Monday 1 June 2015

Orb Web Spiders of Zululand - by Frikkie Loots (Advanced Course Year 2 Student)

Nephilidae (Golden Orb-Web Spiders)
by Frikkie Loots

General Information about Nephilidae
The spider family Nephilidae is large, with 75 described species in four genera. They were firstly grouped in the families Araneidae and Tetragnathidae. The genus Singafrotypa was moved to Araneidae in 2002

The generic name Nephila is derived from Greek, "nen" meaning "to spin" and "philos" meaning "love" thus meaning "fond of spinning".  In South Africa, we have 3 genera represented by 6 different species.

Mating and reproduction
Nephilidae have great sexual dimporphism. The pedipalps have  evolved into enlarged, complex palps which break off inside of the females' copulatory openings after copulation.

The broken palps serve as mating plugs, which makes future matings with a mated female more difficult. This genera of spiders also participate in mate-guarding; a mated male will stand guard by his female and chase off other males, thereby increasing the mated male's paternity share. Mated males are castrated in the process of mate plugging, though this may be an advantage in mate guarding, as mated males have been observed to fight more aggressively and win more frequently than virgin males. 

So while the female spiders are still polyandrous, the males have become monogamous.The female Nephila constructs her egg sac on a leaf or tree bark; and produce about 400 - 1500 eggs per sac.

Prey capture
A large vertical, sulfurous yellow orb-web is constructed, which has the top section missing in adult webs.

Juvenile spiders construct complete orb webs. In semi-social populations, their webs are joined together forming an awesome, almost impenetrable curtain of webs. These webs are supported by anchor strings of silk in front and behind the orb-web.

The web is usually supported between two trees, buildings, fences and can span enormous spaces, with the orb up to a meter wide, about 1.5 meters or more from the ground and is capable of capturing small birds. There is no evidence that these birds are eaten but they may be cut out of the web by the spider.
Unlike most orb-webs, nephilid webs are partially repaired and not replaced. Most of the activity is conducted by day (diurnal).

The obvious colour of the main strands are believed to act as a "house hold insurance policy“ to the spider by advertising it's presence to large creatures such as birds, so that they don't damage it by flying through.

Building such elaborate webs is energy expensive and preventing large scale damage to the web is important.Some theories suggest that the UV properties of the silk attract insects in the same way that the UV pathways leading to the nectar in flowers do.

Commensal species
There are often one or more tiny spiders with silver triangular abdomens on Nephila webs. These are called dewdrop spiders of the genus Argyrodes (family Theridiidae) and they clean the orb-webs of prey too small for the host spider.

The South African Orb-web species:

 Nephila komazi  (Giant Nephila)
The largest of the Nephiladae was believed to be extinct until in 2009 it was re discovered in the Zululand area and now can also be found in Madagascar. 

Largest of the Golden Orb web spiders with a leg span measuring at 120mm (12cm). Its carapace is silvery, Abdomen is long and cylindrical extending beyond its spinnerets. It has a bold black and pale yellow pattern on its carapace which is one of the key ways to identify this spider. 

Legs are black with little brushes of hair on them. This spider is so large in fact that it’s been known to catch birds! Their large Orb webs are built between trees with the female sitting in the middle and the not so much smaller males (which is rare in the Nephila family as usually the males are substantially smaller than the females) sitting on the edges of the web.

Nephila fenestrata  (Black-legged Nephila)
One of the more common spiders of the Nephila family that we can see here in KZN as they love forested areas, usually between January to July (but if conditions are right they will stay till the end of August). 

Easiest way to identify this spider is by its black, very hairy legs. Carapace is oval in shape and has white and black patterns with often a few yellow spots. The Black-legged Nephila’s like to make their nests either in the open or amongst trees, but they also seem to enjoy making their webs near human habitations which often causes problems as many people don’t enjoy waking up to a spider that has a leg span of about 100mm (10cm). 

The females generally sits in the middle of the web and the much smaller males sit around the edges of the web.

Nephilengys cruentata (Hermit Spider)
The hermit spider is quite a beautiful spider. For a spider it can grow to be rather large. These particular spiders like to build a funnel shaped web where they can hide from view and be safe during resting times and times of stress. 

Attached to that funnel shape is a normal spider web that is used for catching prey. These are quite secretive spiders and do not like to be out in the open and that is why the spend most of their time in the safety of their funnel. 

They have a beautiful coloration which in nature almost always means danger. Their legs are red, yellow and black and their abdomen is black with white spots. As with all spiders the female is bigger than the males.

This spider in particular normally can be found with many of the same species in close proximity. They are also commonly found near and around human dwellings.

Clitaetra irenae- Tree Nephila
This Spider is quite hard to find as its colouration is perfect for blending in with its surroundings (normally tree bark), and you do need to know what it looks like and where to look. 

It is called the Tree nephila as it lives on the tree bark where it constructs a permanent web. Its colouration is mostly a pale brown with some spots of red and black.

This spider occurs in the coastal plain forests of Maputaland in KwaZulu-Natal South Africa. It loves very close or dense canopy.

Nephila senegalensis (Banded-legged Nephila)
A beautiful spider that has a very interesting and distinguishing pattern on its legs. It has two yellow streaks on its front legs which gained it its name banded-legged nephila. Being a Nephila it is a large spider and can be viewed near Oom Pine’s house in the forest.

Nephila inaurata (Red-legged Nephila)
The legs on this species are red and almost see through. They are large spiders and like to make webs near and around human settlements and buildings. They have a small abdomen for their size and quite long legs.