ARE SPIDERS DANGEROUS?
By Astri Leroy/ Prof Gert Muller
INTRODUCING SPIDERS
Spiders are small land-based predators with 8 jointed legs, external skeletons, two main body parts, simple eyes, no wings or antennae. They lay eggs but do not metamorphose. All spiders produce silk and many build beautiful webs.
They are probably the most abundant land-based predators and although insects are the primary prey, some can catch small birds, mammals, reptiles, amphibians and even fish.
Southern Africa with its varied topography, vegetation types and habitats from deserts to forests, mountains to wide grassy plains, man-altered landscapes and wilderness areas - has a huge number and diversity of these little predators. They range in size from the comparatively gigantic baboon spiders or “African Tarantulas” to adult spiders with body length of less than a millimeter. The majority are modest-sized, inoffensive and keep to themselves. There’s at least one and probably more not very far from you now. Don’t run away spiders are not aggressive- they’re not out to get you. So the answer to “Are spiders dangerous?” is generally “No”.
VENOM
All spiders produce venom, except members of one small family, the Uloboridae. Spider venom is a mixture of saliva, venom and digestive fluids, used to subdue, kill and digest their prey - usually invertebrates. In general it has little effect on large mammals, including people. A bite may hurt at first, can itch for several days but if left to subside without being scratched will disappear with no lasting ill effects. Venom does not persist in the body and the effects of a bite will not recur later. Spiders will only bite if squashed against our skin - they don’t even bite in self-defence as some larger creatures do. They do not make a living from sucking our blood and are not vectors of any human diseases. They cannot lay eggs under our skin and won’t make nests in our hair. In fact they will avoid contact with big, dangerous creatures like us at all costs. This means that spider bites are uncommon and the effect venom of most spiders on humans is unknown because they simply don’t and often cannot bite us. There are however a very small number of species in only three of the 71 families of spiders that occur in South Africa that DO have venom of medical significance and these are the spiders shown Below (We have more than 2200 species of spiders in South Africa).
SPIDERS WITH MEDICALLY SIGNIFICANT VENOM
Our button or widow spiders have neurotoxic venom (venom that affects the central nervous system).
BLACK BUTTON OR WIDOW SPIDERS
Family Theridiidae, species Latrodectus cinctus, Latrodectus indistinctus, Latrodectus karrooensis & Latrodectus renivulvatus
Black button spiders are regarded as the most dangerously venomous spiders found in Southern Africa. Those found in southern Africa do not have the red hourglass marking under the abdomen but can have a variety of pretty red and gold markings on the upper side, fading in older individuals to a dull red dot above the spinnerets or disappearing altogether.
Egg sacs are smooth, usually spherical, sometimes tear-drop shaped and about the size of a large green pea. Mature female’s abdomens are also about pea sized. They make three dimensional webs of very tough silk with a retreat to one side in a variety of sheltered spots, usually outdoors.
Males are very small and harmless to humans. The potent venom affects the nervous system, causing severe systemic symptoms and local pain, this is called Latrodectism. In South Africa there have been no recorded human deaths for more than 7 decades. An antivenin is available in South Africa. Although they are reluctant to bite, preferring to “play dead” if disturbed, proven button spider bites must be taken seriously and medical attention sought.
BROWN BUTTON SPIDERS (Widow Spiders)
Latrodectus geometricus and Latrodectus rhodesiensis Family Theridiidae
Brown Button spiders, despite their name, can be creamy white to very dark blackish brown. They do have a red or orange double-isosceles-triangle marking under the abdomen. Egg sacs of the Rhodesian Button spider are spherical, large and fluffy. The much more common Brown Button Spider’s egg sacs are spherical and covered in little silken spikes. They make three dimensional webs of very tough silk with a retreat to one side in a variety of sheltered spots. Brown Button Spiders are common, widespread and often found in and around human habitation. Males are very small and harmless to humans.
Brown button spider venom is similar to that of black button spiders but less potent. They are reluctant to bite, preferring to “play dead” if disturbed. Medical attention should be sought if symptoms occur although there are only a few known cases of Latrodectism from the bite of a brown Button Spider that have needed treatment. The antivenofor all cases of Latrodectism is available in South Africa. No human deaths have been recorded.
