Wednesday, June 29, 2011

Wasp Wednesday: Not Wasp?

The beginning student of Hymenoptera (the order of bees, wasps and ants) cannot be blamed for misidentifying some members of the group, especially in the field where close-up and magnified views of the subject are impossible to obtain. The bees of the genus Nomada, for example, are easily mistaken for wasps.

The first time I encountered one of these “cuckoo bees,” I was convinced it was a “beewolf” wasp in the genus Philanthus. After all, there was a picture of Philanthus politus in Howard Evans’ wonderful book Wasp Farm that was a dead ringer for what I saw. Well, black-and-white photos don’t translate too well, and that species of beewolf does not occur in Oregon, where I saw my “wasp.”

There are more than 300 species of Nomada in North America. They are kleptoparasites of other solitary bees, meaning that their larvae feed on the pollen and nectar stored for the larvae of the host species. Members of the genera Andrena and Agapostemon are the common hosts for Nomada. Consequently, cuckoo bees are usually seen in the early spring, when Andrena bees are nesting. Watch for Nomada bees flying low over the ground in sunny openings in woodlands and along forest edges.

Because cuckoo bees exploit the hard work of the host bees, female Nomada have no “pollen baskets,” or dense brushes of pollen-collecting hairs on their bodies. They are quite naked, in fact, which adds to their wasp-like appearance.

Compare the bees in these images with the Cerceris wasps from last week. You may have a hard time telling the difference. I did, too. For a bit I was convinced I had images of a Nomada bee instead of a weevil wasp.

There is some consolation in the fact that our current scientific understanding of the phylogeny of bees and sphecoid wasps shows that the two groups are closely related. Sphecidae, Crabronidae, and all the bee families are now grouped under the superfamily Apoidea. Bees are apparently just wasps that at some point in their collective genetic lineages stopped hunting prey and started gathering pollen and nectar. Feel better now?

Sunday, June 26, 2011

Spider Sunday: Brown Widow

Spiders are very good at exploiting us humans, and using our vehicles and cargo to conquer new territory. One example of this phenomenon is the Brown Widow, Latrodectus geometricus. Exactly where this species is native to is a matter of speculation. It is known from South Africa, the Middle East (Afghanistan), the Mediterranean (Cyprus), Australia, the southern United States, and even Japan.

Here in the U.S., L. geometricus has been well-known in the southeast, but has been extending its range up the Atlantic Coast (to North Carolina so far) and across the entire southern tier of states (Tennessee, Texas, southern California). There have also been reports from Nevada and Colorado. The specimens shown here were imaged along a retaining wall at an undisclosed location in Redondo Beach, California (a friend’s house).

According to arachnologists, despite the virulence of the venom of the Brown Widow, the species should not be considered dangerously venomous to the average, healthy adult person. The spiders apparently inject less venom than black widows, and the effects are more localized than systemic. One can avoid the potential of a bite simply by not placing his or her extremities where they can’t see, and avoiding clutter in yards, sheds, garages, and other situations where the spiders are likely to occur.

The Brown Widow is very likely to be confused with a completely innocuous spider known as the American House Spider, Parasteatoda tepidariorum. The two are nearly identical in appearance, but the House Spider never has a red hourglass marking on the underside, whereas the Brown Widow does. Like most widows, the Brown Widow prefers to sequester itself deep inside cracks or crevices by day, venturing out into its web only at night. House spiders do not have retreats, so are visible at all times, though usually tucked snugly against a wall or other surface during the day. The House Spider also has a much broader distribution, being found across most of the North American continent. Below is a pair of House Spiders, male on the right.

The egg sacs of the Brown Widow are highly distinctive, being spherical but bearing numerous tufts of silk (see images below). Both the Brown Widow and the House Spider belong to the family of "cobweb weaver," Theridiidae, which only adds to the confusion in identifying them. They both build extensive, tangled snares.

The “spread” of the Brown Widow to the west coast is a relatively recent occurrence, the first specimens being noted in the Los Angeles area in February, 2003 as a result of the Los Angeles Spider Survey being conducted by the Natural History Museum of Los Angeles County. Verified accounts of this species from elsewhere along the Pacific Coast would be welcome. It has been suggested that trucks, cars, and recreational vehicles have mostly been responsible for the assisted migration of this species. That seems reasonable, especially in the case of RVs, which often sit idle for long periods, allowing spiders to establish themselves there.

