(Editor's Note: This article was originally published on August 10, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.)
Red spider lilies have been called 'silent ninjas'  for their habit of hiding any sign of leaf or stem for months and then bursting into extravagant bloom without warning in late summer or early fall. In Florida they are called 'hurricane' lilies because that is the season in which they appear. Red spider lilies, Lycoris radiata, produce leaves only after flowering. So for the period from spring through summer they are completely hidden--not a trace to be seen. Here spider lilies are most commonly naturalized in lawns, but their survival then depends on educating the person in charge of mowing to mow only before and after the red spiders have their day.
In about two weeks the magic is over. Then leaves will appear to defend the plant against obsessive mowers. In their native Asian homelands, (they are from Japan, Korea, and China, and east to Iran) Lycoris live in the forest litter beneath the shade of high trees. They excel in woodland settings. But some, like Lycoris radiata var. radiata do not mind full sun here in Alabama.
Other Lycoris - Surprise!
The genus Lycoris is one of sixty in the family Amaryllidacae and it is comprised of 20 species. While the genetic relationships among lycoris species have not yet been completely studied, it is clear that the genus is complex. There are many natural hybrids from old Asian gardens, so that the difference between species and hybrids is not entirely clear.
There are essentially only two types of Lycoris common to American gardens: the Southern suprise lily, Lycoris radiata, or 'red spider lily' (see thumbnail upper right) and Lycoris squamigera (See figures 1, 2, 3, 4, 5, 6). In general, the spider-flowered forms are not hardy and are restricted to Zones 7 through 10. The trumpet or funnel flowered forms tend to be hardy within Zones 5 through 9. Hardiness is actually correlated with the main growth period of the plant: most spider forms produce leaves in fall and winter after flowering. The hardy trumpet flowered forms tend to produce their leaves in spring. There are a few spider forms, such as L. caldwellii and L. chinensis that produce leaves in spring and are hardy. And there is at least one funnel flowered form, Lycoris x haywardii (See figure 7), that grows actively in the fall and winter and is tender like Lycoris radiata pumila, which is one of its parents.
Trumpet- or funnel-shaped flower forms of Lycoris.
Lycoris squamigera, the resurrection lily, is quite hardy and appears in gardens as far north as Zone 5. (See figure 1)
Lycoris squamigera has a lavender-pink trumpet shaped flower. Unlike, Lycoris radiata, it produces leaves in the spring (See figure 2) but then they disappear and the flowers appear as "naked ladies" in July or August, a few weeks before the red spider lilies.
There are a number of lycoris resembling L. squamigera that present interesting variations on the pink trumpet flower form. All of these, except Lycoris x haywardii, produce leaves in spring and are hardy through Zone 5.
Lycoris sanguinea is an apricot-orange form that is hardy and produces leaves in the Spring like L. squamigera. Images - (1) Lycoris sanguinea (Pacific Bulb Society image), (2) Lycoris sanguinea. (bulbmeister.com image), and (3) Lycoris sanguinea (Wikipedia image).
Lycoris incarnata, the peppermint stripe lily, has a white trumpet flower form resembling L. squamigera, with pink stripes.
Lycoris longituba has delicate pale white or yellow trumpet shaped flowers at the end of extended tubes: Here is a photo from the bulbmeister gallery and another from the International bulb Society gallery.
Lycoris sprengeri has blue tipped petals or there is a blue overlay on pink petals. It is called the 'electric blue' or 'tie-dye' lycoris. Here is a photo of the 'tie dye' lycoris from the pacificbulbsociety.org , and two more from the International Bulb Society. Here is still another photo of L. sprengeri from plantdelights.com.
Lycoris x haywardii (see Figure 7) is a cross between L. sprengeri and L. radiata var. pumila Because of its L. sprengeri ancestry, the petals are blue tipped. Because of its L. radiata pumila ancestry it is a winter grower like L. radiata var. radiata and not hardy . Regarding L. Haywardii, TomH3783 posted this quote from the Plant Delights catalog in Plant Files:
"This unique hybrid, named by Dr. Hamilton Traub in 1957, was discovered in a Chinese shipment to Wyndham Hayward of Florida in 1948. L. x haywardii combines the best traits of its parents (L. sprengeri x L. radiata var. pumila). The flower of L. x haywardii resembles that of L. sprengeri except for having more dissected petals (via L. radiata), and more of a magenta-pink flower color. Just as in L. sprengeri, the tip of each petal is bright blue, but the color does not permeate the center of the flower as it does in L. sprengeri. For us, this has been one of the earliest of the surprise lilies with a normal flowering time of July. " 
Lycoris caldwellii is a creamy yellow spider form lycoris with leaves formed in spring, like L. squamigera. tcfromky noted in Plant Files: "Lycoris caldwellii is a triploid Lycoris. It produces its foliage in spring, like L. squamigera, and is hardy to USDA zone 5. Flowers appear at about the same time as L. radiata." 
