Friday, November 30, 2012

Holiday Gift Guide 2012

At this time of year I like to give a free plug to products that I have found useful myself, or that I believe would be beneficial to my readers and their friends. This year has seen a trio of books that I am proud to sing praises of. I even lent images and text to one of them. Enjoy!

Kollath+Stensaas Publishing continues to turn out highly useful, generously illustrated, and compact regional field guides on subjects seldom treated by major publishing houses. The latest from their presses is Insects of New England & New York, by Tom Murray.

Tom is a prolific photographer of invertebrates and his images here are more than worth the $18.95 retail price of the book. I was profoundly flattered to receive a free copy, but even more astounded to read the acknowledgements:

”When I was first becoming serious about insect photography, Eric Eaton….would regularly visit my website and identify my photos. With Eric’s encouragement I joined in March of 2005.”

Tom should be very proud of what he has done with that “encouragement.” Critics will say that the images of insects identified to species, or even genus, can be misleading to users trying to make their own identifications. This is true, because many species look essentially identical, or are conversely highly variable in color, pattern, and/or size. I would make the counter argument that one goal of a field guide should be to illustrate just how incredibly diverse invertebrates are. Tom and the publishers achieve this in boatloads.

Insects of New England & New York is more comprehensive than most field guides to insects for any region. It should be a standard reference for students of all ages throughout the northeast U.S. and adjacent southern Canada. Still can’t get enough of Tom’s photography? Then please visit his amazing galleries at

Another good friend, who I have yet to meet in person, had her own book come out this year. Seabrooke Leckie, together with David Beadle, produced the Peterson Field Guide to Moths of Northeastern North America (Houghton Mifflin Company).

Seabrooke lives in the wilds of Canada, assuring that any U.S. bias was curbed at least to some degree in the coverage of this book. Those that are familiar with Charles Covell’s A Field Guide to Moths of Eastern North America (Houghton Mifflin Company, 1984), also in the Peterson series, might think this new book to be redundant at best. Not true. Beadle and Leckie cover more species, and illustrate them with images of live specimens. No more pinned specimens with wings spread out. What you see at your porch light is what you will see in this book. Common variations in color and pattern are also shown for those species that vary in their appearance.

This book exceeded my expectations. One thing you might find puzzling, as I did, are the green, red, and orange bars next to the name of each species. Those bars represent “spring,” “summer,” and “fall” respectively. Beneath the bars is a black line that is not readily apparent, but which indicates the flight period for that species. This is explained in the “how to use this book” chapter, but it could have benefitted from a diagram. That is a minor negative, completely overwhelmed by the quality and comprehensiveness of this guide.

Seabrooke is a very gifted writer, and one’s style can be cramped by the constraints imposed by field guides. You owe it to yourself to visit her blog, The Marvelous in Nature, for a dose of her engaging style.

Last, but not least, Kenn and Kimberly Kaufman have another hit in the Kaufman Field Guide series with the Kaufman Field Guide to Nature of New England (Houghton Mifflin Company). Kenn was kind enough to approach me to contribute the terrestrial invertebrate section, both text and a few images, for which I was very grateful. Income never hurts, but it is always a joy to work with him on a new project.

Again, this book far exceeded my expectations, even though I should have known better. Yes, virtually every organism you are likely to encounter, plus geology, weather, and astronomy are covered in this book. From your backyard to the wilderness, it’s in there. Tidepool life, and open ocean fishes are even included. Wait, there’s more! You also get….passages on habitats, sustainability, endangered species, conservation, and invasive species. Now how much would you pay? Ahem. Sorry, I was momentarily channeling infomercials.

I am certain it is not coincidental that all three of these books are focused on New England or the northeast U.S. It makes sense for the publisher, as this is where the majority of the human population lives, recreates, and does business. I look forward to participating in the creation of more regional guides in the future. Breaking our biosphere down into bite-size regions means that you can cover more species.

