Wednesday, November 30, 2011

Wasp Wednesday: Gall Wasps

Evidence of the activities of wasps can be found even when the insects themselves are long gone. Their mud or paper nests remain affixed to branches, and beneath the eaves of our homes. Sometimes, however, those nests are not recognizable as such. Plant galls are one example of this.

Many types of organisms can create galls. Flies, aphids, adelgids, mites, nematode worms, bacteria, viruses, and even fungi can stimulate abnormal plant growth, but the gall wasps of the family Cynipidae are perhaps the most common culprits. There are nearly 2,500 species worldwide, more than 750 of those occurring north of Mexico. Here in North America, the overwhelming majority of gall wasps are associated with just two groups of plants: the oak family and the rose family.

Nothing about the biology of cynipids seems to be very straightforward. Most species present an “alternation of generations” life cycle as figured in the diagram below from Some Plant Galls of Illinois. The spring population is normal, with winged adults of both genders emerging and mating to create the next generation. There is also an “agamic” generation represented only by females. These insects, which typically emerge in late autumn or winter, are wingless, and capable of reproducing without insemination by males. This kind of asexual reproduction is termed “parthenogenesis,” and many insects are capable of it. I found this example of just such an agamic female gall wasp on Thanksgiving day at the Cheyenne Mountain Zoo in Colorado Springs.

The large, hard galls most obvious to us are the ones produced *by* the spring bisexual generation, and the ones from which the asexual winter generation emerges. The spring galls are soft, small, and inconspicuous, usually on buds, flowers, or young leaves of the host plant.

Chemical compounds introduced by the adult female wasp in the course of laying her eggs, and/or by the larval wasp in the course of feeding, are probably responsible for the form and size of the gall produced, stimulating the expansion of cells in the host plant’s tissues as well as the type of growth in the vicinity of the insect. One can often determine at least the genus of the wasp by examining the gall it forms and knowing the exact host plant. The gall, below, for example, is a “Mossy Rose Gall,” produced by Diplolepis rosae, a species probably introduced from Europe in the course of cultivating roses. This specimen was also imaged at the Cheyenne Mountain Zoo.

The rough oak bullet galls pictured below are solid. Here on the Front Range, three species of wasps in the genus Disholcaspis create these kinds of galls on one host plant: Gambel’s Oak (aka “Shin Oak”), Quercus gambelii. I have observed that oaks are either gall-free or nearly so, or very heavily infested.

Ironically, galls rarely cause more than mere cosmetic “damage” to the host plant. An affected tree or shrub won’t win a beauty contest, but neither is it likely to keel over.

Much remains to be learned about galls and their makers, perhaps because so many other insects exploit galls and/or parasitize gall wasp larvae. Collect a large number of galls and you are as likely to raise an assortment of parasitic wasps as you are the gall wasps you would expect. Further complicating matters, still other insects lay their eggs in galls because of the abundance of food that galls present, and their nutritional value. These “houseguests” are called “inquilines” that live off the work of the gall wasp mother, but that do not affect the survival of her offspring.

Should you decide to take up the study of gall wasps, you will be in good company. Dr. Alfred C. Kinsey (yes, that Alfred Kinsey of human sexuality fame) began his career by spending two decades studying cynipids at Indiana University. I’ll be grateful if I can identify two other types of galls that appear on Gambel’s Oak. One is a leaf gall (top image in this post), and the other is a more linear twig gall.

Sources: Winterringer, Glen S. 1961. Some Plant Galls of Illinois. Springfield: Illinois State Museum, Story of Illinois No. 12. 51 pp.

Sunday, November 27, 2011

Spider Sunday: Spider Sex Ed

Just to clarify, this lesson is for people, not spiders. Spiders already know how to do it. Wait, that didn’t come out right, either. What I mean is, this is a primer on how to tell spider genders apart, and show why it is so difficult to properly identify your average arachnid.

Immature spiders cannot be identified to species (sometimes not even to genus) because they lack developed external genitalia that are species-specific. It is even more complicated than that because more “primitive” types of spiders don’t have complex genitalia anyway. Tarantulas, trapdoor spiders and their allies, collectively known as the Mygalomorphae, don’t have fancy equipment.