Sources: Brown Widow Spiders
Santana, Fred. 2007. Brown Widow SpidersUF/IFAS Sarasota County Extension
Levi, Herbert W. and Lorna R. and Herbert S. Zim. 1990. Spiders and Their Kin. New York: Golden Books. 160 pp.

Wednesday, June 22, 2011

Wasp Wednesday: Cerceris sextoides

My recent trip to southern California in late May yielded some fine additions to my image database of wasps. One of the most photogenic species I encountered was a “weevil wasp,” Cerceris sextoides. These members of the family Crabronidae are known to hunt weevils and other beetles as food for their larval offspring. I didn’t find any females this time, though, only the territorial males.

Male solitary wasps tend to emerge before the females, the better to establish territories or seek out burrows where virgin females are likely to pop out. The male C. sextoides that I observed repeatedly perched on vegetation and maintained a vigilant eye for potential competitors. They would frequently fly out in pursuit of similarly-colored eumenid wasps, eventually resuming a perch, usually in a different spot. Some members of the genus are known to scent-mark stems and other objects to reinforce their territorial boundaries, but I am unaware if that applies to the males of this species.

Cerceris sextoides is a common wasp in the Pacific coast states, and extreme south-central British Columbia. It ranges inland through Idaho, northwest Utah, and northern Nevada. Look for it from May to October in a variety of life zones, from Lower Sonoran desert to high elevation Canadian.

The weevils Sitona californius and Trigonoscuta pilosa are recorded as prey for this wasp. Females ferret out their prey, paralyze it with their sting, and ferry it back to their burrow. Nests are typically excavated in sandy clay or gravelly clay. The horn-like process on the clypeus (“upper lip”) of the female probably assists her in digging.

Sources: Bohart, R. M. and A. S. Menke. 1976. Sphecid Wasps of the World. Berkeley, CA: University of California Press. 695 pp.
Bohart, R. M. and E. E. Grissell. 1975. “California Wasps of the Subfamily Philanthinae (Hymenoptera: Sphecidae).” Bulletin of the California Insect Survey. Vol. 19: 92 pp..

Sunday, June 19, 2011

Spider Sunday: Longlegged Sac Spiders

Some spiders seem to be much more common indoors than outside. Chief among those are the “longlegged sac spiders” in the genus Cheiracanthium. They belong to the family Miturgidae, known collectively as “prowling spiders,” but they were once classified in the sac spider family Clubionidae.

Indeed, telling Cheiracanthium from Clubiona is not at all easy. Cheiracanthium lacks a distinct groove in the center of its carapace (the top portion of the cephalothorax), and there is no obvious tuft of curved setae (hairs) on the front edge of the abdomen. Clubiona does possess those characters. More to the point, you are not as likely to find Clubiona indoors.

The sac spiders are named for the silken retreats they spin. They do not construct silken snares like many spiders, but hunt “on foot” for small insects they can simply overpower. Their tarsal claw tufts, composed of densely-packed hairs, help them grip even slick surfaces. They easily run across the ceiling, defying gravity and giving the average homeowner the heebie-jeebies.

Cheiracanthium are mostly nocturnal, so you are likely to find them resting during the day, inside those retreats. Look for their “sleeping bags” at the juncture of a wall and the ceiling. They seldom, if ever, reuse a retreat, so you may find more than one. Females also deposit their eggs in a sac within a retreat, and the spiderlings that hatch may return to the retreat after minor explorations. The spiderlings will disperse after their next molt, though.

Because these spiders usually stick to the higher reaches of the average house, they don’t often come into contact with the human occupants. All the same, there has been a good deal of historic controversy as to whether longlegged sac spiders are dangerously venomous. Rumors of necrotic bites similar to those sometimes caused by recluse spider bites have largely been put to rest.

Spider bites in general are very rare events, contrary to what you might think from media sensationalism and internet exaggerations. One truly serious threat that is understated or omitted in the discussion of spider bites is the possibility of secondary infection that can turn any minor puncture wound into something much, much worse. Always flush any kind of abrasion or wound thoroughly with potable water. Use antibiotic ointments at your discretion, bearing in mind that overuse of antibiotics has contributed to the rise of “superbugs” that are increasingly resistant to the drugs we throw at them.