There you have it, the three books that I think every naturalist should have on their shelves this year. Let me know your opinions, and feel free to make additional suggestions.

Wednesday, November 28, 2012

Wasp Wednesday: Carrot Wasps

Around the holidays, we humans tend to pack on the pounds as we indulge in feasts and parties at Thanksgiving and Christmas. Wasps do not have this problem. One family of wasps in particular manages to stay super-slim and slender: the Gasteruptiidae or “carrot wasps.”

There are at least fifteen species of carrot wasps in North America, all in the genus Gasteruption. Five of those occur in the eastern U.S. and Canada. At first glance, they might be mistaken for ichneumon wasps, or even sphecid wasps in the genus Ammophila. This is probably not coincidental, since carrot wasps do not sting, but could benefit by looking like other wasps that can sting.

You can easily identify carrot wasps by the following characters:

  • Pronounced “neck” between head and thorax.
  • Abdomen attached high up on the thorax, not between hind legs.
  • Hind tibiae swollen (think “leg warmers”).
  • Antennae with 13 segments (male) or 14 segments (female). Ichneumon wasps have far more antennal segments.
  • Ovipositor sometimes with a white tip
Species identification often hinges on the texture of various parts of the thorax; and to a lesser degree on color pattern.

These are not terribly large insects, from 13-40 millimeters depending on the species, and much of that length owing to the long ovipositor in females. They are so skinny they remind one of a flying needle.

The adult wasps are most often encountered at flowers, especially those umbelliferous blooms in the parsley family, hence their common name of “carrot wasps.” I have also seen them at White Sweet Clover (Melilotus alba) and Desert Broom (Baccharis sarothroides), and Leafy Spurge (Euphorbia esula). Flight activity seems to peak in late spring (latter half of May) and/or mid-summer (July).


The biology of gasteruptiids is rather poorly known, but so far our North American species appear to be parasites of solitary bees and wasps that nest in twigs or borings in wood. The female wasp needs her long ovipositor to reach the depths of a host’s tunnel and deposit an egg. The larval carrot wasp that hatches usually feeds on the pollen, nectar, or prey stored as food for the host larva, rather than the host larva itself.

Trap-nesting for solitary bees and wasps could easily reveal many more host records for Gasteruption wasps, if one keeps careful notes.

Sources: Jennings, John T. and Andrew R. Deans. 2006. “Gasteruptiidae,” The Tree of Life Web Project, Version 22.
Smith, David R. 1996. “Review of the Gasteruptiidae (Hymenoptera) of Eastern North America,” Proc. Entomol. Soc. Wash. 98(3): 491-499.
Townes, Henry. 1950. “The Nearctic Species of Gasteruptiidae (Hymenoptera),” Proc. U.S. Nat. Mus. 100(3259): 85-145 (Note that this reference includes what is now the family Aulacidae).

Sunday, November 25, 2012

Spider Sunday: Eastern Parson Spider

One of the more common and distinctive members of the family Gnaphosidae is the Eastern Parson Spider, Herpyllus ecclesiasticus. It gets its common name from the black and white color pattern that is reminiscent of the garb worn by old-time clergymen. It also sometimes makes house calls, which can be disconcerting to homeowners.

This species prowls mostly at night, and I find it fairly commonly around buildings, hoping to prey on small insects attracted to outdoor lights. It climbs well, so can be seen well off the ground.

By day, it hides under loose bark, or stones, boards, and other debris on the ground. Specimens that enter homes at night may seek refuge in clothing, shoes, and other objects. The spider may bite if trapped, but the effect of a bite depends mostly on the victim’s immune response. Rarely do symptoms exceed mild inflammation.

This is a mid-size spider, females ranging from 6.5-13 millimeters in body length. Males are 4.5-6.5 millimeters. The spinnerets are prominent in both genders, a characteristic of the family Gnaphosidae. Each spinneret is like a showerhead, with many tiny orifices through which silk is extruded.

