Big female, tiny male!
On a recent walk through one of the coastal forests I came across this amazing example of ‘sexual dimorphism’. This is where there are striking differences in size, shape, colour and other features between males and females of the same species. In this case it is a striking example of size-based sexual dimorphism with a gigantic female and a puny dwarf male.
Orb-weaving spiders are common in the coastal forests – among the more striking are these magnificent Nephila, who hang their massive webs, often over a metre in diameter, along forest paths. These spiders are incredible creatures. They are not just large and colourful (this one here was about 7 inches from toe to toe!), but also highly intelligent.
I have actually seen some of them gather up their webs when they see a person or a large animal approaching. After you’ve passed, they drop the web back down into place. This means that the spider doesn’t have its web snagged every time some large bumbling mammal walks by.
While taking a closer look at the spider’s magnificent web and beautiful colours, I noticed that there was another creature clinging to the web beneath her. On closer inspection I realised that this was a male. These Nephila spiders have really tiny stunted males in many species.
The reason behind this is thought to be female aggression. The female Nephila are famously aggressive (even as I watched her from a safe distance she rotated her fangs at me like a pair of macabre bicycle pedals!). Males have gotten smaller and smaller through evolution so that they can sneak into the webs and mate with the females without getting eaten.
Males do compete for access to females, and therefore there is a trade-off: you need to be big enough to fend off the other boys, but not too big or else the female will notice you and take you for an intruder and despatch you before you can mate with her!
In many cases the males still get eaten after they mate with the female. In fact in some spiders the males actually somersault onto the females jaws after mating with her! Notice how in this pair of would-be lovers the male is keeping to the opposite side of the web until the female yields to his charms. Just in case he needs to make a quick escape! Talk about living life in the fast lane!
Many thanks to everyone for the kind comments. More from the wonderful world of bugs soon!