Back to the spiders at hand. There are two species of Cheiracanthium in North America, known commonly as “yellow sac spiders” or “agrarian sac spiders.” C. inclusum, is native to the U.S. and occurs coast to coast except the northernmost states. C. mildei is native to Europe but was introduced to North America decades ago. It now has a very widespread distribution in the states, including New England and Washington state. This is the species most often encountered indoors. Both species are medium-sized, the body length of mature individuals varying from 4-10 millimeters, males on the smaller end of the spectrum.

Mature and penultimate males (specimens that have only one molt remaining before adulthood) can be recognized by a “leggier” appearance and the modified pedipalps that make the spider look like it is wearing boxing gloves (see image above).

There are some very good internet resources on this genus of spiders, including this fact sheet from Penn State University, and this one from Washington State University. Do go offline, though, and see if you can’t find one of these spiders in your own home, or possibly empty retreats that the spiders once occupied.

Wednesday, June 15, 2011

Wasp Wednesday: Brachymeria

Most wasps, and all insects for that matter, are under ten millimeters in length. They are quite literally The Smaller Majority, to quote the title of Piotr Naskrecki’s remarkable book. Among those most easily overlooked species are the parasitic wasps in the family Chalcididae. Chalcids are heavily-armored, mostly compact insects with “thunder thighs” on their hind legs. The hind femora are greatly swollen and the hind tibiae bowed to fit the curvature of the preceding leg segment. This anatomical attribute helps them to quickly jump away from danger and take flight.

Meet the genus Brachymeria, with 26 species known for North America. These 3-6 mm wasps are not uncommon primary and secondary parasites of the larvae of Lepidoptera and muscoid flies. The wasps emerge from the pupae of their hosts. Some species have been reared from grasshoppers as well, but probably as parasites of tachinid or sarcophagid flies that were themselves parasites of the grasshoppers.

I have found the adult wasps in the vicinity of aphid colonies, lapping “honeydew,” the sugary liquid waste products secreted by aphids. Here in Arizona I also find them seeking shade in the heat of the day, often among cattails or on shaded cottonwood leaves near artificial wetlands. The occasionally visit flowers as well, such as wild carrot, Daucus carota. Sometimes, an individual wasp will “play possum,” hugging its legs to its body and remaining motionless when disturbed.

According to accounts of the life cycle of Brachymeria fonscolombei, a common, holarctic species, female wasps use their ovipositors to inject eggs into the host larva. While more than one egg may be deposited in a host, eventually only one larval offspring will mature and emerge from the host pupa. The total developmental period from hatching of the egg to adult wasp emerging is about 20-27 days during favorable weather conditions. An overwintering generation can take approximately 155-180 days to complete its life cycle.

It is quite possible that Brachymeria fonscolombei is an important agent in limiting the numbers of blow flies and flesh flies that infest small animal carcasses. Likewise, other species are probably important in the regulation of other pest flies, and pest caterpillars.

Sources: Burks, B. D. 1936. “The Illinois Species of Brachymeria (Hymenoptera: Chalcididae),” Papers in Zoology. Illinois Natural History Survey: pp 251-254.
Roberts, Raiford A. 1933. “Biology of Brachymeria fonscolombei(Dufour), a Hymenopterous Parasite of Blowfly Larvae,” Technical Bulletin No. 365, United States Department of Agriculture. 22 pp. (this resource is likewise available online).

Sunday, June 12, 2011

Spider Sunday: Silver Argiope

I have no idea just how “regular” this feature will be, but I do have plenty of spider stories to tell, more than a year’s worth already. My involvement with the website SpiderIdentification.org has shown me just how much I have yet to learn about these amazing arachnids. Why not start out with a really spectacular species, then? The Silver Argiope, Argiope argentata certainly fills the bill.

Kim Moore, a nature photographer in Long Beach, California was kind enough to introduce this species to me last month at Bolsa Chica Ecological Reserve in Huntington Beach. I was surprised when she told me she usually sees the adult spiders about the same time as the Great Blue Heron chicks in the spring. Every other species of Argiope that I am familiar with does not mature until late summer.