Next up on the ladder from mygalomorphs is another large clade called Haplogynae. The term has Greek roots and roughly translates to “half woman.” Among familiar haplogyne spiders are crevice weavers (Filistatidae), recluse spiders and their kin (Sicariidae), cellar spiders (Pholcidae), and spitting spiders (Scytodidae). Mature female haplogynes have a relatively simple genital opening known as the gonopore, accessed by the male through her “epigastric furrow.” The epigastric furrow is a simple transverse slit on the underside of the female’s abdomen.

Male spiders of all species do not have a penis, so they have evolved to use their pedipalps as intromittent sex organs to transfer sperm to the female. Pedipalps are the leg-like mouthparts nearest the spider’s face. The male spider prepares himself by spinning a small sheet of silk called a “sperm web.” He then extrudes seamen onto the sheet and sucks it up into a reservoir inside each pedipalp. He is now ready to go hunting for a mate. Males always wander to find a mate, even those species normally confined to webs.

Male mygalomorph and haplogyne spiders have no need for elaborate pedipalps because the female’s genital opening is correspondingly simple. Not so with the most highly-evolved spiders, the Entelegynae. Greek for “whole woman,” the term describes the much more complex genitalia of both genders. The overwhelming majority of non-fossil spiders fall within this group.

Sperm from the male goes into the female’s oviduct during mating in haplogyne spiders; and the sperm exits the same duct when the female lays her eggs. The sperm goes in one duct (copulatory duct) and out another (fertilization duct) in entelegyne spiders. Females of all types of spiders are capable of storing sperm from one mating for use their entire reproductive lives. This storage tank is called the spermathecae.

Female entelegyne spiders usually have a sclerotized (hardened tissue) “door” to their genitalia, located on the underside of the abdomen just above the epigastric furrow. This apparatus is called an epigynum (image above). It is usually composed of two openings, such that the structure has a symmetrical appearance. It is key to identifying many spiders to genus and species that otherwise look virtually identical to other, unrelated spiders.

The epigynum is more like a “lock” to the spider itself, as only males of the same species are able to mate with her. The male’s pedipalps are correspondingly complex, the “keys” to her “lock.” Male spiders that are one molt away from adulthood are termed penultimate and their pedipalps are swollen but not completely formed. The terminal segment changes radically with that last molt.

The image above shows the ventral (underside) view of the pedipalp of a mature spider. The dark, circular line is the “embolus,” the appendage that enters the female’s epigynum. The area behind the embolus is the “bulb” in which the sperm is stored. The bulb rests inside the cup-like dorsal plate called the “cymbium.” The pedipalp can also have various processes and projections on the cymbium and/or the patella or tibia segments.

Anyone who is serious about identifying spiders will not be able to avoid journal articles and books filled with images not of whole spiders, but their genitalia. Figuring out which end is up and exactly which parts the text is describing is a lot like solving a puzzle. It can be quite rewarding. Heck, just look at all the fun I’m having.

Sources: Ubick, D., P. Paquin, P. E. Cushing, and V. Roth (eds). 2003. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

Wednesday, November 23, 2011

Wasp Wednesday: Ant-queen Kidnappers

It is thanks to the book Big Game Hunting in the City Parks that I learned as a child of the “Ant-queen Kidnapper” wasps in the genus Aphilanthops. The captivating account by author Howard G. Smith of one of the female wasps hunting and transporting her prey was just too amazing to believe. Turns out it is a true story, just seldom witnessed.

The genus Aphilanthops, in the family Crabronidae and subfamily Philanthinae, occurs only in North America, including Mexico. There are four species, and at least two of them prey on on the winged queens of ants in the genus Formica. They can easily be mistaken for beewolf wasps in the genus Philanthus, but the inner eye margins of Aphilanthops are straight, not emarginated (notched) as they are in beewolves.

You are most likely to encounter the adult wasps as they drink nectar from flowers. The specimen of A. frigidus shown here was spotted in South Deerfield, Massachusetts in the late morning of July 19, 2009. This species ranges across much of the continent from Nova Scotia to British Columbia, and south along the major mountain ranges to the Carolinas, New Mexico and Arizona, and central California (mostly along the coast).

