Wednesday, February 29, 2012

Wasp Wednesday: Not Wasp VII

Imagine one’s surprise at finding wasps suddenly appearing inside their home in the middle of winter. It is not impossible, as queen yellowjackets and some female paper wasps hibernate, overwintering inside houses and other human structures. They may stir if they find their way inside to heated rooms. However, other kinds of insects can be mistaken for wasps. I recently had occasion to identify one such masquerader.

One of the keepers at the Cheyenne Mountain Zoo here in Colorado Springs discovered wasp-like insects emerging from woody “perching material” used for birds in the African Rift Valley exhibit. To her credit she recognized them for what they really were: beetles.

These insects are black with yellow stripes, superficially resembling the markings of yellowjackets. They also run very rapidly, which enhances their resemblance to stinging insects. Many species of longhorned wood-boring beetles in the family Cerambycidae are convincing wasp mimics, and indeed that is what these specimens turned out to be. It was a bit more challenging to determine exactly which genus and species.

It helps to know what a beetle’s “host plant” is when trying to identify it. This only applies to herbivorous species, of course, but it is surprising how many vegetarian beetles feed on only a handful of different plant species. A variety of dead limbs from native hardwoods and conifers are used by zoo personnel for structural objects in exhibits, or as enrichment items to make life in captivity more humane and enjoyable for the animals. So, I knew the beetles were of local origin rather than something imported accidentally from overseas.

From my experiences in Oregon, I had my suspicions as to what genus this beetle belonged to: Neoclytus. There are 25 species in North America, so the next step was determining which ones are found in Colorado. Using a publication on Colorado Cerambycidae (Heffern, 1998), I learned that there are five, maybe six species of Neoclytus known from the Centennial State.

I was able to go online and look up images of the common Colorado Neoclytus species, and the only one to match the specimens given to me by the zookeeper was the Banded Ash Borer, Neoclytus caprea.

Although ash (Fraxinus spp.) is the favored host, the Banded Ash Borer is known to bore in a variety of dead and dying trees. Netleaf Hackberry (Celtis reticulara), hickory (Carya spp.), elm (Ulmnus spp.), oak (Quercus spp.), mesquite (Prosopis spp.), walnut (Juglans spp.), eucalyptus (Eucalyptus spp.), and grape (Vitis spp.) are all hosts to the wood-boring larval stage of this beetle. Trees weakened by drought, disease, fire, and attacks from other insects are especially vulnerable. Rarely are healthy trees attacked.

Adult beetles normally emerge in early spring. After mating, females lay eggs in bark crevices of the host tree. The larvae that hatch from the eggs tunnel just beneath the bark before boring into the sapwood where they feed for most of the summer. The larvae pupate in autumn and overwinter in that stage.

The adult beetles measure 8-17 millimeters, size being a function of the amount of nutrition received in the larval stage. This is a widespread species, found throughout the U.S. except for the Pacific coast. It also ranges into eastern Canada. Look for adults outdoors from March to June. They emerge on the early end of that spectrum in more southerly latitudes.

Ash logs felled in winter are especially prone to attack by the beetles in the following spring. Infested logs brought indoors for firewood may spawn an early emergence of the beetles due to the artificial warmth and extended “daylight” presented by indoor stimuli.

Milling of infested timber may actually prolong the life cycle of wood-boring beetle larvae that survive the process. Dry wood may offer less nutritional value to the grubs trapped within it, meaning that a normal yearly life cycle may be extended to several years in the case of the Banded Ash Borer.

The next time you find a swarm of “wasps” in your home, check the firewood first, and see if it might not be beetles like the Banded Ash Borer, the Hickory Borer, or a related species. Relax, they are at most a nuisance.

Sources: Heffern, D. J. 1998. “A survey of the Cerambycidae (Coleoptera), or longhorned beetles of Colorado,” Contributions of the C. P. Gillette Museum of Arthropod Diversity. Colorado State University: Department of Bioagricultural Sciences and Pest Management. 32 pp.
Karren, J. B. and Alan H. Roe. 2000. “Banded Ash Borer,” Fact Sheet 11, Utah State University Extension.
Yanega, Douglas. 1996. Field Guide to Northeastern Longhorned Beetles (Coleoptera: Cerambycidae). Champaign, Illinois: Illinois Natural History Survey Manual 6. 174 pp.