Kim quickly found one amid a large patch of prickly-pear cacti on a steep embankment above the tidal marsh….then another….and another. There had to have been hundreds of them, and most of them mature females and males. They hung in the center of their orb webs the weight of the females warping the plane of their webs a bit.

The males look nothing like their mates. They are vastly smaller for one thing, only 4-5 mm in body length compared to the female’s 12-16 mm length. Males are also not as brightly colored. Some were already paired up with females when we found them.

This species is known to range from southern Florida to southern California. According to Mandy Howe, my comrade at SpiderIdentification.org, adults of Argiope argentata can be found at almost any time of year. Males mature very quickly, as early as February and as late as June. Mandy cites a paper by Herbert W. Levi that suggests this species may not be “annual” like the other members of the genus that range farther north.

The web is a characteristic “orb” web, round with radiating spokes and a spiral of sticky threads. The central “hub” is where the spider sits, her abdomen tipped back away from the plane of the web (except, I observed, when closely approached: then she plasters her abdomen against the hub).

The genus Argiope typically incorporates a zigzag band of silk down the middle of the web. This decoration is called a stabilimentum, and its function is the subject of continuing debate. It may act as an advertisement to prevent birds from tearing through the web, but a more likely theory is that it is a fake flower designed to attract pollinating insects. Indeed, the thick band of silk reflects ultraviolet light much as many flower petals do.

While other Argiope species generally have only a vertical stabilimentum, the Silver Argiope usually employs an X-shaped version. The female spider aligns two pairs of legs with each of the silk bands. Her own silvery body also reflects UV light, perhaps turning her into the perfect faux blossom. Oddly, the population at Bolsa Chica seems to have eschewed the silken “X” in their webs. I observed no decorative silk at all.

Keep an eye out for these if you find yourself in the geographic range of this arachnid. It is certainly hard to beat as one of the most ornate spiders in North America.

Sources: Kaston, B. J. 1980. How to Know the Spiders (Third Edition). Dubuque, Iowa: Wm. C. Brown Company Publishers. 272 pp.
Levi, Herbert W. 1968. “The spider genera Gea and Argiope in America (Araneae: Araneidae),” Bull. Mus. Comp. Zool. Harvard 136: 319-352 (cited by Mandy Howe).

Wednesday, June 8, 2011

Wasp Wednesday: Bristly Rose Slug

Wasps are sometimes named after their larvae. This is certainly true of many of the common sawflies in the family Tenthredinidae. Case in point: the “Bristly Rose Slug,” Cladius difformis. True to its epithet, the larvae of this insect are covered in tiny setae (hairs) and feed voraciously on roses. I was lucky enough to document both the adult and immature stages in a friend’s garden in Redondo Beach, California last month.

I spotted the adult female wasp on the morning of May 16 as she basked in the sun and groomed herself on a leaf adjacent to a rose bush. This is not a large insect, only about 6 mm in body length.

A male then suddenly appeared, and just as suddenly they were copulating. Note the sexual dimorphism, especially in the antennae of the male. This branching type of antenna is termed “pectinate” and is not uncommon in some wasps and beetles. The couple soon became unhitched and the male went his merry way.

The female wasp, had I been able to follow her long enough, would have laid her eggs in a rose leaf. She uses her saw-like ovipositor (hence the common name of the family) to cut into the upper surface of the midrib vein and create a pocket where she will deposit a single egg. The process is repeated several times on the same leaf. The ovipositor is a complex arrangement of a “lance” and at least one pair of “lancets,” all normally concealed inside a blade-like sheath when not being deployed. The lancets act in concert to cut through the leaf tissue, braced by the lance.

The tiny larvae that emerge from the egg begin to skeletonize small portions of the leaf. The larvae go through five instars (periods between molts), and their appetites seem to increase with each molt. Eventually they are creating enormous holes in the rose leaves.

I found several larger larvae (12-13 mm, nearly mature) on May 23. Their resemblance to caterpillars is obvious, but they have more pairs of prolegs (“false legs” that run the length of the abdomen) than do larvae of moths and butterflies (which have five or fewer pairs of prolegs). It is easy to see why this insect is considered a garden pest, given the heavy damage it can inflict. It is also known to feed on raspberries and strawberries. The larvae eventually pupate in a papery cocoon.

