Makin' Paper

This has been an exceptional year for paper-making social wasps in the family Vespidae here along the Colorado Front Range. Most species of paper wasps and yellowjackets have been unusually abundant, much to the consternation of the average person who despises any stinging insect. However, there is much to admire about these industrious organisms, not the least of which is the amazing architecture of their nests.

Western Paper Wasp nest (Mischocyttarus flavitarsis)

Nests of most social vespids are made of repurposed or recycled cellulose from dead, woody plants and trees. The wasps manufacture the paper by scraping fibers and chewing them into a ball of pulp that is taken back to the nest and applied as a thin strip that soon dries into a surprisingly durable, stiff material.

Bald-faced Hornet worker scraping wood fibers

Paper wasps in the genera Polistes and Mischocyttarus here in Colorado make exposed paper combs that are frequently suspended under the eaves of buildings. Yellowjackets, including the Bald-faced "Hornet," Dolichovespula maculata, house their combs within a layered paper envelope. Species in the genus Dolichovespula build their nests above ground, usually in a tree, shrub, or among berry canes. Species in the genus Vespula normally build their nests underground in abandoned rodent burrows and other pre-existing cavities that they can expand by excavating around the nest.

Huge European Paper Wasp nest

I was surprised to find out that paper wasps will re-use old nests! One particularly impressive nest of European Paper Wasps (Polistes dominula) is situated under an overhang at my workplace in Colorado Springs. It appeared abandoned when I first started work there, but was quickly occupied and even expanded later in the season. This is an impressively large nest that would probably not fit on a dinner plate, very unusual for any species of Polistes.

Active nest of Bald-faced Hornets

I also discovered an active nest of the Bald-faced Hornet in North Cheyenne Cañon on August 21. Fortunately, it was far enough off the trail to not be a potential hazard to the many people that use the park; and far enough off the trail to make it difficult for anyone to destroy the nest. I went back a month later (September 18) and found the wasps had expanded the nest and changed its shape from oval to a roughly football shape. There was no evidence of activity, and indeed the colony cycle for this species is shorter than that of other social wasps.

Bald-faced Hornet nest on August 21

The same nest on September 18

Underground nests like that of the Western Yellowjacket (Vespula pensylvanica) and Prairie Yellowjacket (V. atropilosa) are more problematic because one can easily disturb an unseen nest with painful results. I only notice nests when my eye catches a steady stream of yellowjackets coming and going from a common point.

Western Yellowjacket nest entrance. Note exiting workers carrying soil pellets

Paper wasps are generally welcome predators of caterpillars and other soft-bodied insect pests. The Bald-faced Hornet is a predator of flies that is never a pest at picnics and barbecues. The same is true of the Prairie Yellowjacket. Meanwhile, the Western Yellowjacket is a scavenger that will take your lunch away from you given the opportunity. Gently waving your hand can eventually discourage the wasp's efforts.

Prairie Yellowjacket worker eating insect

We may have these wasps to thank for inspiring the invention of the paper that we use today. At least some accounts trace observations of wasps in ancient China to the origins of human papermaking.

Polistes metricus

Paper wasps tend to be quite variable in color and pattern, even within one species, so identifying them is not easy, even for experts. Case in point is differentiating the common Northern Paper Wasp, Polistes fuscatus, from the very similar Polistes metricus.

Dark specimens of the Northern Paper Wasp are nearly identical to Polistes metricus, a consistently dark species that I have found to be less abundant than P. fuscatus in areas where their geographic ranges overlap. One fairly reliable, if subtle, clue is the shape of the abdomen. Note that the abdomen of P. metricus is highly convex on the underside, creating a nearly acute angle with the underside of the petiole (stalk-like segment connecting abdomen with thorax). This is usually much less pronounced in P. fuscatus.

Another difference is in the face of the female wasps. Females of P. metricus have an almost completely red face, the black markings confined to the ocellar triangle. Ok, so what is an “ocellar triangle?” Most wasps have a trio of tiny, “simple” eyes at the top of the head, between the large compound eyes. These simple eyes are usually arranged in a triangular pattern. Females of the Northern Paper Wasp have the black marking extended from the ocelli to the base of the antennae. Males of both species have square, yellow faces.

Female P. fuscatus. Note black face; gently curved venter of abdomen
Female P. metricus. Note convex venter of abdomen.
Female P. metricus. Note all-red face.