Sunday, February 26, 2012

Spider Sunday: Funnel-web Wolf Spiders

Just when you think you understand spiders, nature throws a wrench in the works to contradict the stereotypes. Wolf spiders in the family Lycosidae are supposed to be nomadic hunters, some of which live in burrows. Not so fast! Believe it or not, one genus, Sosippus, actually spins webs. I know!

If you live in the southern U.S., Mexico, or Central America, you cannot assume that all the thick, sheet-like webs with funnel-like retreats are made by the true funnelweb weavers of the family Agelenidae. Sosippus creates nearly identical snares, sprawling over cacti, agave, and palmetto, or sprouting from rock crevices.

The two spiders also bear a close superficial resemblance to each other. The key to distinguishing them is to look at the eye arrangement. Despite being web-builders, Sosippus shares the eye pattern typical of its hunting cousins: The two posterior median eyes are large and forward-facing, underscored by a row of four much smaller eyes. Two more eyes, the posterior laterals, flank the others. Agelenids have a more compact eye arrangement, with eyes of relatively equal size.

Six species of Sosippus occur in the U.S. The one shown here is S. californicus, which ranges from southern California to Arizona and south through Mexico to Costa Rica. I found it to be very common throughout southern Arizona. They are sizable spiders. Mature females measure from 14.7-17.6 mm (average 16.6) in body length, while males are 13.4-14.4 mm. The species is most abundant in riparian situations, living at the edges of stream corridors or wetland habitats.

One of the behavioral traits that Sosippus shares with other lycosids is the “portable egg sac.” Females tether their egg sac to their spinnerets until the spiderlings hatch. Spiderlings ride on their mother’s back until their next molt, then share her web, sometimes for months. In captivity, older spiders seem capable of coexisting in a confined space provided they are fed regularly. Maternal females of the species Sosippus floridanus have been observed feeding their spiderlings for several months (Brach, 1976). S. texanus is a recorded host for the mantisfly Mantispa sayi, which means the spider’s eggs are consumed by the larval mantispid (Rice and Peck, 1991)

Next time you visit the Sonoran Desert, or the forest hammocks in Florida, keep a lookout for funnel-web wolf spiders. You are sure to find these arachnids to be fascinating residents of these ecosystems.

Sources: Brach, Vincent. 1976. “Subsocial behavior in the funnel-web wolf spider Sosippus floridanus (Araneae: Lycosidae),” Fla Entomol 59(3): 225-229.
Brady, Allen R. 2007. “Sosippus revisited: Review of a web-building wolf spider genus from the Americas (Araneae: Lycosidae),” J. Arachnology 35: 54-83.
Rice, Marlin E. and William B. Peck. 1991. “Mantispa sayi (Neuroptera: Mantispidae) Parasitism on Spiders (Araneae) in Texas, with Observations on Oviposition and Larval Survivorship,” Ann. Entomol. Soc. Am. 84(1): 52-57.

Wednesday, February 22, 2012

Wasp Wednesday: Trimorus

I worked on the identification of wasp and ant specimens collected in pitfall trap samples in 2009 at the University of Massachusetts. This proved quite a challenge as most of the insects were well under five millimeters in length; and they represented many families I was unfamiliar with in terms of their diagnostic features and biology. Among the most abundant were tiny wasps of the genus Trimorus.

The specimens were from traps laid the previous year in watersheds in central Massachusetts. I was in the lab in Amherst putting them under a microscope and sorting and identifying them. My first impression of Trimorus was that I was looking at more than one genus, if not more than one family. The genus belongs in the subfamily Teleasinae, family Platygastridae. The wasps are sexually dimorphic (males look different from females) and polymorphic when it comes to wing length.

Once I learned that I was looking at one genus, if not one species, it was easy to identify them. Males have extremely long antennae of uniform width. Females, on the other hand, have short, clubbed antennae. Both genders can be fully winged, have wings reduced in size and non-functional, nearly wingless, or completely wingless (brachypterous). Nearly wingless individuals are actually “micropterous,” meaning the wings have been reduced to tiny flaps.

What was any kind of wasp doing in a pitfall trap, you ask? Pitfall traps are containers buried in the soil such that the opening is flush with the surface of the ground. A cover is usually placed over the trap to keep out rain and mimic a sheltering stone or board that a nocturnal animal would take refuge under during the day. Pitfall traps do not usually trap flying insects (unless baited with some kind of attractant). So, why would wasps be found in such a trap?

