Candystripe Spider

Our most familiar cobweb weavers, like the Common House Spider and black widow, seem most abundant in or around buildings, so it might come as a surprise to learn that many, if not most, members of the family Theridiidae live outdoors in the strictest sense. One of the larger “wild” cobweb spiders is the Candystripe Spider, Enoplognatha ovata. It is also known as the “Polymorphic Spider” because it has several color variations.

This species is probably native to Eurasia, introduced to North America long ago. It is now a very common spider in New England, the Great Lakes region, and the Pacific states inland to Montana and Utah. They spin their tangled snares in understory vegetation in woodlands, and among wildflowers and herbs in meadows and fields. The spiders usually hide by day under a curled leaf. Females guard a white or bluish egg sac in late summer.

Individual specimens vary from entirely white, cream, or yellow in color with or without parallel rows of black spots on the abdomen, to having paired red stripes down the back, or even a broad central red stripe. Adult females measure 4.3-7 millimeters in body length. Mature males, 3.5-5.2 millimeters, are distinguished from females by their modified pedipalps and the elongated jaws (chelicerae).

Male

Spiderlings emerge from egg sacs in autumn, and overwinter in leaf litter and other protected niches on the ground. As they grow they are subject to parasitism by larval mites (ironically, mites are also arachnids) of the families Trombidiidae and Erythraeidae (Reillo, 1989).

I vividly recall finding this species commonly during my childhood in Portland, Oregon. Years later I found more during a visit to various forest preserves in suburban Chicago, Illinois. I find it interesting how some species are emblematic of one’s life and interests, be it birds, reptiles, or insects and spiders.

Sources: Reillo, Paul R. 1989. “Mite Parasitism of the Polymorphic Spider, Enoplognatha ovata (Araneae, Theridiidae), from Coastal Maine,” J. Arachnol. 17: 246-249.
Sollfors, Stefan. 2008. “Enoplognatha ovata,” Eurospiders.com.
Anonymous. 2013. “Comb-footed Spider, Enoplognatha ovata,” NatureSpot.

Forestflies (Spring Stoneflies)

Ever since we decriminalized the sale of marijuana in Colorado, people here seem to think that “stonefly” is a term that describes an insect trapped in a bong. That would be a stoned fly. Anglers know the difference, and right now is the time for “hatches” of spring stoneflies in the family Nemouridae along the Front Range.

The species I find most commonly probably belong to the genus Zapada, known as “forestflies.” I haven’t bothered to catch any specimens and turn them over. The cervical (“neck”) gills of the larval stage (nymph or naiad) are retained by the adult and are diagnostic. Two sets of branched gills on each side of the body mean it is in the genus Zapada.

© Arlo Pelegrin via Bugguide.net

Stoneflies in general are excellent indicators of water quality in streams and rivers because they are more sensitive to pollution, dredging, and other alterations to their habitat than many other aquatic insects. Spring stoneflies, which are also known as “little brown stoneflies,” are tolerant of a moderate amount of pollution and other human disturbance.

© J. Bodenham in Ward & Kondratieff, 1992

Nymphs of Zapada cling to submerged rocks and other heavy objects in flowing waters. There is one generation per year for the common species Z. cinctipes, meaning it is “univoltine.” Some other species require 2-3 years to complete their life cycle. The nymphs feed on vegetable matter, mostly leaves that fall into the water. Aquatic insects that chew up leaves are known as “shredders.”

© Tim Loh via Bugguide.net

Adult forestflies can begin emerging as early as late February, but most have their peak emergence from mid-March to mid-April. Mature nymphs, and adults, measure only 5-8 millimeters in body length (not including the wings of the adult), so these are not conspicuous insects. Adults are most often seen on bridges or logs that stretch across streams and creeks. They are quite active, running rapidly and flying when startled.

Considering the rich history of mining in the Pikes Peak region, and various chemical spills that have contaminated the few creeks and rivers here in Colorado Springs, I am rather surprised that forestflies continue to prosper.