L. caldwellii is hardy through Zone 5 and blooms around the 1st of September in Indiana at Shields Gardens.
mgarr (figures 3, 4, and 5) has recorded the 'surprise' appearance and flowering of L. squamigera in just three days.
Spider Form Lycoris.
Although spectacular red spider lilies are the most familiar ones in the American South, lycoris spider lilies come in a range of colors.
White lycoris include Lycoris albiflora (Google Image Search), Lycoris albiflora (bulbsociety.org/gallery) and the creamy white Lycoris houdyshelii (Figure 9). These nearly white hybrids were photographed at the Riverbanks Botanical Garden, Columbia, South Carolina by Andy Cabe (bulbsociety.org/gallery): Chinese hybrid lycoris: a peachy 'Lycoris 'Blackcap Chitters Around the Willow' and white Lycoris 'Night Bells Ringing at Nanping Temple'.
Beyond the whites and off-whites there are a range of pastels including the spectacular Lycoris albifloria 'cherry pink' (Google Image Search) the peachy salmon Lycoris elsiae (bulbsociety.org/gallery) and the pale straw-colored Lycoris straminea (bulbmeister.com/gallery).
Lycoris radiata var. pumila (pacificbulbsociety.org) may be one of the ancestors of of the familiar Southern Lycoris radiata var. radiata (bulbsociety.org/gallery).
And finally the late yellows, Lycoris traubii and Lycoris aurea, extend the lycoris season into October. ( Figures 10, 11, and 12) The differences between L. traubii and L. aurea are discussed in this thread. 
How to Grow Lycoris. 
Bloom sequence. By selecting lycoris varieties the season of bloom can span the fall season beginning at the end of July and extending into October. Shields Gardens in Indiana place the bloom of L. longituba at about the same time as L. squamigera which usually starts the season. L. chinensis (Figure 12) blooms about the same time as L. radiata. L. Caldwellii blooms about September 1 in Indiana.
Elizabeth Lawrence, garden writer for the Charlotte Observer, (N.C.) from 1957 to 1971 reported the sequence of the "surprise lilies" for North Carolina. Beginning in August: L. squamigera, L. caldwellii Traub, L. albiflora, L. radiata, and finally the late yellows, L. traubii and L. aurea (not hardy in N.C.) appear in October.
Companion Plants. To avoid mowing away the spider lilies when they are "in hiding" they can be inter-planted with ground covers such as ferns, jasmine, English Ivy, liriope, or hosta. De Hertogh et. al  suggest these perennials to plant with lycoris: Coreopsis, Hemerocallis (yellow cvs.), Kniphofia (yellow cvs.), Leucanthemum (Shasta daisies), Peonies (white and yellow cvs.), Rudbeckia, Salvia, Verbascum (white cvs.), Buddleia, syriacus, Acer palmatum, Lagerstroemia.
Lycoris should be planted very shallow with the tops of the amaryillis shaped bulbs above or even with the surface of the soil. Ordinary garden soil with some added humus is fine. A handful of bone meal in the planting hole will get the plant off to a good start. You can pamper the plants by fertilizing with a low nitrogen fertilizer and watering regularly during the growing season, or not. The plants seem to thrive under good conditions with no care whatsoever. Withhold water and do not fertilize when the bulbs go domant.
The plants are dormant when they lose their leaves and go into "hiding" Lycoris squamigera (Zone 5 - 9) types of lycoris produce leaves in the spring. Lycoris radiata (zones 6 to 10) - red spider lilies - produce leaves in the fall after blooming. The types that grow in winter are more sensitive to frost and less hardy than the types that leaf out and grow in the spring.
