Monday, December 24, 2012

Button/Widow Spiders - Family Theridiidae


-          - Black Button/Widow Spider: (Family Theridiidae - Latrodectus indistinctus/renivulvatus/cinctus/karooensis) Almost every major region of Africa has at least one of these species present, with the greatest density occurring in Southern Africa.  Black Button Spiders can inject strong neurotoxic venom, potentially causing heart palpitations, severe anxiety, chest pains and difficulty breathing.  However, these spiders are shy, retreating, and not aggressive. They are bound to their webs and will most often go out of their way to AVOID humans.  They also have a habit of wrapping their prey in silk before injecting venom, further reducing the chances of receiving a bite.  Victims should be kept calm and reassured that they will be fine.  However, medical attention should be sought as soon as possible, and antivenin should only be administered after observing real symptoms by a qualified medical professional.
African Black Button Spiders are generally almost completely black with some variation of a red marking on the dorsal (top) side of the abdomen.  This differs from some North American Species which are known for their red hour-glass markings on the ventral (under) side of the abdomen.  Black Buttons create messy looking space-webs, and often have several smooth round white egg casings in a retreat to one side of the web.
Similar specie: False Button Spiders (also Theridiidae, genus Steatoda) can easily be confused for a Black Button, except for the lack of any red markings on the abdomen.  Some have whitish/creamy markings on the abdomen.  Although, the venom from Steatoda is not nearly as toxic as that from Latrodectus, it can still produce a fair amount of pain and dizziness.
Steatoda sp. - FALSE BUTTON SPIDER (female): Notice the lack of any red markings on the top of the abdomen.  
Steatoda sp. - FALSE BUTTON SPIDER (female): Notice the lack of any red markings on the top of the abdomen.  
Brown Button Spider: (Family Theridiidae - Latrodectus geometricus): L. geometricus is one of the most widely spread spiders in the world, and occurs across every continent (other than Antarctica). The venom from Brown Button Spiders (also neurotoxic) is generally considered to be only 1/4th as virulent as that of the Black Buttons.  Symptoms of a Brown Button bite would be similar to those of a Black Button, but to a much lesser extent.
Brown Buttons vary from black to light brown with various markings on the top of the abdomen and a distinct red hourglass marking on the ventral side of the abdomen.  Their webs are similar to those of Black Buttons, but their round egg sacs are covered in spikes, rather than being smooth.
Latrodectus geometricus - Brown Button Spider: Very distinct red "hourglass" marking showing under the abdomen.  The often hang upside down in their webs, making this marking very visible.
Latrodectus geometricus - Brown Button Spider:  Hourglass marking just visible here.  Notice the variation in colouration on the top of the abdomen.  They can range from jet black, to brown, to striped or spotted, but the hourglass is always present.
Latrodectus geometricus - Brown Button Spider:  With Solifuge prey.
Not all member of this family are dangerous.  Dew Drop Spiders (Argyrodes spp), mentioned in the post about Kleptoparisitism are also members of this family.
House Button Spiders are also members ore Theridiidae, but are similarly harmless to humans

Sunday, December 23, 2012

What Is A Spider?


What is a spider?
The Order Araneae (Spiders) is the largest order within Arachnida, and spiders are found in every part of the world, except Antarctica.  Although many people think of spiders as being insects or “bugs”, they are in fact different in many ways from Insects.
Spiders
Insects
2 body parts (cephalothorax & abdomen)
3 body parts (head, thorax, abdomen)
4 pairs of legs
3 pairs of legs
2-8 simple eyes
Compound eyes
Do not have wings
Most have wings or vestigial wings
Carnivorous
Herbivorous and carnivorous
Ecdyse from spiderlings to adults
Complete and incomplete metamorphosis

Spiders have 8 jointed legs, 2 distinct body parts, 2-8 simple eyes, exoskeletons, silk glands (and spinnerets) and all but one family have venom glands.  There are approximately 79 families of spiders in Africa, representing about 72% of all the spider families in the world, and they can be split up into two groups: Araneomorphae and Mygalomorphae.
Araneomorphae:
Araneomorphs are what most people think of when they imagine a true spider.  Many Araneomorphs are conspicuous, easy to find, and build webs.  The quintessential orb-webs and cob-webs we all know are made by Araneomorphs.  However, not all Araneomorphs build webs; there are also several types of burrowing and free-living Araneomorphs.
Mygalomorphae:
Most African Mygalomorphs are large, robust ground/burrow dwelling spiders, most of which, despite their ‘scary’ appearance, are harmless to humans.  They have small venom glands and are often not aggressive.  Baboon and Trapdoor spiders and their relatives are Mygalomorphs
Araneomorphae
Mygalomorphae
More highly evolved
More primitive
1 pair of booklungs
2 pairs of booklungs
Chelicerae strike horizontally (against each other)
Chelicerae strike vertically (with each other)
Web-bound, burrowing, or free living
Most are burrowing or ground dwelling.
Araneomorph - In Web: Tetragnathidae -
Silver MarshSpider

Mygalomorph - Burrowing: Theraphosidae -
 Baboon Spider











Definition – Booklungs: Several thin plates of permeable membrane where gas exchange takes place with oxygen on one side of the plate and blood on the other.
Spider ecology:
Despite the negative image many people have of spiders, they play an important role in a functioning, healthy ecosystem.  With almost 8,000 different species from 79 different families represented in Africa, spiders inhabit every type of ecosystem and biome on the continent, and are an important food source for a diverse number of larger (and smaller) predators.  As spiders are carnivorous themselves, they are also important biological controllers of their prey species, keeping insect numbers in check. 
 - If every spider on the continent were to suddenly disappear, we would drown in a sea of insects!
Spiders are a fascinating group of organisms to study; behavioural differences and colour variations are as numerous as the species themselves.