Polistes metricus ranges from extreme southwestern Ontario and Maine south to Florida, and west to southern Ohio, Nebraska, Kansas, Oklahoma, and eastern Texas. The Northern Paper Wasp has a much larger geographic distribution.

I was fortunate enough to find three embryonic nests of P. metricus on a recent trip to Missouri. Two nests were under the exterior of a recessed door frame in Excelsior Springs. The other was under the roof of a sign and kiosk at Little Dixie Lake Conservation Area west of Kingdom City. These are typical nesting sites, though they can also be built among shrubbery and other more exposed locations.

Both the Northern Paper Wasp and P. metricus prey mostly on caterpillars, chewing up the larvae and feeding them to their own grubs back at the nest. Look for the adult wasps on flowers as they fuel themselves on nectar. They can also be seen around aphid colonies, lapping up the “honeydew” secreted by the aphids as a waste product.

Source: Buck, M., Marshall, S.A. and Cheung D.K.B. 2008. Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region. Canadian Journal of Arthropod Identification No. 5: 492 pp. (PDF version).

Wasp Wednesday: Polistes exclamans

Paper wasps in the genus Polistes are more diverse the farther south you go, reaching their zenith in tropical and subtropical climates. Global climate change may be nudging some species farther north, though, so it pays to keep your eyes open. One species that naturally ranges beyond the subtropics is the Common Paper Wasp, or “Guinea Wasp,” Polistes exclamans.

I recommend using the scientific name, as there is no official common English name. This is a widespread insect found from New Jersey south and west to Florida, Indiana, Illinois, Nebraska, Colorado, Arizona, and southern California. It also ranges into Mexico, and has been introduced to Hawaii; and there is one record for Ontario, Canada.

Look for their nests in sheltered places, such as beneath the eaves of homes. They will also nest in trees, but most of the time that I have found nests, they have been attached to some man-made structure. Here is one from beneath an interpretive sign on the hawk watch platform at Cape May Point State Park in New Jersey (October 17, 2010).

Here is another nest on the ceiling of a picnic shelter in the same park (October 3, 2012).

This is a fairly easy species to identify:

• Evenly patterned in red and yellow, usually with black coloration reduced to thin bands on abdomen (occasionally more extensive black markings, especially on top of thorax).
• Antennae banded with red, black, and yellow (most paper wasp species have antennae of one color).
• Size relatively small (forewing length 12-16.5 millimeters).

Like most paper wasps, this species preys on caterpillars that the worker wasps chew up and feed to the larvae in the nest. They feed on a wide variety of moth and butterfly caterpillars, including members of these families: Pieridae (white and sulphur butterflies), Hesperiidae (skippers), Noctuidae (owlet and tiger moths), Notodontidae (prominent moths), Sphingidae (sphinx moths or hawk moths), and Saturniidae (giant silkmoths).

You would think that social wasps in general would not be bothered by predators and parasites given the presence of many stinging adult wasps ready to defend the brood (eggs, larvae, and pupae), but such is not the case. Polistes exclamans can occasionally lose its entire brood to bird predation. The acrobat ant, Crematogaster laeviuscula can also destroy a nest. Partial losses can come from Elasmus polistis, a tiny wasp in the family Eulophidae that infests young paper wasp nests that are defenseless while the foundress is away foraging.

Note males on right have black on thorax and head

Irony of ironies, caterpillars of the pyralid moth Chalcoela iphitalis can take a toll due to their parasitic activities on the wasp larvae. The moths themselves are quite attractive:

This is one of the most studied of social wasps, and the literature cited below is only a fraction of the scholarly works devoted to P. exclamans. Despite this, the known distribution of the species has been clarified mostly through documentation by citizen scientists contributing their specimens and images to universities, museums, and websites like Bugguide.net that are monitored by professional entomologists. Keep up the good work, folks.

Sources: Buck, Matthias, Stephen A. Marshall, and D.K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5, 492 pp. (PDF version)
Starr, C.K. 1976. “Nest reutilization by Polistes metricus (Hymenoptera: Vespidae) and possible limitation of multiple foundress associations by parasitoids,” J. Kans. Entomol. Soc. 49(1): 142-144.
Strassmann, Joan E. 1981. “Parasitoids, Predators, and Group Size in the Paper Wasp Polistes Exclamans,” Ecology 62(5): 1225-1233.

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.

Wasp Wednesday: A Tropical Social Wasp

Attention: You. Yes, you. I welcome your images of mystery insects and spiders from anywhere in the world, and will blog the answer to share with others if I have your permission to publish the images. The following is one example of how this might appear.