How the relationship between these wasps and their prey evolved is beyond me, but timing is truly everything in this case. The adult female wasp must be ready to take advantage of the short window in which ant colonies swarm. Ant colonies liberate males and new queens typically only once each year. Several ant nests must do this simultaneously to facilitate exchanges in genetic material and thus prevent inbreeding. So, the ant-queen kidnappers don’t have much time to apprehend their victims. Maybe only one day.

Each female Aphilanthops frigidus excavates her own nest burrow, usually in flat or gently sloping sandy soil. Several wasps usually nest in close proximity to one another, but whether they are actively competing for prey from the same ant nests is not obvious. The burrow descends underground at about a forty-five degree angle and terminates in a “waiting room” at 12-25 centimeters below the surface. Up to four ant queen victims are stored in the cell while the wasp constructs additional cells that will host her offspring. These “brood cells” may be 23-45 centimeters underground. Two to three ants are stored in each brood cell, a single egg laid on one of the victims. The cell is then plugged, and the wasp then addresses the next cell. Just how many brood cells are typical of a single nest is unknown. Once finished provisioning all the cells, the was fills in the burrow entrance with additional soil.

Accounts of attacks on the ant queens vary. Howard Smith reports that ant queens are attacked almost immediately upon emerging from the nest. Other observations conclude that the ants are attacked upon landing after their nuptial flights. At some point, the wasps detach the wings of their victims before storing them. The ants are flown back to the nest threshold where they are laid while the wasp inspects the interior of the burrow, then re-emerges to drag the ant down the tunnel by an antenna.

There are no observations of any species other than A. frigidus, so there is a lot to be learned in the future. The most common species I found in Arizona was A. hispidus (image above and below), which is abundant on the blossoms of Seepwillow (Baccharis salicifolia) in August and September. A. frigidus is active mostly from late June to mid-August, at least in New York state where Howard E. Evans studied that species.

Ant-queen kidnappers are not immune from their own villains, principally the “satellite flies” in the family Sarcophagidae. Senotainia trilineata is a confirmed parasite that lays its larvae (yes, the female fly “larviposits”) on the ant victims during their transport to the wasp’s burrow. Metopia leucocephala and Euaraba tergata are also prime suspects in nest failures, as they have been observed loitering in the vicinity of nest aggregations.

Consider doing your own “stake-out” at any wasp nest. Make a video if you are able. Chances are you can add to our scientific knowledge, if not make pioneering discoveries about prey and parasite relationships, seasonality, and other natural history.

Sources:Bohart, R. M. and E. E. Grissell. 1975. “California wasps of the subfamily Philanthinae (Hymenoptera: Sphecidae),” Bulletin of the California Insect Survey 19: 1-92.
Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Krombein, Karl V. and Paul D. Hurd, Jr. 1979. Catalog of Hymenoptera in America North of Mexico Vol. 2 Apocrita (Aculeata). Washington, DC: Smithsonian Institution Press. Pp. 1199-2209.
Smith, Howard G. 1969. Hunting Big Game in the City Parks. New York: Abingdon Press. 240 pp.

Sunday, November 20, 2011

Spider Sunday: Coras

Some spiders are so strange that they defy even experts to properly classify them. Such is the case with the genus Coras, which includes some very common species like C. medicinalis that spin funnel-like webs in and around human structures as well as natural settings.

First described by Nicholas Marcellus Hentz in 1821, C. medicinalis was placed in the genus Tegenaria. Charles Athanase Walckenaer put it in the genus Clubiona in 1837, but this move was not accepted by the bulk of his peers. So, he returned the species to the genus Tegenaria but changed the species to T. nemorensis. Hentz reasserted his intial name on two occasions, in 1847 and 1867. Eugen von Keyserling, in 1887, proposed Coelotes as the proper genus, and urbanus as the species name. Have I lost you yet? No? Good, because it gets more complicated still.