The Eastern Parson Spider is widespread everywhere east of the Rocky Mountains, from southern Alberta across to Nova Scotia and south to Texas and Florida. West of the Rockies it is replaced by the Western Parson Spider, Herpyllus propinquus. Look for it in deciduous woodlands.

Mature specimens of this spider can be found year-round, suggesting it is fairly long-lived. Mated females spin an egg sac in autumn. The case is flat, and deposited in a silken retreat where the mother guards it. One egg sac in Connecticut, found under loose bark, contained 130 spiderlings.

Sources and Links: Aitchison, C.W. 1984. “Low-temperature Feeding by Winter-active Spiders,” J. Arachnol. 12: 297-305.
Cox, Shelly. 2011. “Eastern Parson’s Spider,” MObugs
Edwards, Robert L. and Eric H. 1997. “Behavior and Niche Selection by Mailbox Spiders,” J. Arachnol. 25: 20-30
Guarisco, Hank. 2007. “Checklist of Kansas Ground Spiders,” Kansas School Naturalist 55: 16 pp.
Minerva Webworks, LLC. 2012. “Eastern Parson Spider,” Sutton, Massachusetts,

Wednesday, November 21, 2012

Wasp Wednesday: Pepsis grossa

There are many species of “tarantula hawk” wasps in the western U.S., but the largest is Pepsis grossa, formerly known as Pepsis formosa. Interestingly, this insect exhibits both an orange-winged (xanthic) form, and a black-winged (melanic) morph. The two are almost never found together in the same location.

female xanthic form

My experience with P. grossa has been confined to southeast Arizona, but the species ranges from southern California and Nevada to Kansas, Texas, Arkansas, and Missouri. It also occurs throughout the Caribbean islands, Mexico, Central America, and northern South America. The xanthic form is found from Arizona north and east, and also in central Mexico. In southern Ecuador and northwest Peru, there is a “lygarochromic” variation whereby the wings are dark at the base, with a median patch of dark amber, and a pale wingtip.

These are enormous wasps impossible to overlook. Females average a whopping 43 millimeters in body length (30-51 mm). Males are smaller, 24-40 millimeters.

male melanic form

These giants can still be confused with the very similar, but smaller P. mexicana. Males of P. grossa can be distinguished by the fact that they have twelve antennal segments. No other Pepsis species has that number of segments. Females of P. grossa have long, coarse hairs beneath the femur of the front leg, though this feature can be abraded in older, worn specimens.

Females hunt for their tarantula prey mostly in the morning and evening to avoid overheating in the intense summer sun. Flying low over the ground, they may detect the presence of a tarantula burrow by sight or smell. Occupied tarantula burrows have a silk curtain over the entrance by day, and perhaps the wasp is tuned in to chemicals in the silk that indicate a spider is at home. The wasp may also land randomly and scour the soil on foot, flicking her wings and bobbing her antennae feverishly.

Once she does find a burrow with a spider inside, she cuts away the silk curtain and cautiously enters the burrow. Soon, both wasp and spider erupt from the burrow. This eviction behavior is crucial to the wasp’s success in securing her prey. She would have far less room to maneuver inside the spider’s tunnel.

The wasp steps back, grooms herself thoroughly, and then sizes up her adversary. She uses her antennae to entice the spider into raising itself off the ground; or even antagonizes the arachnid into a threat posture whereby the tarantula raises its front legs high, exposing its fangs. The wasp then seizes the second leg and thrusts her stinger between the base of its leg and its sternum. She strikes a nerve center in that location which causes the spider to become paralyzed.

The wasp may feed on fluid from the wound created by her stinger, or groom herself again before commencing the laborious procedure of carrying her prey away.

Tarantula hawks often simply drag their paralyzed burden into back into its old burrow, but on occasion they may dig another burrow and bury the spider there. I am pretty certain I witnessed the very end of this sequence one evening at Tohono Chul Park in northwest Tucson. The female shown below was busy filling a shallow depression by scraping sand into it.

female melanic form

The female lays a single egg on the tarantula and then seals the burrow. The larva that hatches from the egg will then consume the spider. Once finished, the larva will spin a silken cocoon, metamorphose into the pupal stage, and eventually emerge as an adult wasp sometime later.