Sources: Adams, Jeff and Mace Vaughan. 2003. Macroinvertebrates of the Pacific Northwest: A Field Guide. Portland, Oregon: The Xerces Society. 16 pp.
Brown, Wendy S. 2005. “Plecoptera of Gunnison County, Colorado,” The Aquatic Insects of Gunnison County, Colorado.
Stewart, Kenneth W. and Bill P. Stark. 1993. Nymphs of North American Stonefly Genera (Plecoptera). Denton, Texas: University of North Texas Press. 460 pp.
Ward, J.V. and B.C. Kondratieff. 1992. An Illustrated Guide to the Mountain Stream Insects of Colorado. Niwot, Colorado: University Press of Colorado. 191 pp.

Spring White

Fashion rules dictate that one cannot where white after Labor Day, but the Spring White butterfly, Pontia sisymbrii, need never worry. These pale insects expire long before that arbitrary deadline. Indeed, these are among the first butterflies of spring here along the Colorado Front Range, often appearing before the official date of the spring equinox.

Heidi and I have seen several specimens already this year, on March 9, along the Arkansas River below Pueblo Reservoir. I expect to see them any day now here in Colorado Springs.

These are wary butterflies that perch frequently but startle easily. Approaching one to take its photograph is usually an exercise in futility. Males are known to “hilltop,” flying along the tops of ridges and buttes to intercept females flying up from below. You can also find them in canyon bottoms, the topography funneling females into those areas.

Like most members of the family Pieridae, caterpillars of the Spring White feed on cruciferous plants: mustards and their cousins. Females deposit one egg at a time on the stems and foliage of host plants, especially hedge mustards (Sisymbrium spp.), tansy-mustard (Descurainia spp.), and rock-cresses (Arabis spp.). In some places in northern California, Brewer’s Jewelflower, Streptanthus breweri, produces orange spots that mimic the eggs of the butterfly. The female insect avoids those plants, since caterpillars are known to cannibalize each other when too many are on one plant (Pyle, 2002).

The caterpillars hatch from the eggs in roughly a week and begin feeding in earnest. The larvae progress through five instars (an instar is the interval between molts, first instar being what emerges from the egg), and older caterpillars are quite attractive as you can see in the image below, shot by Aaron Schusteff and borrowed from Bugguide.net

© Aaron Schusteff via Bugguide.net

At the end of the fifth instar, the caterpillar graduates to the pupa stage. The chrysalis is described as being mottled brown or black with a granular texture. While the chrysalids of most pierids are each suspended in a “girdle,” a belt-like strand of silk around the midsection and attached to the substrate at two points, the Spring White pupa lacks this feature. It attaches to the surface of the leaf, stem, or other object only at the tail end of its body. Hooks fasten into a tiny pad of silk to secure it firmly.

Some specimens have a nearly pure white upper surface

This butterfly ranges over most of the U.S. west of the Rocky Mountains, including the mountains of Arizona and New Mexico, spilling over the divide into extreme western South Dakota and the panhandle of Nebraska. It also occurs in south-central British Columbia. In Oregon and Washington it is found east of the Cascade range (and in the mountains of the Olympic peninsula in Washington).

Look for this species early in the season, from late February on through the end of June. It frequents foothills and higher elevations. It flies earlier than most whites, but pay attention to the dark pattern of veins on the underside of the hind wings to cinch an identification.

The Spring White may be a more accurate predictor of the arrival of spring than Punxsutawney Phil, the famed groundhog, at least here in the western U.S. Good luck getting the butterfly to pose for a photo opp, though.

Sources: Brock, Jim P. and Kenn Kaufman. 2003. Kaufman Field Guide to Butterflies of North America. Boston: Houghton Mifflin Company. 384 pp.
Lotts, Kelly and Thomas Naberhaus, coordinators. 2014. “Spring White,” Butterflies and Moths of North America.
Pyle, Robert Michael. 2002. The Butterflies of Cascadia. Seattle: Seattle Audubon Society. 420 pp.

Snail-killing Flies, genus Sepedon

You never know where learning the life cycle of an insect will take you; or how it might advance prevention of parasitic diseases on another continent. In this special procrastination edition of “Fly Day Friday,” we take a look at the fascinating fly genus Sepedon in the marsh fly family Sciomyzidae.

