By Maggie Chen
Fall is officially underway and along with heralding all things mysterious, we want to shine a light on one of our watershed spider residents: the Cross Orbweaver. While we are giving some shine on the Orbweaver, those in the Bay Area might see some early Halloween decorations as baby spiders are falling from the sky! Bay Area residents have shared on social media seeing tufts of white spider webs floating around and sticking to surfaces in San Francisco, Danville, Gilroy, and more.
Within these webs are baby spiders that are looking for new places to live – this process is called ballooning or kiting. Baby spiders weave strands of silk to catch the wind in order to disperse and move away from their siblings so they are not competing with each other. By the time you see the tufts of the web, it is likely that the baby spiders are gone and have already left the threads. The dispersal process could be compared to dandelion seeds blowing away in the wind.
Misunderstood by mass media and painted as another scary insect, these garden helpers are one of many integral residents in your garden! Their Indigenous Chochenyo name is Tirasmin though they are also known as the European Cross Orbweaver Garden Spider. The name suggests they were introduced from Europe to North America and are known for their unique (and namesake) white cross-shaped markings on their abdomen.
Though they are small– the females are almost twice as large as the males, a mere 0.80 inches in body length compared to the males’ 0.50 inches–the Cross Orbweaver is mighty. As tiny garden carnivores, they snack on insects like flies, mosquitoes, moths, and other smaller insects. After the insects are caught in their web, the spider immobilizes them with its venom before consuming them. The initial bite paralyzes their prey and also minimizes the danger of the spider getting stung or bitten. Their prey is quickly wrapped in silk and may hang on the web to be stored for consumption later.
They are reclusive creatures (so relatable) and are not harmful to humans or native spiders. They create new webs every day, sometimes as wide as 2 feet in diameter! As the main character of their own web, they tend to sit in its center to reach any tangled insects quickly. If it feels threatened they may shake their webs to startle the threat to hopefully make the threat leave — the web shaking would make the spiders look like a blur and this could be a reaction to confuse potential predators too. If the predator does not leave, the spider will drop to the ground and return to its web’s center when it feels safe again.
Cross Orbweavers have a lifespan of around one to two years. After mating, females can lay between 300 to 800 eggs in a sac they protect until the egg hatches. The spiderlings themselves disperse after hatching to build their own webs and continue the species’ life cycle.
The Cross Orbweaver is one of many residents in our Wildcat Creek Watershed, read more about them as a part of our North Richmond Urban Nature Loop which connects people to local nature. And let us know if you spot them as one of the 10 illustrated sidewalk stickers along Giarmita Street from Verde Elementary to Shields Reid Park!