| Cheiracanthium inclusum | |
|---|---|
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Arachnida |
| Order: | Araneae |
| Family: | Miturgidae |
| Genus: | Cheiracanthium |
| Species: | C. inclusum |
| Binomial name | |
| Cheiracanthium inclusum (Hentz, 1847) |
|
| Synonyms | |
|
Clubiona inclusa |
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Cheiracanthium inclusum, alternately known as the black-footed yellow sac spider or the American yellow sac spider (in order to distinguish it from its European cousin C. punctorium), was formerly classified as a true sac spider (of the family Clubionidae), but now belongs to the long-legged sac spiders (family Miturgidae).[1] It is a rather small pale yellow species that is indigenous to the Americas and can be found living in the foliage of forests and gardens but also can inhabit human homes.[2] C. inclusum is also one of a handful of spiders found in North America whose bites are generally considered to be medically significant. C. inclusum is closely related to Cheiracanthium mildei, an introduced species native to Europe which is similar in appearance and natural history and can also be found in North American homes.[3]
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Like all spiders, C. inclusum has two body segments: a cephalothorax (fused head and thorax) and an abdomen. In females, the body measures between 5 and 9mm and in males, 4 to 8mm. The leg span however can be up to 1 inch with the front pair of legs being longer than the other 3 pairs.[4] Males tend to have a skinnier body and a larger leg span than females.[2] C. inclusum gets its 2 common names (yellow sac and black-footed spider) from its appearance. It is a pale yellow-beige colour with dark brown markings on its palps, chelicerae (jaws) and on the ends of its tarsi (feet). There is also often an orange-brown stripe running down the top-centre of its abdomen.[3] In terms of sensory structures, C. inclusum has 8 similarly sized eyes distributed in 2 parallel horizontal rows. However their eyes are thought to be less important structures due to the absence of light during the spider's nocturnal activity. The spider relies more on palps, sensory structures just behind the chelicerae on the cephalothorax, to sense its environment.[5]
C. inclusum are native to the New World (North, Central, and South America; and West Indies).[6] This species has also been introduced to Africa and Réunion.[7] They are most often found in trees and shrubs, but may also find shelter in houses and other human-made structures.[2]
Females of C. inclusum mate only once, and produce their first egg mass about 14 days after mating. Two sets of eggs are usually produced, but this can range anywhere from 1 to 5. Egg masses generally contain 17 to 85 eggs, although as many as 112 eggs have been reported in a single egg mass.[2] Egg lying generally occurs during the months of June and July; during this period, females lay their eggs in small (2 cm) silk tubes and enclose themselves with the eggs, protecting them from predators. Females stay with the eggs and juvenile spiders for about 17 days - until their first complete molt. Females that produce multiple egg masses build a second egg sac about two weeks after the juvenile spiders disperse. Males tend to mature faster (119 days on average) than females (134 days on average), but time to maturity can range from 65 to 273 days depending on a number of factors, such as temperature, humidity and photoperiod. They over-winter mostly as adults or sub-adults.[6]
Being nocturnal, C. inclusum feed and mate at night. C. inclusum do not make webs to catch prey; instead, they are active predators, feeding on a variety of arthropods such as insects and other spiders. Prey detection may involve detection of mechanical vibrations of the substrate, and vision seems to play an insignificant role.[8] During the day, they retreat in small silk nests similar to those used for reproduction. A new nest, which may be completely closed, open on one side, or open on both sides, is built every day in under 10 minutes.
C. inclusum are known to disperse easily between trees and shrubs. They do this by excreting a long silk thread that gets carried by the wind and sticks to a nearby structure, forming a scaffold between two structures. Alternatively, the spider may stay attached to the thread and balloon through the air.[6]
The bite of these spiders is believed to be venomous to humans but rarely produces more than local symptoms. They are believed to produce a high percentage of the spider bites suffered by people, possibly because they wander about when people cannot see well or are asleep, and so they may get squeezed and bite to protect themselves. Bites that occur to farm laborers may occur because spiders hiding in their shelters on leaves may get squeezed.
It has been noted that a large number of bites attributed to the brown recluse spider may actually be the result of yellow sac spider bites, which possess a cytotoxic venom known to contain several proteolytic enzymes including alkaline phosphatase, deoxyribonuclease, esterase, hyaluronidase, lipase, and ribonuclease.[9] These enzymes can cause localized tissue necrosis (which may be similar to that caused by a recluse bite), though the symptoms are less severe and do not result in the systemic effects occasionally seen with recluse envenomations.
However, the view that this spider is dangerous to humans has been questioned. A recent study of 20 confirmed yellow sac spider bites revealed no evidence of necrosis; further review of international literature on confirmed bites revealed only a single bite with mild necrotic symptoms.[10]
Although the danger of C. inclusum may be questionable, the spider bite may cause local redness with stinging pain.[11] When it's found immediately wash from the bite site to prevent further venom entering the wound in case of the spider bite. Thoroughly wash the wound with soap and water. Do not use alcohol. Also do not engage in any activity that raises the heart rate. An ice pack may be applied to draw out the venom. Do not squeeze or pick the bite site. It may cause secondary infection or spread the poison to a wider tissue region. If the pain persist for a long period, show it to a doctor for a proper measure.[12]
C. inclusum bites usually occur when the spider is threatened.[2] People might threat C. inclusum without noticing in some incidents. For example, while C. inclusum is hunting during the night time, people may roll over and press the spider accidentally or put on a coat that stayed in the closet over the winter without noticing the spider inside.[13] Also, putting the shoes on while C. inclusum is in there. As the weather cools down, it is more likely for the spider to invade the indoor structures. To prevent the bite from C. inclusum, secure all screens on the windows and doors. Do not stack fire wood near the house. Also, take care of all the house pests such as ants and silverfish that attract spiders.[14]
In March 2011, Mazda initiated a recall of 65,000 Mazda6 automobiles after webs of this species were found to have clogged fuel system ventilation tubes.[15] It is unclear why the spiders were drawn to build webs inside this particular vehicle, but the problem appeared to be widespread, though rare, across the United States.[16]