It turns out that at least most of the members of the subfamily Teleasinae are parasites of the eggs of ground beetles (Coleoptera: Carabidae). The female wasp lays her own egg inside the egg of the beetle. Not surprisingly, most ground beetle eggs are found on or in the soil. T. caraborum is recorded as an egg parasite of the ground beetle Chlaenius impunctifrons (Fouts, 1948).

These are truly minute insects, few if any exceeding two millimeters in length. Many are under a millimeter.

There are approximately 480 species worldwide in the Teleasinae, with 389 species of Trimorus known globally (Austin, 2005). This is probably only a small fraction of the total fauna, as many new species await description and/or discovery.

Up until recently, the Teleasinae was placed in the family Scelionidae. Molecular analysis led to the “demotion” of the Scelionidae to a subfamily itself.

The sheer diversity and abundance of Trimorus, and other members of the Teleasinae, point to their great importance in ecosystems. It would pay us to look a little more closely at the species close to our own homes. Who knows what discoveries await us?

Sources: Austin, A. D., N. F. Johnson, and M. Dowton. 2005. “Systematics, Evolution, and Biology of Scelionid and Platygastrid Wasps,” Annu Rev Entomol 50: 553-582.
Fouts, Robert M. 1948. “Parasitic wasps of the genus Trimorus in North America,” Proc U S Nat Mus 98(3225): 91-148.
Grissell, Eric. 2010. Bees, Wasps, and Ants: the indispensable role of Hymenoptera in gardens. Portland, Oregon: Timber Press. 335 pp.
Johnson, James B. 1995. Parasitoids of the Columbia River Basin. Interior Columbia Basin Ecosytem Management Project (contract # 43-0E00-4-9222).

Sunday, February 19, 2012

Spider Sunday: Featherlegged Orb-weavers

A surprising number of spider families spin the familiar wheel-like webs we see in our yards, gardens, and parks. While most orb webs you see are produced by “ecribellate” spiders that spin glue-studded silk to catch prey, some orbs are spun by “cribellate” spiders that use “hackled,” non-sticky threads to ensnare victims. The most common cribellate orb weavers in North America belong to the genus Uloborus, family Uloboridae. They are known as “featherlegged orb-weavers” for the tuft of hairs midway down each front leg that several species display. They are also called “hackled band orb-weavers.”

What exactly is a cribellate spider? Cribellate spiders possess two anatomical structures that ecribellate spiders do not. Chiefly, the cribellum is a plate-like organ on the underside of the spider’s abdomen just in front of the spinnerets. The cribellum produces a special type of silk that can be manipulated into a tangle of threads that snags prey as effectively as the sticky glue produced by ecribellate spiders. A cribellate spider also has a special row of bristles, called a calamistrum, on the outer surface of the metatarsus of each hind leg. This structure acts as a comb to fluff the cribellate silk into those tangled strands.

The Uloboridae also includes the triangle spiders I wrote about previously. These are very small arachnids. Mature Uloborus are only 3-6 millimeters in body length, males slightly smaller. Five species in the genus occur in North America, collectively distributed across the entire U.S. and southern Canada.

Webs of Uloborus are relatively small, usually horizontal orbs that may sport a stabilimentum (thickened, often zig-zag patterned band of silk). The stabilimentum may take the form of an auxiliary spiral, or a linear band running through the center of the web. The web shown above is one I discovered inside the greenhouse at the Tucson Botanical Gardens where the seasonal “Butterfly Magic” exhibit was in full swing. While the spiders cannot capture the large butterflies in such an exhibit, the silk can still incapacitate the insects and render them incapable of flying or feeding properly. I have also found featherlegged orb weavers at the mouth of culverts, and a variety of other outdoor situations.

Female Uloborus construct small, flattened, papery egg sacs (see image below, with recently hatched offspring). The egg sac is usually near the periphery of the web, and there can be several in a row.

The hatchlings build an orb web immediately after they disperse, but their webs differ greatly from those of more mature individuals. This is because they are born without their trademark attributes: a cribellum and a calamistrum. Consequently, the webs of recently hatched spiderlings have many additional radii (spokes), and the auxiliary spiral is retained at the hub (center). After its second molt, the spiderling is able to spin a “normal” web (Foelix, 2011).