Eugene Simon published a revision of Coelotes in 1898, creating the genus Coras and resurrecting Hentz’s species name: Coras medicinalis thus achieving its currently accepted name. James Henry Emerton still broke ranks with his colleagues in 1902, assigning this species the name Tegenaria (subgenus Coelotes) medicinalis. John Henry Comstock apparently had the final word in 1912, asserting Simon’s revision as the official status for the species.

Even more astonishing, the genus Coras has bounced between families like a taxonomic pinball. Frederick Octavius Pickard-Cambridge originally placed Coras in the subfamily Coelotinae of the family Agelenidae. This genus, as well as the closely-allied genus Wadotes stayed in the Agelenidae until 1986, when Joerg Wunderlich moved them to the family Amaurobiidae. What was wrong with that, you ask? Well, one of the defining characteristics of the Amaurobiidae is the presence of an “extra” plate-like silk-spinning organ called a cribellum, located just in front of the spinnerets. The thing is, Coras and Wadotes don’t have this structure. Just this year the two genera boomeranged back to the Agelenidae, though I cannot presently find the journal article confirming this.

Thankfully, the biology of Coras is more straightforward. There are fifteen species in North America, all of them found principally east of the Mississippi River (southeast Canada south to Florida and west to Wisconsin and Louisiana). The genus can be identified in part by the eyes. The anterior median eyes are larger than the anterior lateral eyes. That means that the row of eyes nearest the jaws has the middle pair larger than the outer pair. I find the pattern of dark lines on the carapace to be fairly diagnostic as well.

Their webs are generally not as large as those of other funnel-web spiders, perhaps because the spiders themselves are not that large. Mature females average between 8 and 13 millimeters in body length, males 8-10 millimeters. Adult spiders are found in summer and fall. Egg sacs are probably produced in autumn since both adult and juvenile specimens have been observed hibernating in silken retreats under rocks during the winter months.

The webs may be well off the ground as evidenced by the one shown above. It was attached to the exterior of a pump house in Mount Sugarloaf State Reserve in South Deerfield, Massachusetts. The multiple retreats, instead of singular, is typical of the genus, too. These are spiders of forested habitats that also build their webs from beneath stones, from crevices in rock walls, and from loose bark on trees and logs. They are not strangers to basements or cellars, though, so look for them there as well.

Coras medicinalis acquired its species name from Hentz’s knowledge that the webs of this spider were used to make a tincture (alcoholic extract) for the relief of fevers back in the 1800s. Good to know we have advanced in our pharmaceuticals since then, leaving us free to simply enjoy these spiders on their own merits.

Sources: Bradley, Richard A. 2004. In Ohio’s Backyard: Spiders. Columbus, Ohio: Ohio Biological Survey Backyard Series No. 4. 185 pp.
Cates, Jerry. 2011. ”Araneae: Agelenidae: Funnel-web Spiders,” Bugs in the News. November 5, 2011.
Gaddy, L. L. 2009. Spiders of the Carolinas. Duluth, Minnesota: Kollath+Stensaas Publishing. 208 pp.
Howell, W. Mike, and Ronald L. Jenkins. 2004. Spiders of the Eastern United States. Boston: Pearson Education, Inc. 362 pp.
Levi, Herbert W. and Lorna R. 1968. Spiders and their Kin. New York: Golden Press. 160 pp.
Moulder, Bennett. 1992. A Guide to the Common Spiders of Illinois. Springfield, Illinois: Illinois State Museum Popular Science Series, Vol. X. 125 pp.
World Spider Catalog.

Wednesday, November 16, 2011

Wasp Wednesday: Anacrabro ocellatus

You can often get a clue as to the identity of a wasp by noting what kind of prey she is toting. Ok, so this only works with female wasps, and it is largely a matter of luck to catch one in the act of subduing or transporting prey. Still, if you see a little (6-7 mm) black and yellow wasp in possession of a plant bug in the family Miridae, it is probably Anacrabro ocellatus, in North America anyway.

The funny thing about the image above is that until I uploaded it to my computer and cropped it, I thought the subject was a yellow-faced *bee* in the genus Hylaeus. I shot this by the Campus Pond on the University of Massachusetts campus in Amherst on August 6, 2009.