I often receive inquiries through my private e-mail, asking if I could identify this insect or that spider, sometimes from other corners of the world besides the United States. This is always a welcome challenge, but the emphasis is usually on “challenge.” Not long ago, my friend Paul Kaufman sent me three wonderful images of a social wasp taken by Pablo Yoder, a missionary in Nicaragua. At least I recognized it as something in the family Vespidae, but there is a vast number of genera and species in the neotropics.

© Pablo Yoder

Thanks to Google image searches, I eventually pinpointed the wasp as the species Polybia emaciata. It is one of the few social vespid wasps that builds its nest of mud instead of paper. The more durable nature of the mud envelope allows the wasps to “hunker down” or flee when faced with a potential attack by a vertebrate predator. Contrast this behavior with the violent attacks launched by social wasps that build relatively flimsy nests of paper.

Enclosing a nest helps protect the eggs, larvae, and pupae that inhabit each cell in the horizontal layers of combs made by social wasps. Exposed combs are more vulnerable to predators and parasites since the adult wasps cannot be everywhere at once guarding each member of the brood.

© Pablo Yoder

So what is the wasp in two of these images doing with a big drop of water in its jaws? It is essentially bailing out the nest, keeping the mud from becoming saturated. It rains hard and often in the jungle. Even though the nests of wasps are usually ensconced beneath foliage in the rainforest canopy or understory, a good quantity of water still reaches those nests. The workers begin drinking the water, then walk to the edge of the nest and regurgitate droplets. The thick mud walls of the nests of this species take longer to become saturated than do paper nests of other species, but there is still cause for concern on the part of the nest inhabitants.

Nests of Polybia emaciata are typically inhabited by a small number of adult wasps. Colonies usually number between 100 and 500 wasps, while other species would have a much larger number. The nests vary in size from roughly nine centimeters to 22 centimeters in length, as least in one study in Panama (O’Donnell & Jeanne, 2002). The nests may also persist for several years due to their durability.

© Journal of Insect Science

O’Donnell and Jeanne elicited nest defense responses by tapping on the exterior of the nests, or blowing into the entrance hole. Most wasps would respond by rushing out of the nest and either attacking immediately or adopting an agonistic (warning) posture while perched on the exterior of the nest envelope. Not so with Polybia emaciata, which either flew away (though not abandoning the nest), or took refuge inside. Only sustained, escalated provocation resulted in the wasps exiting the nest, then pummeling and attempting to sting the researchers. Natural predators of tropical social wasps include birds, bats, and monkeys.

© Pablo Yoder

The diversity of wasps in the tropics, their survival strategies, and their relationships to other organisms is fascinating. I hope to one day see some of these remarkable insects for myself, but in the meantime I appreciate my readers sharing their own experiences and images.

Source: O’Donnell, Sean and Robert L. Jeanne. 2002. “The nest as fortress: defensive behavior of Polybia emaciata, a mud-nesting eusocial wasp,” J Insect Sci 2.3. 5 pp.

Wasp Wednesday: A Real Surprise

I am certainly finding the Front Range region to be exceptionally diverse when it comes to wasps, but nothing could have prepared me for what I found in the field yesterday, August 7. I was looking over a White Sweet Clover (isn’t there a song about that?), when a very large wasp commanded my attention. I immediately recognized it as a paper wasp, but not a species I would have expected in Colorado Springs.

This is a male specimen of Polistes carolina or Polistes perplexus. Either way, it is most likely going to turn out to be a county record, potentially a state record, and perhaps even a range extension. Both species are recorded for Kansas, so what is a couple hundred more miles or so?

I also managed to collect the specimen, so I’ll be able to eventually examine it under a microscope for the details necessary to separate the two species. Until very recently, it was thought that the males could not be distinguished at all, but apparently there are transverse (horizontal) ridges on the propodeum (hindmost segment of the thorax) that are weak in P. carolina and much more evident in P. perplexus. Watch this space for the final determination of the species.

For now, I’m ecstatic over this discovery. I’d sure like to find the nest this fellow came from. Females are a little easier to identify, and finding the nest would verify that this is a species breeding here. Even so, this male is in immaculate condition, suggesting it did not travel a long distance.