I was reminded of the strange lives of marsh flies when Heidi spotted one while we were walking our dog on an urban trail beside Fountain Creek in south Colorado Springs on February 24 of this year. I was surprised to see a specimen of Sepedon this early in the year, but there it was (image above).

There are twenty species of Sepedon currently recognized in North America (Knutson and Orth, 2001). These species are arranged in “species groups,” based on shared characteristics.

What is truly captivating is not the taxonomy (classification) of these flies, but their life cycle. The larvae of all Sepedon species are predators of aquatic pulmonate snails. These are air-breathing mollusks that have a simple lung in addition to, or instead of, gills.

Killing and eating snails is not without its risks. The fly larvae live just beneath the surface of the water, suspended by water-resistant hairs surrounding their posterior spiracles (breathing holes). The snails attacked are species without an operculum, the hardened plate that can seal the animal firmly inside its shell. So, a predatory fly larva won’t have the door slammed in its face when launching an attack. Still, the maggot can become suffocated by mucous excreted by the snail in self-defense; and the water-repellent hairs on the larva can get enmeshed in snail feces (Maharaj, et al., 1992).

Despite such perils, the fly larvae are efficient predators. Different lab studies have shown the larvae of different species can consume, individually, anywhere from eight to nearly fifty snails. Granted, many victims are very small. Indeed, the successful completion of a Sepedon life cycle depends on the availability of juvenile mollusks as prey for the first and second instars (an instar is the interval between molts). The third (and final) instar larva can take substantially larger snails.

Sepedon larva (A); posterior spiracles (B); anterior segments (C) ©Valley City State University, North Dakota

In the tropics, some aquatic snails are hosts of parasites, particularly schistosomes that can affect humans directly, and livestock liver flukes. Consequently, control of these snails is desirable. The possibility of employing snail-killing flies as biocontrol agents has been pursued with some vigor, but the few field trials have yielded mixed results.

Once a larva matures, it pupates. The puparium is capsule-like and boat-shaped, upturned at the posterior end, the better to float amidst organic matter at the margins of ponds or the shores of flowing waters. An adult fly emerges sometime later (a cursory search yielded no duration for the pupal stage).

Male flies have the tibia of the hind leg bowed in shape, and the hind femur swollen and armed with teeth. These features help embrace the female during courtship and mating. The general appearance of both genders is a more-or-less “stretch limo” of the fly world, sleek and slender, with a concave face and jutting antennae.

Mated females deposit small numbers of eggs in masses on emergent vegetation, so look for these insects in swampy areas, along the edges of ponds, and the banks of streams and rivers, even drainage ditches. A water course need not be flowing permanently to host both the flies and their snail prey. The adult flies overwinter, too, which explains how Heidi managed to find one so early this year.

Sources: Fisher, T.W. and R.E. Orth. 1983. “The Marsh Flies of California (Diptera: Sciomyzidae),” Bull. California Insect Survey vol. 24, 1-117.
Knutson, Lloyd Vernon and Jean-Claude Vala. 2011. Biology of Snail-killing Sciomyzidae Flies. Cambridge: Cambridge University Press. 526 pp.
Knutson, L. and R.E. Orth. 2001. “Sepedon mcphersoni, N. Sp., Key to North American Sepedon, Groups in Sepedon s.s., and Intra- and Intergeneric Comparison (Diptera: Sciomyzidae),” Proc. Entomol. Soc. Wash. 103(3): 620-635.
Maharaj, R., C.C. Appleton, and R.M. Miller. 1992. “Snail predation by larvae of Sepedon scapularis Adams (Diptera: Sciomyzidae), a potential biocontrol agent of snail intermediate hosts of schistosomiasis in South Africa,” Med. Vet. Entomol. 6(3): 183-187.
Neff, S.E. and C.O. Berg. 1966. “Biology and Immature Stages of Malacophagous Diptera of the Genus Sepedon (Sciomyzidae),” Blacksburg, VA: Virginia Polytechnic Institute, Agricultural Experiment Station Bulletin 566. 113 pp.
images of larva from Valley City State University, Valley City, North Dakota, Macro-invertebrate Lab, Digital Key to Aquatic Insects of North Dakota.