Anacrabro is a genus with two species north of Mexico. A. ocellatus, with two subspecies, is widespread east of the Rocky Mountains. A. boerhaviae is recorded in the extreme southwestern U.S. and in Mexico.

Most of the other genera in the tribe Crabronini, family Crabronidae, are fly-killers that use species of the order Diptera as food for their offspring. By contrast, Anacrabro seeks plant bugs in the family Miridae, order Hemiptera. Specifically, A. ocellatus hunts almost exclusively for adults of the “Tarnished Plant Bug,” Lygus lineolaris, pictured below.

Tarnished Plant Bugs are certifiable pests. They are generalist feeders that afflict over half of all cultivated plant species in the continental U.S. Substantial numbers of them can certainly cause severe damage to crops and garden plants. Thank goodness the wasp likes to stock them in the larder for her brood.

Anacrabro ocellatus is a “fossorial” wasp, meaning that the female digs a burrow in the soil for her nest. Each wasp digs a nearly vertical tunnel 9-16 centimeters deep, though the shaft may wind or loop in hard-packed soil. Short side tunnels may be present half-way down, but more typically longer side burrows diverge in various directions near the bottom of the main tunnel. Very short passages radiate from these longer side tunnels, each terminating in a single cell. It is into these chambers that 4-9 prey bugs are placed as food for a single wasp larva per cell. Each nest has from one to ten or so cells. Do the math and that makes Anacrabro a pretty heroic pest control species. Females may construct more than one nest, too.

Studies have shown that this wasp suffers relatively little from nest parasites, though in some instances the contents of the subterranean cells were preyed upon by ants. The nest entrance is often concealed by overhanging weedy vegetation, and the female wasp takes pains to disperse the excavated soil, so perhaps such strategies pay off in reduced incidences of parasitism.

Between hunting and nest-digging, females refresh themselves on flower nectar, especially at the umbels of wild carrot (aka “Queen Anne’s Lace,” Daucus carrota). They also visit goldenrod (Solidago), milkweed (Asclepias), and other flowers. That is where you are most likely to encounter them.

Besides its prey preferences, Anacrabro can be separated from very similar-looking wasps such as Ectemnius, Lestica, and Crabro by the very concave underside of the abdomen.

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp. (and source of the drawing above, by Judy Jay).
Kurczewski, Frank E. and David J. Peckham. 1970. “Nesting behavior of Anacrabro ocellatus ocellatus (Hymenoptera: Sphecidae),” Ann Entomol Soc Am 63(5): 1419-1424.

Sunday, November 13, 2011

Spider Sunday: Spiders 'R' Us


Yesterday, the people who brought you SpiderIdentification.org launched literally a “brand” new website, Spiders.us. The new website will have an expanded range of more traditional content, not the interactive forum of its predecessor. Not to worry, you can still post “mystery spiders” to the Facebook page for SpiderIdentification.

Spiders.us is dedicated to being your headquarters for everything “spider” in the United States and Canada. The aim is to be accurate above all else, for there exists so much misinformation, contradictory information, and downright myth, superstition and urban legend that it is no wonder so many people are fearful of spiders. We empathize and promise to put the squeamish and scared at ease as best we can.

We will also defend spiders for the important roles they play in nature, pest control, medicine, engineering and other economic and cultural realms. Here you will find:

  • Help in identifying the “mystery spider,” or even its web, in your home, office, yard, or garden.
  • Help in avoiding and preventing spider bites.
  • The latest news on spiders from the scientific community.
  • Educational resources from online articles to scientific papers.
  • Articles on the positive impacts of spiders on human culture.

We also look forward to hearing from you about how we can make this website more user-friendly and comprehensive. While we see our audience as people with little or no prior knowledge of the arachnid world, you will also find material that is more sophisticated, suitable for naturalists, librarians, teachers, and even scholars.

I am personally looking forward to this new venture, creating content for the site and learning new things myself along the way. Won’t you join me?

.

Wednesday, November 9, 2011

Wasp Wednesday: Passaloecus

I am still learning the very basics of taking images of insects, like using a flash even when it doesn’t look like I need to. Therefore, I have only one respectable image of a live specimen of one of my favorite wasps, in the genus Passaloecus. They are predators of aphids, but are themselves pretty small, averaging 6-8 millimeters in body length.