Because these two species were once thought to be a single species (P. carolina), most documentation of their biology is somewhat suspect. Polistes carolina apparently nests in exposed situations, such as under the eaves of buildings, for example; and reports of that species nesting in hollow trees and other protected locations actually apply to Polistes perplexus. Prey is probably similar in both species, consisting mostly of caterpillars chewed up by the adult wasps and fed to the larvae in the nest. Still, wasps this large can probably tackle much larger prey, and a single record of an attack on a cicada (Tibicen auletes) could be for either species of wasp.

I find that in current literature the size of these wasps is measured by the length of the forewing, which is 15-20.5 millimeters in P. carolina, and 17-21.5 millimeters in P. perplexus. Contrast this with the measurements of the abundant and widespread Northern Paper Wasp, Polistes fuscatus. Forewing length for that species averages between about 13 and 17 millimeters.

Polistes carolina is most common in the southern U.S., but ranges from New York, Pennsylvania, and Ohio south to Florida and west to Illinois, Kansas, Arkansas, and eastern Texas. There is one record for Ontario, Canada, but the species is not established there. That could be the case here in Colorado, too: a fluke. P. perplexus ranges from Maryland to Georgia, and west to southern Illinois, Kansas, Oklahoma, and Texas. One recent record has come from Pennsylvania.

Keep your own eyes open for species that seem “misplaced.” Interstate (and international) commerce, climate change, and other factors are changing the distribution patterns and abundance of many species. We also haven’t looked that closely at insect species with little or no economic impact. You stand a good chance of adding to our collective knowledge with relatively minimal effort.

Source: Buck, Matthias, Stephen A. Marshall, and David K.B. Cheung. 2008. “Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region,” Canadian Journal of Arthropod Identification No. 5: 492 pp (PDF version).

Wasp Wednesday: Polistes flavus

One of the most conspicuous wasps in the Sonoran Desert is the paper wasp Polistes flavus. This is a large wasp that frequents the same narrow belt as saguaro cacti, seldom being encountered at lower or higher elevations. Its large size, and almost entirely bright yellow color helps to separate this species from every other paper wasp in the region.

Little is known about P. flavus despite its relative, if seemingly localized, abundance. I have seen nests on only a handful of occasions, and they were all placed under the eaves of buildings. Unfortunately, those observations were made before I started taking digital images. I do recall that the nests were large, if only because the paper cells needed to accommodate these wasps have to be correspondingly large. Fortunately, my good friend Margarethe Brummermann did manage an image or two, one of which is shown below.

You are most likely to see these wasps in one of three situations: at water, at flowers, and perching on prominent vegetation. Worker females often congregate around receding waters of the intermittent streams characteristic of the Sonoran Desert. They may even land on the water, sprawling across the surface film and drinking deeply. They will visit swimming pools when natural sources are not available. Many other species of desert Polistes and Mischocyttarus will exhibit the same behavior. They all need water to manufacture saliva to mix with wood fibers to create the paper used in building their nests.

Paper wasps attack caterpillars and other insects to take back to the nest to feed the growing larvae, but the adult wasps need carbs, not protein. Consequently, paper wasps make use of flower nectar and “honeydew” from aphid colonies. Look for Polistes flavus on the blossoms of Seep Willow (Baccharis salicifolia) and, to a lesser degree, Desert Broom (Baccharis sarothroides). The wasp in the image below is on a Seep Willow.

Male paper wasps are often even larger than the females and therefore even more obvious and intimidating. This is especially true when they engage in territorial behavior, perching on prominent twigs or branches along the edges of dry riverbeds and other flyways. From these outposts the males scan for passing females and rival males. They will also chase away other insects, then return to their perch or another perch close by. Males do not have stingers, but are powerful enough to back up their threats.

How do you tell a male paper wasp from a female? Males have longer antennae, dramatically hooked at the tip, and their faces are more “square” than those of females. Males tend to have very pale faces, too. Females have shorter antennae, not as prominently hooked, and triangular faces that are usually darker.

One paper wasp likely to be confused with P. flavus is P. apachus, which is colored in yellow and reddish brown. P. apachus almost invariably has two parallel yellow stripes on the top of the thorax (see below), whereas that area is almost entirely yellow in P. flavus. Another confusing species is P. aurifer, which is entirely reddish brown on top of the thorax.

Look for P. flavus in Arizona, as well as southern California, Nevada, Utah, New Mexico, and western Texas. Males can easily overwinter in milder parts of that range, though they are normally more common in autumn as colonies prepare to suspend activities for the colder months.

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).