Lycoris may bloom poorly when they become overcrowded. Lycoris divide readily and just a few bulbs will produce many offsets that can be divided and planted to produce new plants. Division of the offsets should take place as soon as the plants go dormant - when the leaves die back. June is often recommended as an appropriate time to divide lycoris. It is a good idea to mark the bulbs you plan to divide. Otherwise you may not be able to find them. The bulbs should be planted right away. The plants resent being disturbed and may not flower for a year or two as a newly divided plant.
Propagation. Some lycoris produce fertile seed and some do not. Hybrid plants may not produce fertile seed or the seedlings may not resemble their parent, so they are propagated from offsets. Some professionals suggest making bulb cuttings, but this is not normally practiced by gardeners.
Seeds are produced as the flowers fade. The fruit capsules contain a number of black seeds. Most advice about germinating lycoris seeds suggests that it is just too much trouble, especially when off sets are so readily produced by most plants. According to D.A. Cooke, "Lycoris seeds are often hard to germinate and the seedlings take 6-12 years to reach flowering size."  Sue Madison, however, says that blooming plants can be produced within 2 years time if the seedlings are kept growing and not allowed to go dormant. 
Cooke cites a study of eight sampled populations of L. radiata across South Korea representing a single clone. He says, "This has allowed the spread of sterile triploids and F1 hybrids at the expense of less attractive wild types while at the same time discouraging more elaborate breeding programs of repeated crossing and selection."
Mark Roh, horticulturalist for the US National Arboretum is addressing the problem of lost genetic material by maintaining collections of lycoris germplasm at the National Arboretum Asian Collection.
The mode of prolific distribution from offsets produced from sterile hybrid plants such as L. radiata var. radiata may account for the naturalization of sterile red spider lilies throughout the American South.
The Medical Potential of Lycoris.
All parts of the lycoris plant are considered to be poisonous, but those same alkaloids which render all parts of the plant deadly are now being isolated for their potential in treating some very serious diseases.
In China, Lycoris are referred to as "stone-garlic" - inedible garlic. The term for L. radiata in Cantonese refers to to Chung Kwai - who captures ghosts. One source, however, suggests that the bulbs could be eaten if the toxins were first leached out.
A Chinese company grows acres of lycoris flowers, sells potted plants, cut flowers, and distills and exports extracts from a range of lycoris species. Lycoramine extract is used to treat tumors, cancer, paralysis, and dementia. Galanthamine is used as a treatment for Alzheimers disease and paralysis.
A study of L. squamigera relates extracted alkaloids specifically to the treatment bird and animal influenza viruses. 
L. radiata var radiata has been included in the Plants of the Future for its medical value and for its easy cultivation in gardens. It is used as a treatment to counteract poison, swellings and ulcers, and can be applied as a plaster to burns and scalds. Its use in the treatment of cancer is being explored.
So now Lycoris, one of the world's most beautiful flowers, is no longer the 'flower with the dark secret' but one with the potential for easing pain and disease.
 Steve Bender. Splendid Spider Lilies. September 2007. Southern Living.com
 Synopsis of the Genus Lycoris. Bulbmeister.com.
 Lycoris radiata pumila. Image. pacificbulbsociety org.
 tcfromky from Mercer, PA (Zone 5a) contributed this information as Gardeners Notes to Plant Files on Oct 25, 2004.
 Lycoris caldwellii. www shieldsgardens com .
 Thread: Bulbs: Lycoris aurea or traubii. Discussants WillisTxGarden and dmj1218. www davesgarden com
 Guide to Growing Lycoris; Hardy Amaryllis. www plant-biology.com
 E. Lawrence and Bill Neal (editor). Through the Garden Gate. 1995. UNC Press. ISBN:0807845191
 A.A. De Hertogh, L.B. Gallitano, G. Hartley, M.E. Traer, and A.B. Russell. Department of Horticultural Science, NC State University. Holland Technical Service Bulletin Number 37. 2007. Photos. Companion plants for lycoris. www ces ncsu edu
 D.A. Cooke and PhenYenLeng. Notes on Lycoris Species. osemail.com.au
 Sue Madison. Germinating lycoris seeds. www bulbsociety.org/gallery
 Afredo Flores. Introducing Lycoris to US Flower Lovers. www redorbit com.
 L. radiata. Medical Value. "In China, the bulbs of L. radiata have been used as a poultice applied to burns.
The medical value of the plant is recognized to reduce swellings, and for its anti-cancer properties." ibiblio.org.
