Latrodectus (button spiders, widow spiders)

Latrodectus (button spiders, widow spiders)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Arthropoda > Arachnomorpha > Cheliceriformes > Chelicerata > Euchelicerata > Arachnida > Araneae > Araneomorpha > Family: Theridiidae

This is a notorious genus in that certain species are highly toxic and, under rare circumstances, can kill people if they are bitten. The name widow spider arises from the fact that females often consume the male after mating. There are 6 species in South Africa, 5 of which occur in the Western Cape. The very common species, Latrodectus geometricus, or Brown or Geometric button spider occurs around every home, outside under window ledges, behind drain pipes, under wood piles etc. Although its bite can sometimes be troublesome, it is not life threatening as is the case with of most of this group. However, Latrodectus indistinctus, or the Black Button spider presents a serious problem. Its venom is neurotoxic (affects the central nervous system). This spider does not occur around the Cape Peninsula but distribution starts from about Bellville and extends north and east. Bites used to be very common during the manual harvesting of corn but these days with mechanised harvesting, bites are quite rare.

The Black Button spider, Latrodectus indistinctus, is always dark brown to black with a silky appearance. Dorsally the abdomen can be scattered with white or red flecks or bands or can be unmarked. The Brown Button spider, Latrodectus geometricus, is very variable in colour ranging from cream, beige, brown, olive green to black but always with dorsal geometric markings that radiate down the sides of the abdomen. Sometimes the markings on Latrodectus geometricus are not that apparent on those that are darkly coloured or black and the latter could be confused with Latrodectus indistinctus. However, the 2 species can always be differentiated by the orange hour-glass marking on the underside of Latrodectus geometricus while Latrodectus indistinctus has the red stripe/s on the dorsal side at the end of the abdomen above the spinnerets. This stripe/s radiates up the abdomen but as the spider grows, this stripe/s reduces with each moult ultimately leaving an indistinct mark, hence the name Latrodectus indistinctus. A further difference is the egg sac. Latrodectus geometricus has a spiked egg sac while that of Latrodectus indistinctus is smooth.

Button spiders are very timid, usually retreating when disturbed or dropping to the ground and playing dead. Bites result from handling or when they are trapped and squeezed.

The main 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.

Symptoms are less severe with the Brown button spider.

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. All Latrodectus bites should be treated and monitored.

Species native to southern Africa

Latrodectus cinctus Blackwall, 1865 Recorded from Africa, Cape Verde and Kuwait.
Latrodectus geometricus (Brown widow, Geometric button spider) C.L. Koch, 1841 Cosmopolitan.
Latrodectus indistinctus (Black button spider) O.P.-Cambridge, 1904 Namibia, South Africa.
Latrodectus karrooensis Smithers, 1944 South Africa
Latrodectus renivulvatus Dahl, 1902 Africa, Saudi Arabia, Yemen
Latrodectus rhodesiensis Mackay, 1972 Southern Africa.