Silken threads from which spiderlings balloon away from their egg sac.
Image: Robin Darroch
Source: Robin Darroch
Question: Recently in Hamilton Victoria, the sky was absolutely filled for as high as you could see (with binoculars) of floating streams of spider webs containing tiny spiders. The trees, fences and grass were covered in them. It’s common here during Autumn but I've never seen it like this. Please advise the species of spider and explain this amazing event. Where do they come from? How do they get airborne?
Answer: The summer just gone was the best season for orb-weaving spiders in at least a decade. The warm, wet conditions in South-Eastern Australia promoted plant growth, and the conditions were perfect for insects to breed in large numbers. These conditions are also good for spiders, and the number of insect prey around meant there was plenty of food for them. Many of those spiders have now died off as the weather starts to cool, but they have left behind a bountiful supply of egg sacs, some of which are starting to hatch. Depending on the species, egg sacs may contain 200 or more eggs.
Most spiderlings balloon away from the egg sac on silken threads, lifted into the air by the slightest breeze. And they are light enough to be taken by winds into the upper atmosphere, dispersing for hundreds of kilometres. When they land, the silken thread sticks to the nearest object and the spiderlings begin building a tiny web. The only spiders that don’t disperse this way are trapdoors, funnel-webs and tarantulas. There are more than one hundred species of orb-weavers in Australia, so spiders you see are a combination of these species, but the two most common in South-Eastern Australia are the Garden Orb-weaver (Eriophora transmarinus) and the Golden Orb-weaver (Nephila edulis).
We have also had some amazing observations of this phenomenon this week from a pilot, demonstrating how high and how far these spiderling strands of web can go. On approach into Mount Gambier, at a height of about 2000ft, he spotted long floating “clumps” of silk-like material, getting more numerous towards the ground. On landing, he took some photographs of these clumps on the runway, plus a photograph of an example of numerous spiders around the airport. You can see the photographs he took by clicking the gallery on the right side of this page.
The clumps are quite thick, but appear to be masses of fine silk tangled together. This was probably produced by hundreds, if not thousands, of silken strands produced by tiny spiderlings. They clump together in the wind and would easily be picked up by passing objects, such as aircraft. Given the number of ballooning spiders observed throughout Victoria in the last few weeks, it’s no surprise that these masses of web are present both in the air and on the ground.
The spider in the photograph is a Wolf Spider; Wolf Spiders do also disperse as spiderlings by ballooning, but that particular spider is too old to be ballooning. Wolf Spiders are particularly common in grassland, and that specimen may have arrived there by ballooning sometime in the past.