Besides carting aphids back to their nests as food for their larval offspring, the female wasps feed on “honeydew,” the sweet liquid waste product secreted by aphids in copious amounts. Wasps of all kinds eagerly lap up the sticky fluid from the surface of leaves. That is how I was able to get the image above, on the leaf of a young aspen tree at the Cheyenne Mountain Zoo in Colorado Springs on July 13, 2011.

The genus Passaloecus, pronounced Pass-uh-LEE-kus, is in the wasp family Crabronidae, subfamily Pemphredoninae. There are approximately sixteen species of Passaloecus in North America, collectively found across the entire continent. While they are small and relatively non-descript black insects, I find I can recognize them fairly easily by their white or ivory jaws.

These are solitary wasps that you can actively attract to your yard by providing artificial nests for them. They nest in pre-existing beetle borings, and/or hollow stems and twigs, and vacant galls which they partition into a linear series of cells. As their habitat gets converted to subdivisions and dead, standing trees are preemptively felled to avoid lawsuits, these wasps face a real estate shortage. Simply drilling holes about 3/16th of an inch in diameter and to a depth of four inches or so into a wooden block, and placing the block in a sheltered situation well off the ground, you can provide housing for these beneficial bugs.

The nest tunnel is divided into cells with partitions usually made of plant or tree resin. Each cell is provisioned with a number of paralyzed or dead aphids (from six to over sixty according to the literature) and an egg laid on one of those victims. The female wasp may sting an aphid victim, or crush it to death in her jaws, before taking it back to the nest.

Nests of Passaloecus ithacae may contain six to twelve cells each (Krombein, 1967). There are two generations annually, at least in Erie County, New York. Nests of this and other species of Passaloecus are subject to parasitism from the cuckoo wasp Omalus aeneus and the ichneumon wasps Poemenia albipes and P. americana.

We tend to think of lady beetles and lacewings as the prime predators impacting aphid populations, but Passaloecus and related genera of wasps clearly have an effect as well. Perhaps we need to re-think our assumptions and expand our natural allies in pest control to include wasps (Corbet & Backhouse, 1975).

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley: University of California Press. 695 pp.
Corbet, Sarah A. and M. Backhouse. 1975. “Aphid-hunting wasps: a field study of Passaloecus,” Trans R Entomol Soc Lond 127(1): 11-30.
Fricke, J. M. 1993. “Aphid prey of Passaloecus cuspidatus (Hymenoptera: Sphecidae),” Gt Lakes Entomol 26(1): 31-34.
Krombein, Karl V. 1967. Trap-Nesting Wasps and Bees: Life Histories, Nests and Associates. Washington, DC: Smithsonian Press. 496 pp.
http://researcharchive.calacademy.org/research/entomology/Entomology_Resources/Hymenoptera/sphecidae/Genera_and_species_pdf/Passaloecus.pdf

Monday, November 7, 2011

Spider Sunday: Mystery Solved

Note: This post originally appeared on Sunday, November 6, but I pulled it in the wake of what turned out to be mostly a misunderstanding. After careful deliberation I am resurrecting the story. I think it is instructional in terms of how problems like this are resolved. I normally do not charge a fee for a simple identification, but this was an exceptional case involving a corporation with much to lose without intervention.

This past Wednesday, November 2, I was presented with a unique opportunity to solve an arthropod mystery for a corporate client. A friend in state government sent me a message on Facebook that morning asking myself and another colleague who we would recommend for identifying spider specimens for a company in an Atlantic coast state. I wrote back that the inquiring party could send specimens to me, but that I would charge a modest fee for my expertise. My government friend thought that seemed reasonable and put me in touch with the company representative.

Later that morning I received a phone call from the Director of Regulatory Compliance for the company suffering from a “spider infestation” in a recent shipment of merchandise from overseas. He decided he would overnight specimens to me for examination.

The next morning, the company rep e-mailed me with two images of the spiders in question. I was pleasantly surprised by the detail in those pictures:

It was clear to me from the images that the spiders were some kind of “cellar spider” in the family Pholcidae, but I could not conclude what genus, let alone species, without putting actual specimens under a microscope. At least I could tell him that the arachnids were nothing considered to be dangerously venomous according to current scientific understanding. Time was of the essence and I hoped that my reply to his e-mail might be sufficient.