It is assumed that the Bristly Rose Slug was introduced to North America from northern Europe. Many authorities in fact synonymize Cladius difformis with Cladius pectinicornis of the Old World. David R. Smith, a renowned expert on sawflies here in North America, asserts that the two are distinctly separate species. The Bristly Rose Slug occurs on both coasts of North America, and from Nova Scotia to British Columbia. It seems to range only through the northern third of the United States except for the coastlines.

There are not many options available for control of this species, so handpicking the larvae off of leaves may be your best bet. The biological control “Bt” (Bacillus thuringiensis) is not effective.

There is more information, and more images, available online, of course, including the complete life cycle in images here.

Tuesday, June 7, 2011

More posts at Sense of Misplaced

Looking for a nature fix? Remember that I also run the blog Sense of Misplaced. I have added posts there documenting some of the places I traveled to in southern California last month, and more will follow. It is a busy time for me, and I'll be traveling again soon, so your patience with the Bug Eric blog is appreciated. Thank you.

Wednesday, June 1, 2011

Wasp Wednesday: Podalonia

A friend recently asked if I might be able to identify a wasp from images taken by a third person. That person, Jeffry B. Mitton, was then kind enough to grant permission to use his images to complement my own photographic documentation of the “cutworm wasps,” genus Podalonia.

These slender, thread-waisted wasps are frequently mistaken for other members of the family Sphecidae. Females look like small Sphex species, while males are easily confused with Ammophila wasps. Podalonia and Ammophila both belong to the subfamily Ammophilinae in fact. There are nineteen species known in North America, but the genus also occurs in Central America, Eurasia, and Africa. Identification of the species hinges on minute characters like the presence or absence of arolia (tiny pads between the claws on each “foot”), so images of live, wild wasps rarely suffice for species determination.

Cutworm wasps are named for the habit of the solitary females to hunt for soil-dwelling caterpillars (“cutworms”), paralyze them, and store them as food for the wasp’s offspring. The wasp digs her burrow after she procures the prey, which is the opposite behavior sequence of most wasps in the Sphecidae family. Only one caterpillar goes in the bottom of each burrow, and a single egg is laid upon it. The opening of the tunnel is then sealed and the wasp begins seeking another victim to repeat the process. I have yet to photograph one of these wasps with a caterpillar, but that is what Jeff Mitton did. Unfortunately, I do not know how to save those images from the e-mail to my computer. So, here is an image from Kim Moore instead.

Another phenomenon I have not witnessed is the nightly aggregation of some species in sheltered spaces. Ironically, I was on a field trip with an entomology class from El Camino College on the weekend of May 21-22 when one of the students discovered a gathering of female Podalonia under bark on a Ponderosa Pine stump. This was at the James Reserve in the San Jacinto Mountains of southern California. Several specimens of the wasps were collected before I learned of the find, and a return to the stump revealed no specimens present. Males also aggregate, as confirmed by this image. Several hundred individuals can pack together in such clusters. This behavior is thought to correlate with inclement weather, and possibly overwintering in the case of females, but perhaps it is a more common occurrence.

Mating is something these wasps seem to do quite frequently, judging by my own images. Males are on top. Both genders enjoy sipping flower nectar, and sometimes they satisfy their thirst and sex drive at the same time.

Podalonia are most abundant in the western United States, but you should be on the lookout for them almost anywhere. They are certainly welcome allies in the garden and agricultural field where they can dispatch a good number of pest caterpillars. Meanwhile, you can find videos of some of the European species in action on YouTube.com and Wildlife Insight.

Sources: Kurczewski, Frank E., Mark F. O’Brien, and Margery G. Spoffford. 1992. “Nesting Behavior of Podalonia robusta (Cresson) (Hymenoptera: Sphecidae),” J. Hym. Res. 1(1): pp. 235-239.
Murray, William Donald. 1940. “Podalonia (Hymenoptera: Sphecidae) of North and Central America,” Entomologica Americana Vol. XX, Nos. 1 & 2: pp. 1-82.
O’Brien, Mark F. and Frank E. Kurczewski. 1982. “Ethology and Overwintering of Podalonia luctuosa (Hymenoptera: Sphecidae),” The Great Lakes Entomologist Vol. 15, No. 4: pp. 261-275.