Spider Bites

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All spiders (except the family Uloboridae) have venom glands but not all are venemous to man. In fact very few species pose a threat to man. Some spider bites might need medical attention even if the species is recognised as not being venomous to man as secondary infections can occur.

Spider venom, like snakebite venom, is generally either neurotoxic or cytotoxic. Generally, it is the web dwellers that have neurotoxic venom and the non-web dwellers have the cytotoxic venom.

Cytotoxic venom affects the cellular tissue usually restricted to the area of the bite but can spread. The bite is at first painless with symptoms developing about 2-8 hours after the bite. It starts by resembling a mosquito sting, becoming more painful and swollen. Eventually it ulcerates into a large surface lesion (up to 10 centimetres) that will require medical attention. This type of bite would result from members of the genera Loxosceles (family Sicariidae) and Cheiracanthium (family Miturgidae). Treatment with antibiotics might be required to treat secondary infections. The wound will take between two and 4 weeks to heal but the lesion might take months to improve. In some cases ugly scarring might occur that might require plastic surgery.

Sac spider, Cheiracanthium fulcatum. [image N. Larsen ©]


Sac spider bite.	Sac spider bite at 3 days. (image by A. Pollard)

Sac spider bite at 10 days. (image by A. Pollard)	Sac spider bite at 6 weeks.

More specifically, the bite of Cheiracanthium presents as two spots, 4-8mm apart, where the fangs penetrated the skin and are yellow-green, the colour of the venom. After 4-8 hours, mild inflammation, swelling and pain develop. A blister may form over the necrotic lesion after a few days. After this sloughs, an irregular round, ulcerated wound of about 10mm remains. The wound is inflamed, swollen and painful. The wound could start to heal after 10 days but occasionally takes months. In some extreme cases, skin grafts have been necessary. The use of antibiotics is usually required should secondary infections set in but this could be prevented by the use of an antibacterial cream such as Betadine. There is no antivenom and an anti-tetanus injection is usually necessary. Some patients develop a mild fever and headaches after about 3 days and the condition is sometimes misdiagnosed as tick bite fever. However, tick bite fever symptoms develop after about a 10 day incubation period after being bitten, by which stage the bite will have turned black and the surrounding area swollen and red.

The venom of violin spider (Loxosceles) is also cytotoxic with similar symptoms to the sac spider.

Violin spider, Loxosceles sp. [image N. Larsen ©]


Violin spider bite at 3 days.	Violin spider bite at 11 days.	Violin spider bite at 14 days.	Violin spider bite at 4 weeks

Tissue damage from a bite by Sicarius (family Sicariidae) is far more extensive and severe. Bites to humans are not well documented. However, experimental rabbits died within 4-6 hours and autopsies revealed extensive damage to subdermal tissue and skeletal muscle. There was swelling of the liver and damage to heart and kidney tissue as well as blocked pulmonary arteries.


Sicarius. [image N. Larsen ©]

Not everyone will be affected in the same way by a spider bite. The severity would depend on the amount of venom injected, the health of the patient or if the patient has allergies, the age of the patient (small children and the elderly would be more adversely affected) and the site of the bite. Some patients display symptoms of stress that can be misleading, leading one to fear the worst of a harmless spider bite.

Neurotoxic venom affects the neuromuscular junctions, and bite symptoms involving this type of venom are:

severe pain in the chest and abdomen
anxiety, raised blood pressure
breathing difficulties and heart palpitations
nausea and vomiting
sweating, excessive salivation and watery eyes
the body temperature could either fall or rise above normal and the blood pressure may rise with an increased pulse rate
a rash might develop

In this venom category it is only the back button spider, Latrodectus indistinctus, bite that would require urgent medical attention although Latrodectus geometricus envenomation will also require medical attention especially in the case of children, the elderly.


Latrodectus indistinctus (Black button spider). [image N. Larsen ©]

The main signs and symptoms of Latrodectism (Button spider envenomation):
sharp burning pain at the site
pain spreads to lymph nodes within 15 minutes
severe muscle pain and cramps within an hour, resulting in tightness in the chest and difficulty with walking
anxiety, sweating, fever, slurred speech, nausea and headaches.

Less than 5% of untreated cases result in death, usually as a result of respiratory failure. In fact, there have been no deaths from button spiders in the last 4 to 5 decades. Those more severely affected are children (smaller blood volume) and the elderly who might suffer respiratory or heart failure. Symptoms are less severe with the Brown button spider, Latrodectus geometricus . All Latrodectus bites should be treated and monitored.


Latrodectus geometricus (Brown button spider). [image N. Larsen ©]

When someone is bitten:

Keep the culprit if possible. An identification of the spider would be necessary to determine the appropriate treatment, if any.
Keep the patient or the affected part as motionless as possible. However, this might not be practical if one is out in the wild. It is then preferable to get to help as soon as possible even if the patient has to walk.
Eating, drinking and smoking should be avoided.
Call for medical assistance
Keep the patient on his/her back with feet raised above the rest of the body. Cover with a blanket and keep the head to one side in case of vomiting
Loosen tight clothing
Apply artificial respiration should breathing stop

Apply crushed ice to the affected area. The cold helps to retard the venom action and reduces pain. This must be done within minutes of being bitten. Do not cool for an extended period and remove periodically for the feeling to return otherwise tissue damage might result.

DO NOT

Use alcoholic drinks as this could mask certain symptoms or exacerbate them.
Use potassium permanganate on the wound.
Cut the wound.
Use a tourniquet as this could aggravate local effects of the venom.
Use snakebite venom on spider and scorpion bite patients.