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Genus: Nephila (golden orb-web spiders) Life
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> Arachnida > Araneae
> Araneomorpha > Family: Nephilidae
There are 15 Nephila species known globally, four of
which occur in southern Africa. Nephila komaci,
which occurs in southern Africa, is the largest known web-spinning spider, and
members of Nephila make the largest orb webs - in fact large
enough and strong enough to accidentally catch small birds.
Description
The largest and most
impressive genus in the Nephilidae is Nephila. Females are large,
measuring 15 - 40 mm in length, with a leg span of 100 - 120 mm, while the male
is only about 5 - 9 mm, with leg span of up to 25 mm, and it is only about one
thousandth of the female's weight. Nephila komaci, found in Tembe
Elephant Park in South Africa and Madagascar, is the largest orb-web spider
known.
Distribution and habitat
These spiders occur in warm
regions of the world, mainly tropical and subtropical areas.
Species native to southern Africa
Four species are currently
described from southern Africa; pending a revision
further species may be described.
Prey capture
A large vertical, sulphurous
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
- like something from an Indiana Jones movie ( ).
These webs are supported by knock down strands of silk in front of and behind
the orb-web. The web is usually supported between two trees and can span
enormous spaces even across highways with the orb up to a meter wide, about 1.5
meters or more from the ground and is capable of capturing small birds (see
photo below). 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).
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Side-on view of Nephila fenestrata web
showing the knock-down strands of silk in front and behind the main web.
Also note how the top section of the web is missing, a characteristic of
webs made by adult Nephila. [photo Norman Larsen ©] |
Mating and reproduction
The Nephila male
copulates with the female while she is preoccupied with feeding. The males of
some Nephila species, once mated, will break off parts of their palps,
sealing the female’s genital openings. The female Nephila constructs her
egg sac on a leaf or tree bark; there are about 400 - 1500 eggs per sac.
There are usually one or two
amorous males in the female's web as well as
Juveniles are very variable
and can be confused with other species as the legs can be indistinctly banded.
The generic name Nephila is derived from Greek, "nen" meaning "to spin"
and "philos" meaning "love" thus meaning "fond of spinning".
Ecological interactions
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.
Predators
Nephila spiders are eaten by:
-
Cercopithecus pygerythrus (Vervet monkey).
Quote from South African National Survey of Arachnida (SANSA) Newsletter 11
& 12 (2010) (editors A. Dippenaar-Schoeman and C. Haddad). "Elsa van
Niekerk, the graphic artist at ARC-PPRI, is involved in the rehabilitation
of wild animals and she has observed some very interesting behaviour of her
vervet monkeys. They love feeding on large golden orb-web spiders. The
spiders are grabbed out of the web (sometimes two monkeys join forces to
pull it off successfully) and the spider is immediately put in their mouths
with the legs sticking out. The older individuals train the younger ones how
to do it. She has now also seen how they steal insects out of the orb-webs.
If this is a general behaviour they might have an effect on golden orb-web
spider numbers in areas."
Parasitoids
- Hymenoptera > Encyrtidae
- Amira durantae wasps parasitize Nephila eggs sacs,
with a specific record for Nephila inaurata (Prinsloo 1983).
Birds caught in webs
The webs of Nephila species are so large and strong
that they occasionally trap flying birds. There is no evidence that the spiders
eat the birds. In southern Africa, there are the following records of birds
trapped by Nephila spiders (information mainly from Brooks, 2012):
Brooks (2012) mentions a number of other birds from
southern Africa that have been caught in spider webs but the genus of spider is
not specified.
Links
Publications (by date)
- Webber JI. 1974. Blue waxbill caught in a spider's web. Ostrich 45: 262.
- Vernon C. 1976. Red-faced crombec caught in a spider's web. Honeyguide
85: 41.
- Prinsloo GL. 1983. A parasitoid-host index of Afrotropical Encyrtidae
(Hymenoptera: Chalcidoidea). Entomology Memoir of the Department of
Agriculture Republic of South Africa 60: 1-35.
pdf
- Kuntner M, Levi HW. 2006. Nephila hirta, a new synonym of
Eustala fuscovittata (Araneae, Araneidae). Journal of Arachnology 34:
444-447.
- Kuntner M, Agnarsson I, Gregorič M. 2009. Spider eunuch phenomenon
induced by female or rival male aggressiveness. Journal of Arachnology
37(3): 266-271. doi:
10.1636/St08-67.1
- Brooks DM. 2012. Birds caught in spider webs: a synthesis of patterns.
The Wilson Journal of Ornithology 124(2): 345-353. doi:
10.1676/11-148.1
Text by Norman Larsen ©
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