Yellow Sac Spider - Vector Control Services - Alameda County

Yellow Sac Spider
Males are 1/4” in
length, females
are 1/3-1/2” in
length
The Yellow Sac Spider (Cheiracanthium spp.) is considered the spider that most often bites people:
“Sac spiders may well be responsible for inflicting their bites on people more than any other spider.” 1
A recent critical review of documented Yellow Sac Spider bites revealed severe pain as the initial
symptom in 60% of the bites in the U.S. (C. milidei and C. inclusium) with lacking evidence for necrosis
caused by the bites 2 —a finding that suggest this genus of spiders should have a bite classification
of mild to moderate. There has been a long-running suspicion that necrotic wounds resulted from the
bite of these spiders, but anecdotal/circumstantial evidence does not convict a spider of inflicting a
bite. Many suspect spider bites in California are diagnosed as Loxoscelism (named after the brown
recluse spider that does not occur in California), but the offending arthropod is rarely caught in the act!
The Yellow Sac venom is classified as “cytotoxic” 3,4 —but the necrotic effect is usually very mild and
not well documented, except in some animal studies. 2 Interestingly, the yellow sac venom is quite unusual
as venoms go, now classified as a “two domain
modular toxin” in a recent study 3 , having cytotoxic
and neurotoxic properties.
These wandering, hunting spiders readily take up
residence in homes, and are somewhat reclusive in
nature. They often come out after dark to hunt for
food, while resting snugly in their “sac” during the
day. Their sac can often be detected in corners, and
next to door-jams. This sac can also contain a female
with her eggs (+-40) or spiderlings which she
will barricade herself in with until their first molt. The
young spiders are often difficult to detect due to their
light color, so often go unobserved until they mature.
Alameda County Vector Control, 1131 Harbor Bay Pkwy, STE 166, Alameda, CA 94502, (510) 567-6800
1.Stoy A. Hedges and Dr. Mark S. Lacey—PCT Field Guide for management of Urban Spiders. 2. Vetter et al Am. J. Trop. Med. Hyg., 74(6), 2006, pp. 1043–1048
3. NOVEL CLASS OF SPIDER TOXIN: ACTIVE PRINCIPLE FROM THE YELLOW SAC-Alexander A. Vassilevski et al JBC Papers in Press 2010 :4. Mallis, Nimth Edition

Yellow Sac Spider Chew Marks on Zip Sealable Plastic Bag
Observations 5
This is a sealable plastic bag (Ziploc) that a Yellow Sac spider was placed in one evening, but had
chewn it’s way out of by morning time. This was the second time this feat occurred by the able Yellow
Sac spider—escaping in the night. This is the only spider, over the years to chew it’s way out of a
plastic bag (authors observation). Other captive spiders, such as Black Widow, Wolf, Cellar, Orb
Weaver, Trap Door, Jumping Spiders and Wind Scorpions have pined for their freedom through the
night, but never put their mandibles to work to affect an escape!
Other interesting observations have been made regarding this spider, like curling up into a ball and
dropping to the ground when molested while crawling on a wall—they seem to be an expert in the
“quick-drop” and escape! Also, these spiders seem fairly flexible and are able to squeeze out of what
would normally seem to be a small opening (air hole) in a plastic container. And speaking of the quick
drop; this spider made me a believer in using a “motion detector” for the porch light, when one evening
I was entering my front door, something dropped on my neck, which I promptly whacked, and the Yellow
Sac spider was crushed by my blow! I did not feel a bite, but in the morning I had a small bump that
over the next few days developed into a pimple-like blister, that actually took months to completely
heal, and would occasionally break open and bleed. My dear doctor offered to excise the wound site,
but since it was but painful, only annoying, I let it heal on it’s own. Oh yes—the small crickets that I
feed to the other spiders, kill the Yellow Sac spiders… go figure!
5. Observations by Daniel Wilson ACVCDS