I came across this huge spider on Bunaken Island, in northern Sulawesi. The body must have been about 4 cm long and the legs spanned at least 15 cm, maybe more. It is a golden silk orb-weaving spider (genus Nephila) – also called giant wood spiders – which construct large webs to trap their prey. typically flying insects (e.g. bees, wasps and butterflies) but in some cases even small birds have been trapped and consumed! These spiders, in the suborder Areneomorphae, have superb, pincer-like fangs; which can be seen below the head, in the upside-down position in the photo. The tiny spiderlings can also be seen crawling over the web; they are too small to trigger a response from Mum!
The amazing thing about these spiders is their sexual dimorphism; she is huge; he is tiny! I am not 100% sure, but I think that the male is the small red spider which can just be seen to the right of the large black female in the following photo.
It is not altogether clear why the males are so much smaller, but one hypothesis is that so they can avoid been eaten by the female, who ignores such small fry! However, the males do fight it out among themselves for access to the female and size does matter in these battles. So it seems that there may be competing evolutionary pressures for the males to be large enough to win their fights but small enough not to get eaten (1). Curiously though, if a male does mate successfully with a female, it may be in his own interest to be consumed – now there’s commitment for you – since it can help the success of the fertilization (2) – presumably because the female is well fed! I guess the trick is to get eaten after mating rather than before!
Oh yes, I forgot to mention that they are venomous!
1) and Babette F. Fahey (1996). Sexual cannibalism, competition, and size dimorphism in the orb-weaving spider Nephila plumipes Latreille (Araneae: Araneoidea). Behavioral Ecology 7(2): 195-198.
2) and Mark A. Elgar (2001). Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives. Behavioral Ecology 12(5): 547-552.
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