Look for both male and female tarantula hawks on flowers, especially milkweeds (Asclepias spp.), where they fuel themselves on nectar. During the heat of midday, they will seek shelter amid foliage on trees and shrubs, sometimes gathering by the dozens on one plant. Males, and the odd female, may also spend the night in such aggregations.

Despite their intimidating size, these are rather placid animals unless provoked. An agitated tarantula hawk adopts a threat posture with wings splayed and abdomen curled under. They also secrete a strong, but not unpleasant, odor. Take heed! Stings from Pepsis are not life-threatening unless you are prone to allergies, but the pain is incredible. According to Justin Schmidt, you are in agony for about three minutes, and then it is pretty much over (the pain). Actual results may vary, so I am not volunteering to experiment any time soon. Neither should you.

Sources: Alcock, John. 2000. “The Tarantula Hawk Wasp’s Potent Sting Stuns and Kills the Much Larger Tarantula,” Arizona Highways, 76(10): 40-41.
Hurd, Paul David, Jr. 1952. “Revision of the Nearctic Species of the Pompilid Genus Pepsis (Hymenoptera, Pompilidae),” Bull. Am. Mus. Nat. Hist. 98(4): 261-334.
Punzo, Fred. 2007. “Interspecific Variation in Hunting Behavior of Pepsis grossa (Fabricius) and Pepsis thisbe Lucas (Hymenoptera: Pompilidae): A Field Study,” J. Hym. Res. 16(2): 297-310.
Schmidt, Justin O. 2004. “Venom and the Good Life in Tarantula Hawks (Hymenoptera: Pompilidae): How to Eat, Not be Eaten, and Live Long,” J. Kans. Entomol. Soc. 77(4): 402-413.
Vardy, C.R. 2002. “The New World tarantula-hawk wasp genus Pepsis Fabricius (Hymenoptera: Pompilidae) Part 2. The P. grossa- to P. deaurata-groups,” Zool. Verh. 337: 1-134.

Sunday, November 18, 2012

Spider Sunday: Hentz's Orbweaver

Some spiders simply cannot be ignored, and judging by the volume of images and questions we get over at, the most conspicuous spider of late summer and fall is one of the spotted orbweavers: Neoscona crucifera. Indeed, the spiders and their webs are very conspicuous.

This species was formerly named Neoscona hentzii, hence the common name. It is also known as the “Barn Spider,” but it unfortunately shares that name with another orbweaver, Araneus cavaticus. The two look similar in size, shape, and color. Neither species has a distinct pattern, but the markings on the underside are often more consistent, and a slightly better way to distinguish the two in the field.

Mature females of N. crucifera measure 9-20 millimeters in body length, while males range from 5-15 millimeters.

This is a widespread spider, found from Massachusetts to Minnesota, Nebraska, Colorado, and southern California, south to Florida and central Mexico. It favors moist woodland habitats, but can turn up in yards, gardens, parks, and even under the eaves of homes and other buildings. Outdoor lighting attracts insects at night, and many kinds of orb weavers seem to know this. So, they may stretch their webs across your front porch, garage door, or other convenient spot where they can intercept moths, flies, katydids, and other potential prey.

Immature N. crucifera build their webs only at night, taking them down at daybreak. By removing their webs they erase any obvious clue to their presence that birds or other predators may notice. The Black and Yellow Mud Dauber, Sceliphron caementarium, and the Organ-pipe Mud Dauber, Trypoxylon politum, are especially adept at finding orb weavers by following the framework of a web. Remember, the foundation lines of spider webs are not sticky, so can be navigated with impunity by both the spider and its predators alike. The cost of losing potential daytime prey captures pales compared to the benefit of remaining undetected by your own predators.

