I found two triangle spiders, named for the shape of their web: a triangle that is essentially the sector of an orb web. The reduced size of the snare is just one puzzling feature of these amazing spiders.

    Triangle spiders belong to the genus Hyptiotes (pronounced Hip-tee-OH-teez) in the obscure family Uloboridae. They are part of a larger group of arachnids called “cribellate spiders.” Cribellate spiders all share one feature in common: an extra spinning organ called a cribellum, located adjacent to the normal group of spinnerets. The cribellum issues a special type of silk that the spider literally “fluffs up” using a comb-like organ called a calamistrum, located on each hind leg.

    Perhaps even more amazing than the “accessories” that uloborids have is what they lack. These are the only spiders in North America that do not have venom glands. That’s right, they are non-venomous spiders. So, you ask, how then do they subdue their prey? That is a great question for which I have not the foggiest answer. They probably do an extra-good job of wrapping their prey in silk, but not just any silk.

    The cribellate silk threads in the part of the web designed to trap insects is not sticky like you would expect. Instead, it is tangled, and this is apparently just as effective as little droplets of glue.

    Once it has erected its snare, the triangle spider sits on the thread near the tip of the twig or grass stem to which the apex of the triangle is secured. Depending on which book or article you believe, the spider either bridges a gap in this anchor thread, or simply perches there and reels in the slack line to render it taut. When a prey insect impacts the web, the spider then instantly releases the anchor thread, causing the web to rebound, further entangling the prey.

    This feat of engineering and strength is performed by a very small animal. Even an adult female Hyptiotes is only 3-4 millimeters long. Males are 2-3 millimeters at maturity. Simply spotting one of these spiders is cause for self-congratulations for any naturalist.

    There are four species of Hyptiotes in North America, three of which are chiefly western in their geographic distribution. The one shown in the image here is Hyptiotes cavatus, the sole eastern species.

    Keep a sharp eye out for triangle spiders. The webs are mostly built about waist-high in weeds, on bridges and other structures, and twigs of trees and shrubs.

    Wednesday, October 12, 2011

    Wasp Wednesday: Prairie Yellowjacket

    Arriving in Colorado Springs in early October, I was not optimistic that I would find many, if any, wasps still active in the chilling air. Much to my surprise there are still some on the wing, even at high altitudes. Monday, October 10, Heidi and I traveled up into the Front Range to Cripple Creek and the surrounding area. There, walking around on the snow, I found a male Prairie Yellowjacket, Vespula atropilosa.

    Heidi remarked that she thought the Western Yellowjacket, Vespula pensylvanica was the only species of that genus living in the area. Actually, there are six species total known from Colorado. Yellowjackets could be considered mostly boreal in their distribution patterns, ranging south at higher elevations where the climate resembles that of higher latitudes.

    This particular specimen could have been blown up to its 9,000 foot or so location, too. The colonies of V. atropilosa tend to be smaller than those of more “urban” species, and usually decline earlier in the season, too, so I was somewhat surprised to see this one.

    This male exemplifies the yellow or “xanthic” phase of this species. They also come in a black or “melanic” phase that is more black than yellow, as shown in the diagram below from Roger D. Akre’s The Yellowjackets of America North of Mexico (USDA Agriculture Handbook No. 552, 1981), and another specimen I imaged on October 13 in Colorado Springs.

    The Prairie Yellowjacket nests preferentially in abandoned rodent burrows. Nests have also been discovered in tree hollows, under steps, and between the walls of houses. One truly aerial nest was found in Pullman, Washington, but this is decidedly an anomaly. The paper combs are surrounded by layers of “envelope,” typically rather coarse as is the case in most subterranean yellowjacket species. V. atropilosa nests are dirtier than most, with the bodies of deceased wasps and other debris incorporated into the paper envelope.

    The greatest number of workers in any of the nests studied by Dr. Akre and his colleagues was 504. These are not your picnic-harassing, garbage-gathering yellowjackets, either. They have retained their predatory nature and hunt mostly spiders, harvestmen, flies, insect larvae, and true bugs as food for the larvae back in the nest. Adults feed on aphid honeydew and flower nectar to fuel their flight.

    The Prairie Yellowjacket is restricted to western North America, ranging from central British Columbia south and east through southern Alberta, Washington, Oregon, California, Idaho, western Montana, Wyoming, Utah, most of Colorado, and northern New Mexico and Arizona. It avoids nesting in truly urban locations in my experience, though nests in yards are apparently not uncommon.

    I look forward to finding more interesting yellowjacket species here in the Rocky Mountains, and I reserve the right to revisit this particular species in future blog posts.

    Sunday, October 9, 2011

    Spider Sunday: Arachtober, 2011

    It seems like only yesterday that I announced the annual Flickr photo group ”Arachtober” at my other blog, Sense of Misplaced. Well, it is that time of year again, and this year’s edition of the online event is poised to be the best ever.

    One needs to have a Flickr account to join the Arachtober group. Then, you must be approved by the group administrator, though this is usually only a formality. Right now, group members can only post one image of a spider, scorpion, or other arachnid per day. Later in the month the limit will increase. The images you contribute should not be ones posted to your Flickr page in previous months.

    The fact that Arachtober falls in the same month as Halloween is no coincidence, but the goal of Arachtober is to celebrate the diversity, beauty, and positive impact of our arachnid friends. It is a perfect antidote to haunted house cobwebs and scary fake spider decorations.

    Once again I encourage all my arthropod-loving photographer friends to share their favorite images with an audience of other arachnophiles. Please see the above link to my original post for more information on the origin of the event. Thank you.