INTRODUCTION
The common name comes from the retreat they build which is a flattened silk tube or
sac where they spend most daylight hours; they do not build webs. These spiders are more
than nuisance pests because 3 species are probably responsible for a great many cases of
indoor spider bites throughout the United States. Various species are found throughout the
United States.
RECOGNITION
Adult female body length 3/16-3/8" (4.9-10 mm), adult male body length about
1/8-5/16" (4-8.5 mm). Color pate yellow to pate green, with chelicerae and palp tips
brown, and legs and abdominal midline slightly darker, or with cephalothorax orange brown
to reddish top and bottom, abdomen pale yellow to light gray with anterior median area
slightly darker, and anterior legs darkest with other legs becoming increasingly paler
towards rear pair. With 8 subequal eyes in 2 rows, front row slightly curved forwards and
posterior row's median eyes slightly nearer to each other than to lateral eyes and/or
slightly curved towards front. Anterior spinnerets conical with bases touching or almost
so. Anterior legs (I st pair) longer than 4th pair, or 1 st pair shortest of all pairs;
tarsi with 2 claws each.
SIMILAR GROUPS
Ground spiders (Gnaphosidas) with front row of 4 eyes slightly curved to rear and
middle 2 eyes slightly larger and dark (vs. other 6 eyes pale) and anterior spinnerets
cylindrical in shape and distinctly longer than others.
REPRESENTATIVE SPECIES
- Trachelas tranquillus (Hentz). Adult female body length 5/16-3/8" (7.5-10 mm), male
about 3/16" (5.5 mm); color orangish to reddish and yellow, cephalothorax
(carapace/top and sternum/bottom) orange brown to reddish, abdomen pale yellow to light
gray with anterior median area slightly darker, and anterior legs darkest with other legs
becoming increasingly paler towards rear; Ist pair of legs shortest of all pairs of legs;
found in New England and adjacent Canada southwest to northern Alabama and Georgia, and
west to Minnesota and Kansas.
- Yellow sac spider, Chiracanthium inclusum (Hentz).
Adult female body length 3/16- 3/8" (4.9-9.7 mm), male 1/8 - 5/16" (4-7.7 mm);
color light yellow with chelicerae and palp tips brown, and legs and abdominal midline
slightly darker; lst pair of legs shorter than 4th pair; found throughout the United
States except for most northern tier of states.
- Yellow sac spider, Chiracanthium mildei L. Koch. Adult female body length 1/4-3/8"
(7-10 mm), male 3/16 - 5/16" (5.8-8.5 mm); color light green to yellow-white with
chalicerae and palp tips brown, and legs and abdominal midline slightly darker; lst pair
of legs shorter than 4th pair; introduced from Europe, found in New England, New York, New
Jersey, Alabama, Missouri, and Utah.
BIOLOGY
In the New England states, the yellow sac spider females lay their eggs in June
and July in a loose mass covered only with a thin white silk sac. The egg sac is kept in
her retreat indoors but it is often located in a rolled leaf outside. The female usually
stays nearby on guard. Outside, the spiderlings overwinter and become adults the following
May and June. They live about one year.
In the New England states, T. tranquillus females lay their eggs in the autumn in a
white lens-shaped egg sac, about 3/8" (IO mm) in diameter and 1/8" (2.4 mm)
high. The egg sac contains 30-48 eggs. Since the egg sacs can be found until November
(October in Kansas), they probably overwinter with spiderlings emerging the following
spring. In the New England states, adult males are found from late July through August and
aduli females may overwinter.
The 3 species of sac spiders detailed above are of medical concern because of the many
spider bites attributed to them. It is estimated that the 2 yellow sac spiders (C.
inclusum and C. mildei) may be responsible for many bites on people indoors. However, few
bits cases are reported, apparently because the spider is rarely caught in the act,
captured, and/or properly identified. Their venom is a cytotoxin and primarily affects the
tissues at the bite site. The bite may not be felt by some, but most people report a sharp
pain at the time of the bite. The bite seldom results in more than localized redness, a
burning sensation, and slight swelling at the bite site which may last for 24-48 hours.
In more severe bites or reactions, the localized burning sensation lasts about 30-60
minutes and residual pain for up to 3 days. During the following 1-8 hours, the reddenec
area may enlarge and fill with puss. Occasionally, a systemic reaction may occur which is
characterized by fever, malaise, stomach cramps, and nausea. Ulceration may occu over a
week and result in a well-defined eschar (hard crust or scab) or pit developing This
ulceration normally heals itself in several weeks.
First aid consists of using hydrogen peroxide or alcohol to cleanse the bite area anc
prevent secondary infection, applying an ice pac to reduce swelling, keeping calm, anc
seeing a physician if systemic symptoms occur. Remember to attempt to collect the
responsible spider and take it with you for identification purposes.
HABITS
Although sac spiders can be found indoors throughout the year, they mor( commonly
enter structures in greater numbers in the early autumn when their foo( supply decreases
and temperatures cool. They enter through loose fitting and/ol unsealed doors, faulty
screens, windows, vents and utility lines, structural junctures, an( plant materials
brought inside. They may stay in crawl spaces and structural voids feeding on the resident
arthropod population, or they may enter the living space through gaps around ducts, light
and electrical outlets, plumbing, and molding.
Once indoors, they may build their silk retreats in the upper corners and the ceiling
wall junctions of rooms and rest there during the day; in basements and crawl spaces
retreats are found where joists and band boards meet the subflooring. At night, sa(
spiders are often seen running on the ceilings and walls, but if disturbed they readily
drof to the floor and seek cover.
Bites usually occur when the spider crawls into clothing or bedding and become,,
trapped against a person's skin. However, C. mildei was once observed to crawl on E
person's arm and then to bite repeatedly without provocation.
Outside, sac spiders build their silk retreats under items
lying or piled on the ground such as stones, landscape timbers, firewood piles, lumber,
logs, and other debris. They can also be found in garages and outbuildings such as sheds
and dog houses. On the outside of buildings, they can be found at structural junctures,
upper corners of windows, behind shutters, and under eaves and overhanging shingles. Other
places include on long grass and weeds and in the leaf litter.