Adult females leave their webs up during the day, the owner hiding at the periphery of the snare in a curled leaf, or huddled on a twig.

She usually sits head-down in the center, or “hub,” at night. As insects become scarce in autumn, she needs to maximize her prey-catching opportunities, both day and night. The spider consumes a damaged web, recycling the silk.

Mature male orb weavers strike out in search of females and may be found wandering almost anywhere. Not only do adult males not bother spinning webs once they are sexually mature, but they actually lose the physical capacity to do so. They no longer manufacture the types of silk necessary to spin a web. All energy goes into finding a mate. The males mature faster than the females, so some may patiently wait in the vicinity of a female’s web until she becomes an adult.


Once mated, females prepare an egg sac, laying up to 1,000 eggs in a spherical or convex mass, covering it with a layer of fluffy, yellow silk, and usually concealing it in a rolled leaf. The sac measures only 5-12 millimeters in diameter.

Orb weavers in general are great to have around your home as they kill many insect pests. Their webs are glorious accomplishments of animal architecture; and the spiders themselves are harmless to people and pets, despite their sometimes intimidating size. Enjoy their beauty and presence before the killing frosts come.

Sources: Barnes, Jeffrey K. 2003. “Hentz’s Orbweaver,” University of Arkansas, Arthropod Museum Notes No. 23
Lapp, Joe. 2007. “The Intelligent Neoscona crucifera,”

Wednesday, November 14, 2012

Wasp Wednesday: Blue-winged Wasp

One of the most common solitary wasps of late summer and fall is a member of the family Scoliidae known as the “Blue-winged Wasp,” Scolia dubia. This is a fairly large insect, 20-25 millimeters in length, and easily identified by its bi-colored abdomen: Black on the upper half and red on the bottom half, with two bright yellow spots in the red area. There is rarely any variation in that color scheme, either. The common name stems from the brilliant blue highlights in the black wings that shine when sunlight hits them just right.

Scolia dubia is also a widespread species, found from Massachusetts to Florida, and west to Colorado, Arizona, and southern California. I have found them in New Jersey, Ohio, and Colorado. They are parasites of the grubs of scarab beetles, particularly the Green June Beetle, Cotinis nitida, and Japanese Beetles, Popilla japonica. Since Colorado has neither of these species, the Blue-winged Wasp must exploit a different host here. We certainly have plenty of May beetles (genus Phyllophaga), and the Bumble Flower Beetle (Euphoria inda), so I suspect those are the local hosts here in Colorado Springs.

The female wasp somehow divines the presence of beetle grubs underground while flying low over the surface of the soil in what approximates a figure-eight pattern. When she detects one, she lands, and sets about unearthing it. Scoliid wasps have strong legs that are heavily spined. This adaptation facilitates their digging activities.

An exposed scarab grub will writhe around and seek to rebury itself immediately. The wasp stings the larva to paralyze it and allow her to manipulate it. She may leave the grub in situ, or tunnel below it, excavating a small chamber where she deposits the beetle larva and lays an egg on it, perpendicular its body. She then seals the chamber and leaves to start the process all over again, often staying underground and digging her way to the next grub.

Interestingly, these wasps may sting several grubs without laying eggs on them. The paralysis of the beetle larva is usually permanent, so regardless of whether they become food for larval wasps, the beetle grubs are unable to complete their own life cycle. This is a good thing if you happen to have an infestation of “white grubs” in your lawn or garden.

Back to the egg on the beetle grub, though. The wasp larva that hatches feeds as an external parasite on the grub for one or two weeks before spinning a silken cocoon around itself. There it will remain as a pre-pupa for the winter, pupating the following summer and eventually emerging as an adult wasp.

Male and female scoliid wasps commonly visit flowers to feed on nectar (and perhaps pollen). I find them most often on White Sweet Clover, Melilotus alba, thoroughworts (genus Eupatorium), and goldenrod (Solidago spp.). Males can be identified by their long antennae and overall more slender appearance. Males have a distinctive, three-pronged “pseudostinger” that is part of their external genitalia. Males cannot sting, and females are loathe to sting unless physically molested.