There are competing theories on to whether orb webs evolved independently among cribellate and ecribellate spiders, or if the orb web came about only once. The convergent theory that proposed the orb web evolved twice held sway for many decades, but recent studies of spiders, and the molecular analysis of their silk, has now given weight to the assertion that the orb developed only once in the evolutionary history of spiders (Foelix, 2011).

These are truly remarkable arachnids. Remember that all members of the family Uloboridae lack venom glands, so are unable to quickly subdue prey by biting it. Instead, they kill by constriction. They wrap the victim so thoroughly that the silk binding compresses the softer body parts, and can even break antennae, legs, and other appendages. I suspect the silk may also shrink as it dries, further tightening around the insect until it dies of asphyxiation.

I leave you on that happy note to go seek for yourself the little wonders of the arachnid world around your own home and garden.

Sources: Foelix, Rainer F. 2011. Biology of Spiders (3rd Edition). Oxford: Oxford University Press. 419 pp.
Ubick, D., P. Paquin, P.E. Cushing, and V. Roth (eds). 2005. Spiders of North America: an identification manual. American Arachnological Society. 377 pp.

Wednesday, February 15, 2012

Wasp Wednesday: Poecilopompilus algidus

Here is a wasp that is still a wasp, but probably not the wasp you think it is. Did that make any sense? I know the first time I saw the spider wasp Poecilopompilus algidus, I thought it was a paper wasp (genus Polistes in the family Vespidae). Mimicry is not always a case of some defenseless organism looking and acting like a venomous, poisonous, or otherwise potentially dangerous animal.

Müllerian mimicry describes instances in which two or more species that are capable of defending themselves share a similar “look,” especially in color and pattern. Müllerian mimicry is named for German naturalist Fritz Müller, who first recognized this widespread survival tactic. Many well-armed species sport bold markings known as “aposematic” or “warning” colors.

I can attest from personal experience that Poecilopompilus spider wasps can back up their advertisement. The only specimen I collected of P. interruptus, in Cincinnati, Ohio, gave me a sting to remember! Ironically, the only other sting I recall with more vividness was from a Polistes aurifer paper wasp that I got when I was a careless child.

Poecilopompilus is a mostly tropical genus with only three representative species that reach the United States (P. flavopictus is recorded only in extreme southern Texas).

I just learned something new in researching this article. P. algidus has a much more widespread distribution in the U.S. than I had previously thought. It occurs from California to Arizona, Utah, Texas, Florida, and north to South Dakota, Minnesota and Michigan, even Massachusetts. Even more amazing, its mimicry is quite “plastic.” While in the south it tends to resemble a large paper wasp, in the north it may masquerade as another spider wasp in the genus Anoplius: Almost completely black with red bands on the top of the abdomen, as in this specimen. Not surprisingly, this insect is divided into at least four subspecies. The one I’ve imaged here is P. algidus coquilletti.

One cannot reliably use color patterns to even separate this species from P. interruptus, and equally widespread member of the genus. They key characters to look at instead are the spines on the front tarsi (“feet”) of females, and the inner margin of the eyes.

spines on front tarsi
inner eye margin
P. algidus3 strong spinesstrongly convergent at top
P. interruptus4 weak spinesparallel at top

The biology of these spider wasps is not especially well-known, though all are thought to prey exclusively upon orbweaver spiders in the family Araneidae. I have personally observed a female Poecilopompilus transporting a Western Spotted Orbweaver, Neoscona oaxacensis down a road in southern Arizona. My friend Margarethe Brummermann was able to document it here.

The female wasp stings her victim into weak paralysis and then hauls it backwards overland to a suitable nesting spot in bare soil. There she will deposit her burden, often in the crotch of a grass tussock or other vegetation, and begin excavating a shallow burrow. She may bite her way through hard soil, then kick the resulting crumbs beneath here with her front legs. The tunnels made by P. interruptus vary from 2.5 to eleven centimeters deep, angling from 45 to 90 degrees. The density of the soil might have an effect on depth. At the bottom is a spherical chamber where the prey is placed and a single egg laid upon it. Great care is then taken in filling and concealing the burrow entrance, the better to discourage potential parasites and predators.