 Qian Qian Horticulture New Technological Development Company. www lycoris.cn
 Hyuk Joon Kwon, Sun Hee Cho, Sun Joong Kim, Young Jin Ahn, Jeong Chan Ra. Antiviral Composition Comprising Lycoris squamigera extracts. "Korean study (03. 10, 2008) of Lycoris squamigera extracts finds "excellent antiviral effects." Found that lycoris extract is effective in treatment for bird and other animal influenza diseases applied in food or 'pharmaceutical composition'. World Intellectual Property Organization.
Scott Ogden. (February 2007). Garden Bulbs for the South. Timber Press, Inc. 2nd Ed. ISBN 10: 0881928135.
ISBN 13: 978-0881928136.
Thumbnail. XENOMORPH. Lycoris Radiata var. radiata. Red Spider Lily. Plant files, January 25, 2005. "Late Summer, zone 9a."
 Lycoris squamigera. 'Resurrection Lily', 'Surprise Lily' WUVIE. PlantFiles, August 5, 2007. "As one pulls into our driveway, a row of Surprise Lilies greet you in late sumer, 2007."
 Lycoris squamigera, foliage. Tom H3787. PlantFiles, April 24, 2005. "Foliage - March 25th in Raleigh, N.C. foliage will dieback completely after May. Note rounded tips of leaves (unlike A. belladonna)".
, , & . Lycoris squamigera. Mgarr. PlantFiles, January 26, 2005. "It takes only three days for this bulb to come into bloom."
 Lycoris squamigera. TomH3787. PlantFiles, April 25, 2005. "Blooming August 1st. Raleight N.C., reflexed petals(unlike Amaryllis belladona)".
 Lycoris x haywardii. TomH3787. PlantFiles, July 20, 2008. "Picture taken July 19th at Plant Delights Nursery, Raleigh N.C."
Gardener's Notes: On July 8, 2006 TomH3783 from Raleigh, NC (Zone 7b) posted this quote from the Plant Delights catalog in PlantFiles:
This unique hybrid, named by Dr. Hamilton Traub in 1957, was discovered in a Chinese shipment to Wyndham Hayward of Florida in 1948. L. x haywardii combines the best traits of its parents (L. sprengeri x L. radiata var. pumila). The flower of L. x haywardii resembles that of L. sprengeri except for having more dissected petals (via L. radiata), and more of a magenta-pink flower color. Just as in L. sprengeri, the tip of each petal is bright blue, but the color does not permeate the center of the flower as it does in L. sprengeri. For us, this has been one of the earliest of the surprise lilies with a normal flowering time of July.
 Lycoris sprengeri. DiOhio. PlantFiles, October 27, 2004. "Lycoris sprengeri Tie dye Surprise Lily mid August blooms in Ohio."
 Lycoris x houdyshelii. TomH3787. PlantFiles, September 18, 2005. Gardener's Note: On Jul 8, 2006, TomH3787 from Raleigh, NC
(Zone 7b) wrote: Note from Plant Delights catalog: This rare, naturally occurring hybrid surprise lily (L. straminea x L. radiata var. pumila) is found in the Chinese provinces of Jiangsu and Zhejiang. It was first imported to the US in 1948 and named in 1957 by Dr. Traub in honor of bulb collector Cecil Houdyshel. The frilly light yellow flowers top the 20" tall stalks that seemingly appear from nowhere in mid-to-late August. Emerging from the center of the petals are long stamens, often tinged in light pink, like eyelashes on a lady of the evening. After flowering, the winter rosettes of 15" long basal leaves emerge in late September and persist all winter.
 Lycoris traubii. Golden Spider Lily. dmj1218. PlantFiles, October 14, 2007. "Photo courtesy of www.solasgardens.com."
 Lycoris aurea. 'Golden Spider Lily', 'Surprise Lily'. QueenB. PlantFiles, October 10, 2005.
 Lycoris chinensis, 'Golden Hurricane lily" dorothyabshire. PlantFiles, September 29, 2003."This plant blooms in September in my garden. It blooms a beautiful light yellow.
 Lycoris radiata var. radiata. 'spider lily'. creekowl72556. PlantFiles, May 2, 2008. "This picture was taken of my spider lilies about 3 years ago. They were in partial shade in N. central AR."