TREATMENT OF BUTTON/WIDOW SPIDER BITES (Neurotoxic venom)
Hospitalization and monitoring of vital signs for at least 24 hours
There are no investigations of value in establishing the diagnosis.
If symptoms develop (they don’t always) they should at first be treated symptomatically and in severe cases Latrodectus spider antivenin obtainable from South African Vaccine Producers (Pty.) Ltd. Tel (011) 386-6000 or 386-6063 must be administered and this should only be done by a trained medical professional. It should be readily available and kept in all hospitals. Calcium gluconate solution can be given intravenously to give some relief from cramps. Patient should be hydrated intravenously.
The bite site must be kept clean, uncovered and not interfered with.
Avoid Opioids and given a Tetanus toxoid.
VIOLIN SPIDERS
Family Sicariidae, genus Loxosceles
6 species Loxosceles bergeri, L parramae, L pilosa, L simillima, L speluncarum, and L spinulosa
Violin spiders are smallish to medium-sized, unremarkable free–living nocturnal hunters and a variety of subdued brownish colours. The “violin marking” on the head region is not always visible and is not a reliable identification mark. They don’t construct webs to catch their prey but rest under logs and bits of fallen wood etc., by day in a retreat of a few strands of soft, bluish silk. The danger from violin spiders is hugely exaggerated. They will only bite if inadvertently squashed again the skin. The venom is cytotoxic (cell destroying) to humans and can, but seldom does, cause long-lasting necrotic wounds. Bites are not life threatening but medical attention should be sought for proven Violin Spider bites. Treatment is supportive and symptomatic. No antivenin is available or necessary.
Here’s what Dr Ansie Dippenaar-Schoeman, a world-renowned scientist who has worked with spiders all her life says about them:
”Of the medically important spiders, it is especially the VIOLIN spider that causes the greatest confusion. Over the last years e-mails have been circulating claiming that violin spiders have become a serious problem in South Africa and that their numbers are increasing at an alarming rate.
Violin spiders are regarded as rare spiders by the arachnologists in South Africa with very few specimens recorded from houses. Surveys in South Africa over the last forty years support this statement. In the South African National Collection of Arachnida, which houses more than 140 000 spider specimens collected over a 40-year period, only 120 specimens (0.08% of the collection are violin spiders. Of these 120 specimens, only 11 were collected inside buildings.
Their rarity is confirmed by surveys undertaken over the last six years as part of the South African National Survey of Arachnida (SANSA). Of the more than 10 000 spiders identified annually, violin spiders are rarely encountered.
As part of SANSA, a virtual museum www.arc.agric.za:8080 is available to the public and it contains photographs of spider submitted – most of which were found in and around house. Of the more than 3000 photographs received to date, only 10 are of Violin Spiders, and five of these were photographed at the same locality in the Free State.” More information is available on the ARC-PPRI website
http://www.arc.agric.za/arc-ppri/Pages/Biosystematics/Arachnida-Research.aspx.
SIX-EYED SAND SPIDERS, SIX-EYED CRAB or SIX-EYED DESERT SAND SPIDERS
Family Sicariidae, Sicarius hahni,
Sicarius spatulatus, Sicarius testaceus
Six-eyed sand spiders are found in arid areas of fine sand where they remain immobile just below the surface. They are restricted to dry sandy habitats and can be found in the soft soil at the mouths of caves and overhangs or in the shelter or rocks. Although their venom is potentially dangerous there have been no proven records of bites in South or southern Africa from these spiders.
Tests show that the venom of six-eyed sand spider has both cytotoxic and hemotoxic elements which mean it could cause both tissue damage at the site of the bite and internal hemorrhaging. No human envenomation has been recorded so we simply don’t know either what the effects would be or what treatment should be recommended, but probably the same as for violin spiders, i.e. supportive and symptomatic. No antivenin is available.