I received a message from FedEx with a tracking number for the package, and discovered that I would not receive the shipment until Friday morning. Meanwhile, I did not hear back from my company contact.

Indeed, I heard a knock on my door around 10:00 AM on October 4, and there was the FedEx delivery person with a box for me. Interestingly, he seemed quite eager to part with the parcel….

I was amused to find that inside this rather large box was a great quantity of bubble-wrap and a teeny-tiny little vial with a single spider inside. I believe the spider was actually alive when it was packed up, though it was deceased when it arrived. It was still limber and in no way compromised in its anatomical integrity.

I gently placed the creature into a glass petri dish and under my microscope. It was immediately apparent that I had an immature specimen, which would make identification more difficult than it would be with an adult specimen. Still, I broke out my “bible,” the Spiders of North America: an identification manual, turning to the family Pholcidae. The key to genera was sufficient enough for me to conclude that the spider belonged to the genus Pholcus: eight eyes, not six; no pit or groove in the carapace.

Up until recently, it would have been safe to extrapolate to the species P. phalangioides, the “Long-bodied Cellar Spider,” a very abundant and widespread species. However, I learned from my arachnologist colleague that another species of Pholcus, P. manueli, is expanding its range in the United States. Further, there are evidently a number of undescribed species in the genus.

I called the company representative today with the verified identification.

Wednesday, November 2, 2011

Wasp Wednesday: Pollen Wasp

Today, as I write this, there is snow on the ground and the temperature is somewhere in the 20s (Fahrenheit). You can’t blame me for harkening back to July 11 when it was warm and I was hiking with friends in Emerald Valley near Cheyenne Mountain here in the Front Range of Colorado. One of the insects that excited me the most that day was Pseudomasaris vespoides, one of the “pollen wasps” that stands in such stark contrast to its social and predatory relatives.

Pollen wasps comprise the subfamily Masarinae in the family Vespidae. They collectively occur across the globe, in western North America, southwestern South America, northern and southern Africa, southern Europe, central Asia, and most of Australia, absent from tropical regions. Only the genus Pseudomasaris exists in North America, with 14 species.

These are solitary wasps, each female constructing her own mud nest and provisioning each cell with pollen and nectar, more like a bee than a wasp. The wasps visit Penstemon, or Phacelia and Eriodyction almost exclusively, with additional records for some other flora genera. This pollination relationship is termed “oligolectic” when an insect is obliged to harvest pollen from such a limited diversity of flowers.

The female Pseudomasaris vespoides that I observed on that July day were all visiting Penstemon blossoms. I did not see any males, but populations of this wasp peak in late June with males emerging before females, so their absence later in the year would not be peculiar. Males, easily identified by their very long, clubbed antennae, patrol patches of flowers likely to be visited by females. This is in contrast to the hilltopping behavior of P. maculifrons that I addressed in a previous post.

Females fashion earthen nests comprised of several cells. While most Pseudomasaris adhere their nests beneath stones or other sheltered situations, P. vespoides tends to attach its nests to twigs out in the open, like the one shown below, from Catalina State Park in southern Arizona. The nests may be parasitized by the cuckoo wasp Chrysurissa densa.

P. vespoides is a relatively widespread species, occurring from Washington state south to California, Arizona, and New Mexico, east to Wyoming, Nebraska, and South Dakota. Females and males are about the size of your average yellowjacket wasp and can easily be mistaken for their social cousins. Pollen wasps, however, do not have the longitudinal fold that other vespid wasps display when the insects are at rest. Pollen wasps also have clubbed antennae, whereas other vespids do not.

Sources: Gess, Sarah K. 1996. The Pollen Wasps: Ecology and Natural History of the Masarinae. Cambridge, Massachusetts: Harvard University Press. 340 pp.
Richards, O. W. 1963. “The Species of Pseudomasaris Ashmead (Hymenoptera, Masaridae). University of California Publications in Entomology 27(4): 283-310.