Another interesting aspect of the males is their behavior. Males also fly near the ground in a sinuous pattern, hoping to detect virgin females emerging from the ground. This usually happens in the morning, and males abandon their searching by late afternoon. At that time, they may gather together to roost for the night on vegetation, as the image below depicts.

© Tim Moyer via

Keep an eye out for the Blue-winged Wasp in your own yard. Remember they are beneficial, but beware that large numbers of them may indicate you have a serious problem with white grubs.

Sources: Grissell, Edward E. 2007. “Scoliid Wasps of Florida, Campsomeris, Scolia, and Trielis spp. (Insecta: Hymenoptera: Scoliidae),” Featured Creatures, document EENY-409, Entomology and Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences (IFAS), University of Florida.
Rau, Phil and Nellie. 1918. Wasp Studies Afield. Princeton, NJ: Princeton University Press. 372 pp (Dover Edition).

Sunday, November 11, 2012

Spider Sunday: Starbellied Orbweaver

There is no shortage of the weird in the spider world, and I found one more example on our trip to Cape May, New Jersey on October 3, 2012. A series of posts linked with nylon rope provides a barrier along the dunes in Cape May Point State Park, and this fence was being utilized by one of the strangest of North American spiders, the Starbellied Orb Weaver, Acanthepeira stellata.

One of my friends on Flickr asked “Why is it star’bellied’ when it's star-butted? Is there more star-ness on its belly?” I have to agree with her. Maybe the person that first saw one described it from the ventral side. The pointy tubercles certainly show up well from both angles. The spikes probably help deter potential predators. Indeed, the abdomen is not as soft as it is in many other spiders.

Acanthepeira stellata is one of four North American species in the genus, collectively found from southeastern Canada south and west to southern California. This species in particular is known from southeast Canada to Florida, and west to Kansas and Arizona.

These are not terribly large spiders. Mature females measure only 7-15 millimeters in body length, males 5-8 millimeters. The shape of the abdomen is distinctive, making them easy to identify in the field. Indeed, fields and meadows with tall grasses and herbs are where I have found them. Most references indicate they prefer this kind of habitat as well, where they lash their webs to rather flimsy stalks and leaves. They are also fairly common in cotton fields and other crops in the southern Great Plains.

Starbellied spiderlings emerge from egg sacs in summer, and overwinter as immature or penultimate (one molt removed from adulthood) specimens. Adult females may be found from May to October, at least in Illinois (Moulder, 1992). Mature males can be seen from May to September. I found adults, or near-adults, in Cape May, and the one pictured at the top of the page appears to be “ballooning.” Ballooning is a dispersal strategy used by many young spiders to travel afar and stake out their own territories. A spiderling typically climbs to a high point, stands on tip-toe (“tip tarsus?”), and issues long strands of silk from its abdomen. These threads are caught by the wind, and when the spider lets go, it may be blown hundreds of feet, if not a mile or more. They can gain serious altitude, too. One baby A. stellata was captured at 1000 feet in the air over Tallulah, Louisiana on December 13, 1930 (Fitch, 1963).

These are orb weavers, and they spin the characteristic round webs of other members of the family Araneidae. The webs span about 6-10 inches, and are rarely more than four feet off the ground. The spider usually sits in the center (hub) of the web, head down, awaiting the impact of a prey insect. When disturbed, the spider invariably drops to the ground and feigns death, legs tucked close to the body. Among leaf litter and tangled grasses, it can virtually disappear until danger passes.

The Black and Yellow Mud Dauber, Sceliphron caementarium, is known to prey on Starbellied Orbweavers, paralyzing victims and stashing them in mud cells as food for its larval offspring.

