This year, Botswana was lucky enough to receive records amounts of rain. While we welcomed this bountiful surprise, it did put a slight spanner in the works. Water can be devastating for cars, so this unusual season we’ve had to switch to using boats to get around. While this makes for a much more exciting commute, it can be a little traumatic for the spiders that tag along for the ride. Spiders like to weave their webs in the cleared paths left behind roaming animals. This strategic positioning helps them ensnare insects that navigate along nature’s natural roads. Unfortunately, this strategy also comes at a cost. An elephant can wreak havoc for an industrious spider, but if they’re lucky, the elephant will use that track just once a week. They’ll simply gobble up their webs and start afresh. Boats, on the hand, leave behind channels indistinguishable to hippo paths and the NHFU use them on a regular basis. As a result, our boats are always laden down with spiders of every colour, size and fear-inducing capacity. For some of our burliest crew, this can be very traumatic (cough* cough* Steven) but to me they’re fascinating, and there is one spider in particular that deserves some serious respect.
A Golden Orb climbs up its web. These spiders have one of the strongest silks in the world and are coated in a special oil so they don't get ensnared in their own strands. Photo credit: Hannah Gormley.
Over their 165-million year history, Golden Orb spiders have spread from Yemen to South Africa via Botswana. It is one of the largest, most prominent, and, with its striking colouration, terrifying spiders that graces our surroundings. The large black and yellow striped beauties that represent the species are actually the females - you’d be lucky to spot their tiny, drab, maroon male counterparts. The evolution of “female gigantism” is to blame for this impressive size and colouration difference, and the trigger has something to do with their slightly unusual bedroom habits…. (more on that later!). Fortunately, for humans, Golden Orbs will deliver, at worst, a nasty bee-like bite which does no lasting damage. Not so for smaller species. Golden orbs have been recorded ensnaring baby birds, bats and even snakes in their enormous webs (try walk through one of these webs yourself and you’ll understand how strong their strands are). She uses her pedipalps (those scary pincers insects have on either side of their mouth) to puncture holes in her victim, through which she then pumps an enzyme to liquidise its internal organs – a natural spider-shake! What goes around comes around, however. Wasps of the family Sphecidae are Golden Orb specialists – they land on the web and lure her in by imitating a struggling insect. On arrival, she’s poisoned, paralysed, and transported away as live food for their own offspring.
Golden Orbs spend the majority of the day in the 'hub' (centre) of their web. During strong sunlight, they'll hang parallel to the sun so that their swollen abdomen shades their head from the sun. When in shade, she hangs perpendicular. The strand of insect carcasses visible here is her food cache, in case of tough times. Photo credit: Hannah Gormley.
Anyway, back to their sex lives. Multiple male orbs will lurk on the outskirt of a female’s web, waiting for their golden moment. The key is distraction. Sexual cannibalism is a very real threat, so they have two techniques. The first is to wait until she’s feasting on a tasty treat or moulting. The second is to win her over with a nicely wrapped up parcel of grub-goodies. Once the moment is right, he’ll weave a small “sperm web” on the outside of the web onto which he deposits a drop of sperm. He lifts this up with his pedipalps (see above) and carries it towards her. He strums on the outskirts of her web, vibrating his abdomen as he attempts to arouse her and gage her mood before proceeding. In a process that can last up to 15-hours (!!) the romantic male stabs his pedipalp and sperm ball through her stomach. This “mating plug” breaks off inside her in his desperate attempt to stop other males from trying their luck later. After the deed is done, he makes a hasty retreat. If he’s lucky enough to escape with his life, he’ll make a living free-riding on her food on the outside of her web.
Approach if you dare! A brave male golden orb approaches a female. Photo credit: Hannah Gormley.
As the name would suggest, golden orbs are known for their enormous golden webs. No one knows why exactly these evolved, but it has been shown that these extraordinary insects can actively adjust the pigment intensity relative to background light and colours (possibly for catching oblivious bees). Mum deposits onto these webs up to 3000 eggs into a special silk sac. One month later, her spiderlings (yes that is a real word) emerge. Using their fangs to cut through the egg sac, their first meal is their home. Their second is their shed exoskeleton. Their third? Their siblings! To survive this brutal massacre, the survivors must move on to greener pastures. They climb to a high point, let out a fine silk line, then parachute away on a breeze. The tiny babies can travel huge distances, with Darwin noting the arrival of spiderlings on the rigging of HMS Beagles 100km out at sea. Hence the extraordinary success of Golden Orbs. If this small yet mighty creature doesn’t impress you, then I don’t know what will. And Steven, next time you see one, I hope you won’t be so quick to run away in fright!
Blog written by Hannah Gormley