TREATMENT OF VIOLIN AND SIX-EYED SAND SPIDER BITES
(Cytotoxic venom)
Treatment is given to promote healing and limit secondary infection. The bite site must be kept clean, dry, uncovered and not interfered with. If infection does occur, antibiotics I.V. and a tetanus toxoid should be administered. No antivenin is available for cytotoxic spider bites. There are no investigations of value in establishing diagnosis.
SAC SPIDERS, YELLOW SAC SPIDERS, HOUSE SAC SPIDERS, LONG-LEGGED SAC SPIDERS
These are various common names given to the very common spider Cheiracanthium furculatum in the family Eutichuridae. Since the early 1980’s bites from the common House Sac spider Cheiracanthium furculatum have been believed to be medically important and to cause slow-healing (necrotic) sores. This reputation came about from a study conducted several decades ago using circumstantial evidence. We are not sure how the researchers proved that the sores were caused by a spider bite.
The media got hold of this research, it was repeated many times in both scientific and popular literature and a legend was born. Recent research suggests that their venom does not contain the compound that causes necrosis and that this reputation could be undeserved. (See reference section Vetter,R.S., Isbister, G.K., Bush, S.P., Boutin, L.J. Verified bites by yellow sac spider, etc.). House sac spiders are probably no more or less dangerous to humans than any other spider and like all spiders they try their best to avoid contact with us.
NOTES FOR MEDICAL PRACTITIONERS
Rick Vetter (2006) a medical entomologist from the USA says: “One of the very real problems with arthropod bites is that the bite causes itching, the victim scratches, introduces a secondary bacterial infection from grungy fingernails and such, a horrific wound shows up and then the wound is solely blamed on the arthropod when the real culprit is the bite victim him/herself.”
So when presented with a necrotic lesion think bacterial infection or one of the following
possible diagnoses to be investigated before blaming a spider:
ALTERNATIVE DIAGNOSES
A list of medical conditions that have been or could be misdiagnosed as cutaneous loxoscelism. Modified from Swanson & Vetter (2005)
Infections
Atypical mycobacteria
Bacterial Streptococcus - Staphylococcus (especially MRSA) - Lyme borreliosis - Cutaneous anthrax – Syphilis – Gonococcemia Ricketsial disease - Tularemia
Deep Fungal Sporotrichosis – Aspergillosis - Cryptococcosis
Ecthyma gangrenosum (Pseudomonas aeruginosa), Parasitic (Leishmaniasis), Viral (herpes simplex, herpes zoster (shingles)), Vascular occlusive or venous disease, Antiphospholipid-antibody syndrome, Livedoid vasculopathy,
Small-vessel occlusive arterial disease, Venous statis ulcer, Necrotising vasculitis, Leukocytoclastic vaculitis, Polyarteritis nodosa, Takayasu’s arteritis, Wegeners granulomatosis, Neoplastic disease, Leukemia cutis, Lymphoma (e.g., mycosis fungoides), Primary skin neoplasms (basal cell carcinoma, malignant melanoma), squamous cell carcinoma),
Lymphomatoid papulosis, Topical and Exogenous Causes, Burns (chemical, thermal), Toxic plant dermatitis, Factitious injury (i.e., self-induced), Pressure ulcers (i.e., bed sores), Other arthropod bites, Radiotherapy, Calcific uremic arteriolopathy, Cryoglobulinemia, Diabetic ulcer, Langerhans’-cell histiocytosis, Pemphigus vegetans, Pyoderma gangrenosum, Septic embolism
WESTERN CAPE VENOMOUS SPIDERS
Here are some of the types of venomous spiders you might encounter in the Western Cape Province:
Rain spiders
These spiders are often found curled up in the corner of a ceiling especially when it rains. They’re brown in colour with light and dark bands on the underside of their legs. They grow up to 10cm This docile spider feeds on insects and small vertebrates. The females build large messy leaf and silk nests in the plants in gardens. They are generally very docile and don’t bite easily, with the exception of the females on the nest, who will bite if the nest is disturbed. Their bites cause a mild pain similar to a bee sting and may be itchy for a while. It’s not needed to visit a doctor.