Acanthepeira stellata itself preys mostly on nymphs (immature) of grasshoppers, plus other medium-sized insects. There is one record of an adult female preying upon an American Green Tree Frog, Hyla cinerea, but this is certainly not a routine event (Lockley, 1990).

Sources: Fitch, Henry S. 1963. Spiders of the University of Kansas Natural History Reservation and Rockefeller Experimental Tract. Lawrence, KS: University of Kansas Museum of Natural History, Misc. Publ. no. 33. 202 pp.
Gaddy, L.L. 2009. Spiders of the Carolinas. Duluth, MN: Kollath+Stensaas Publishing. 208 pp.
Lockley, T.C. 1990. “Predation on the green treefrog by the star-bellied orb weaver, Acanthepeira stellata (Araneae: Araneidae),” J. Arachnol. 18(3): 359.
Moulder, Bennett. 1992. A Guide to the Common Spiders of Illinois. Springfield, IL: Illinois State Museum Popular Science Series, vol. X. 125 pp.
Weber, Larry. 2003. Spiders of the North Woods. Duluth, MN: Kollath+Stensaas Publishing. 205 pp.

Wednesday, November 7, 2012

Wasp Wednesday: Purslane Sawflies

Not all wasps sting, and not all feed on other insects in their youth. The larvae of sawflies are vegetarians, and many are mistaken for caterpillars. You need not venture far to find sawflies, either. I found the adult female specimen below in my own backyard on the evening of September 18. Through a little detective work I discovered she is a Purslane Sawfly, Schizocerella pilicornis, in the family Argidae.

This species is unique among all argids (worldwide) in that its larvae feed internally on the host plant, mining inside the leaves of purslane. Until recently, it was thought that some larvae of S. pilicornis feed externally. Analysis of mitochondrial DNA has demonstrated that those leaf-nibbling larvae belong to a separate species, S. lineata (Hartsough, et al., 2007).

Adult females can be distinguished by the amount of black markings on the top of the otherwise red (or orange) thorax. Females of S. pilicornis have a solid, or nearly solid, black stripe down the center of the thorax, constricted in the middle. Females of S. lineate have very reduced black markings along the midline of the thorax. S. lineate is also slightly larger, females averaging about 7 millimeters to the 5-6 millimeter length of female S. pilicornis.

Both species are widespread in the New World, ranging from southern Canada to at least Central America. S. pilicornis occurs at least as far south as Argentina. U.S. records for S. pilicornis include Arizona, California, Colorado, Connecticut, Washington, DC, Florida, Indiana, Iowa, Kansas, Maine, Maryland, Michigan, Minnesota, Mississippi, Nebraska, New Hampshire, New Jersey, Ohio, Oregon, Texas, Virginia, and Washington. The species may actually be adventives here, and native to South America. At least, it was not described from North America until 1900.

Life history information may be open to debate since it comes prior to the realization that two species are involved (Gorske, et al., 1977). Females lay one egg per leaf, inserting the ovum into the foliage with the saw-like ovipositor that gives sawflies their common name. Larvae feed for roughly six days, going through five instars (an instar is the interval between molts). Mature larvae tunnel into the soil to a depth of about 3.5 centimeters where they pupate. Adults emerge a week later (during the summer generations; otherwise they overwinter as pupae). Their lifespan as adults is apparently very short, only 24 hours according to one source (Gorske & Hopen, 1976).

There can be up to six or seven generations annually, at least in Illinois, where these insects exert a small degree of biological control against purslane.

Males in this genus are easily identified by the last antennal segment, which is forked. It looks like the insect has four antennae instead of the two it should have.

I have found numerous males, and this one female, “sleeping” out in the open on grasses and other vegetation at sunset. Many wasps (and solitary bees) can be found by looking in fields and meadows for sleeping individuals at dusk, in the early morning, or during inclement weather.