One is most likely to see members of the genus Poecilopompilus on flowers, or on extrafloral nectaries of sunflower (Helianthus spp.). They are conspicuous insects in size as well as color, females of P. algidus coquilletti varying from 15-20 mm in body length, males 13-17 mm.

Sources: Evans, Howard E. 1949. “A taxonomic study of the nearctic spider wasps belonging to the tribe Pompilini (Hymenoptera: Pompilidae) Part I,” Trans Am Entomol Soc, vol. 75, no. 3/4: 133-270.
Evans, Howard E. and Carl M. Yoshimoto. 1962. “The Ecology and Nesting Behavior of the Pompilidae (Hymenoptera) of the Northeastern United States,” Misc Publ Entomol Soc Am 3(3): 67-119.
Kurczewski, Frank E. 1981. “Observations on the nesting behavior of spider-wasps in southern Florida (Hymenoptera: Pompilidae),” Fla Entomol, vol. 64, no. 3: 424-437.
Wasbauer, M. S. and L. S. Kimsey. 1985. “California Spider Wasps of the Subfamily Pompilinae (Hymenoptera: Pompilidae),” Bulletin of the California Insect Survey, vol. 26: 1-130.

Sunday, February 12, 2012

Spider Sunday: Western Spotted Orbweaver

It is winter now, and orb weavers (family Araneidae) are mostly spiderlings snuggled inside cozy silken egg sacs created by their mother. They will emerge when day-length is suitably long enough, and warmer weather more consistent, for prey animals to be more common. By late June, and into October, adult Arizona specimens of the Western Spotted Orbweaver, Neoscona oaxacensis, will be abundant, especially around wetlands and fields close to water.

This is by far the most common orb weaver I encountered while I lived in Tucson, and the Sweetwater Wetlands was a great spot to find them. The species occurs from Texas to Kansas, Illinois, and Indiana, and west to Colorado, Utah, Nevada, California, and eastern Washington state. It also ranges through Mexico and Central America to Peru. They are fairly large as adults, females 11-17 millimeters in body length, males 5-12 millimeters. No two specimens are alike, though, at least in color and pattern.

Much like each zebra has its own unique pattern of stripes, so, too, do individual N. oaxacensis spiders have their own individual pattern of spots, if it has spots at all. Note among the images shown here how variable the dorsal pattern on the abdomen can be. Interestingly, the ventral pattern (image below) is much more consistent and can help place the spiders to genus in places where there are other similar orb weavers.

One study in avocado orchards in San Diego County, California revealed that spiderlings begin emerging in the first week of March, with more emergences through April. The spiders then began decreasing in number from May until late October when few adults could be found. The adult spiders do not overwinter (Pascoe, 1980).

Male specimen

Repairing the web, feeding, and mating, are mostly early morning or nocturnal activities, though the spiders often occupy the hub (center) of their webs during the day, too. Sometimes a spider may retire to the periphery of its web, in some kind of retreat such as a curled leaf. This can be a common behavior in regions with intense midday heat and a lack of overhead shade from a tree canopy. The spider needs to avoid overheating and dehydration from the blazing sun. The retreat may be connected to the hub by a bundle of “signal threads,” but again this is uncommon for Neoscona.

Prey consists of flying insects, especially barklice, beetles, and moths. Webs usually stretch between vegetation at a height of 1.3-1.7 meters (4-5 feet) off the ground, though I have found them at lower levels. The prey-catching portion of the webs may span from 9 centimeters to over 39 centimeters ( 3.5-15 inches), varying according to the size of the spider. Younger spiders obviously spin smaller webs.

The Western Spotted Orbweaver can occasionally exhibit large, localized populations whereby the spiders can be exceedingly abundant in a small area (Allred, 1973). Do keep your eyes open for these wonderful arachnids. There are other common members of the genus Neoscona that can be found in eastern North America, too. More on those in later posts.

Sources: Allred, Dorald M. 1973. “An unusual population of spiders in Utah,” Great Basin Naturalist 33(1): 51-52.
Jackman, John A. 1997. A Field Guide to Spiders & Scorpions of Texas. Houston: Gulf Publishing Company. 201 pp.
Pascoe, Frank Henry. 1980. “A study of Neoscona oaxacensis (Araneae: Araneidae) in commercial avocado orchards in San Diego County, California,” Avocado Society Yearbook 1980 64: 153-186.