Baboon spiders
Baboon spiders are large, bulky and hairy spiders that can grow to up to 6 cm body length. Female baboon spiders live in silky burrows in the ground. Baboon spiders will lift their front legs when they feel threatened. The venomous bite results in a server pain lasting 10-40 hours. The use of pain medication is all that is required. It may be lethal to 20% of dogs bitten.
Black button spider
Black button spiders are common throughout the province and can be found in their three-dimensional webs in dark areas usually under stones, among grass or inside bushes but will rarely be seen. They’re black as adults with bright red patterns on the dorsal abdomen when subadult. The egg sac is round. Their venom is highly neurotoxic leading to respiratory failure, causing pain, sweating, nausea, disorientation and shortness of breath. You should seek immediate medical assistance at a hospital with a poison unit where it’s treatable with anti-venom in extreme cases.No deaths have been recorded from bites of this species.
Brown button spiders
Brown button spiders are commonly found in the Western Cape. They make three-dimensional webs in dark corners in a variety of microhabitats and are commonly found around houses. The egg sac is distinct with spikes. They’re brown with banded legs, and their abdomen varies from cream to black. They’re generally inoffensive and will escape into their retreat. If disturbed they’ll retreat, or they will fall to the ground legs tucked in but will bite when picked up. Spiders only bite when hurt.
Their venom is neurotoxic, and bites will be very painful. If bitten, symptoms can include nausea, sweating, disorientation and shortness of breath. You should seek immediate medical assistance at a hospital with a poison unit, especially in the case of children. The venom is less lethal than that of Black button spiders.
Sac spiders
Sac spiders are two-clawed, medium-sized spiders recognized by their uniformly straw-coloured bodies with the chelicerae and eye area blackish. Their eyes are in two rows, and the front legs are longest. They’re often found in plants, houses, in the folds of curtains, under clothes, behind picture frames and in the dark corners of cupboards. These spiders will build a silk sac where they’ll lay their eggs. Sac spider bites can be extremely painful,Despite disputes, this species does possess a cytotoxic venom and bites can result in tissue damage and should be treated as an open wound. If the wound goes septic or necrotic it is best to get to a hospital and go on a course of Prophylactic antibiotics. There are no deaths from this species.
Read more about other common spiders here
REFERENCES:
Croucamp, W., Preliminary analysis of the venom from the Sac spider Cheiracanthium furculatum (Araneae: Miturgidae). M.Sc. Thesis, University of the Witwatersrand, 1999.
Dippenaar-Schoeman, A.S., SANSA Newsletter No. 9 page 11. July 2009.
Dippenaar-Schoeman, A.S., ARC website www.arc.agric.za
Muller, G.J. Black & Brown button spider bites in South Africa. A series of 45 cases. S Afr. Med. J. 1993a; 83: 399-405
Muller G.J, Wuim C.A., Marks C.J., du Plessis C.E., Veale D.J.H. Spider bite in southern Africa, diagnosis and management. Continuing Medical Education, 2012. Vol. 30 No.10. (CME now incorporated into the S Afr. Med. J.)
Newlands G, Martindale CB, Berson SD, Rippey JJ, 1980. Cutaneous
necrosis caused by the bite of Chiracanthium (sic) spiders. S Afr Med J 57: 171–173
Newlands G, Atkinson P, 1988. Review of southern African spiders of medical importance, with notes on the signs and symptoms of envenomation. S Afr Med J 73: 235–239.
Newlands G, Atkinson P, 1990. Behavioural and epidemiological considerations pertaining to necrotic araneism in southern Africa. S Afr Med J 77: 92–95.
Snyman, C and Larsen, N, Spider bite and its treatment in southern Africa. Journal of Occupational Health Southern Africa. March/April 2005.
Vetter, R.S. Alleged Spider Bite. Western J. Medicine 173:357-358. 2000 - revised 2006
Vetter,R.S., Isbister, G.K., Bush, S.P., Boutin, L.J. Verified bites by yellow sac spider (Genus Cheiracanthium) in the United States and Australia. Am. J. Trop. Med. Hyg., 74(6), 2006, pp. 10
Comments