Sources: Gorske, S.F. and H.J. Hopen. 1976. “Purslane sawfly (Schizocerella pilicornis) as a biological control agent of Common Purslane (Portulaca oleracea L.),” a paper presented at the 73rd annual meeting of the American Society for Horticultural Science, August, 1976.
Gorske, S.F., H.J. Hopen, and R. Randell. 1977. “Bionomics of the Purslane Sawfly Schizocerella pilicornis,” Ann. Entomol. Soc. Am. 70(1): 104-106.
Hartsough, Chester D.B., Edward F. Connor, David R. Smith, and Greg S. Spicer. 2007. “Systematics of Two Feeding Morphs of Schizocerella pilicornis (Hymenoptera: Argidae) and Recognition of Two Species,” Ann. Entomol. Soc. Am. 100(3): 375-380.

Sunday, November 4, 2012

Spider Sunday: A Common "Indoor" Spider

At this time of year, there is one spider that is commonly encountered indoors in the eastern United States and southeast Canada. It has a bi-colored body that makes it conspicuous and different from most other spiders one is likely to see around their residence. Trachelas tranquillus, is sometimes known as the “Broad-faced Sac Spider,” a member of the family Corinnidae.

This is a spider of average size, adult females measuring 7-10 millimeters in body length, males 5-6 millimeters. It occurs from Nova Scotia and Minnesota south to Kansas, Oklahoma, and northern Georgia, preferring deciduous woodlands. In nature, specimens are often found in retreats fashioned from curled leaves; or they are seen occasionally under stones.

I have seen this species hunting actively at night, prowling around porch lights where it may be hunting various insects attracted there. Trachelas does not spin a web, but does lay down draglines to help secure itself during climbs. Females probably also impregnate their draglines with pheromones (scents) so that males can track them down.

© Ken Lebo 2012

Mating usually happens in summer and early fall, after both genders have matured (nice images on the highlighted link). Females create a lens-shaped egg sac, the bottom flat against a substrate and the top slightly convex. The whole package is roughly ten millimeters long and usually attached beneath loose bark, or under a rock.

Besides killing live prey, Trachelas may scavenge on dead insects. Perhaps this is why it prospers when other spiders have either perished or gone into hiding in autumn. This scavenging habit may also influence the outcome in those rare instances when the spider bites a human. Secondary infections from its bite have been recorded, originally interpreted incorrectly as caused by the spider’s venom.

© Sarah Rose

The fact that Trachelas hunts regularly in and around homes and other buildings means it is more likely to have interaction with people. Still, verified cases of bites are infrequent, and usually result in only localized pain and swelling. People sensitive to arthropod venoms, or prone to allergic reactions, should seek medical attention for any arachnid bite (or sting in the case of scorpions).

Further complicating this picture is the confusion of Trachelas with another spider that is completely innocuous, though more intimidating. The Woodlouse Hunter, Dysdera crocata, is a specialized predator of woodlice, known commonly as “sowbugs,” “roly-polies,” or “pillbugs.” This species has exceptionally long jaws and fangs it uses to turn over its armored prey. While it looks dangerous, it is not.

Dysdera crocata © Nick Richter 2010

Dysdera is not native to North America, having been introduced from Europe at some point in our history. It has also become accustomed to prowling around human dwellings, so may be found indoors. It does not climb as well as Trachelas, however, and in my experience the Woodlouse Hunter prefers to hug baseboards.

Dysdera crocata © Sarah Rose

I encourage my readers to appreciate all spiders, but also act responsibly. It is a good idea to try and exclude spiders from entering your home and workplace by repairing worn weatherstripping on doors, mending holes in window screens, and sealing any cracks and crevices that could offer passage for insects and arachnids. Be careful when bringing objects indoors from outside, too, like firewood, gardening implements, children’s toys, and shoes and clothing left outdoors overnight.

Sources: Cox, Shelly. 2011. “Ground Sac Spider,” MoBugs blog.
Eaton, Eric R. and Amanda Howe. 2012. “Trachelas tranquillus (Ground Sac Spider),”
Jacobs, Steve. 2002. ”Broad-faced Sac Spider,” Penn State University fact sheet.