Our Biggest Spider: Argiope Aurantia

Our Biggest Spider: Argiope Aurantia

Story and photo by Tammy MacKenzie

Say “spider,” and most people picture a large hairy tarantula or an orb weaver sitting in the centre of its large round web.

We don’t have any tarantulas in Ontario, but we do have more than one hundred species of orb weaver. They range in size from 2 to 25 mm in body length and come in a vast array of colours and patterns. They also live in a great variety of places, from low grasses to tree-tops.

Our largest species is Argiope aurantia, commonly known as the black and yellow garden spider, for obvious reasons: the outstanding colouration, and habitat preference for open areas of tall grasses, flowers, and shrubby plants that will support webs that can be up to 60 cm across. They are commonly found in fields, roadsides, and yes, gardens.

It takes many months for these beautiful spiders to reach their full size, so they are most commonly spotted in later summer into fall, on their large orb webs with the distinct zig-zag line running vertically through the centre. This is called the stabilimentum, and while there are various theories as to its purpose, it’s not truly known what it serves. It may be to keep large animals or birds from going through the web, to attract insects, or to help camouflage the spider.

Smaller juvenile spiders may create a stabilimentum that spirals around the centre of the web.

Male Argiopes are considerably smaller than the females, only one quarter of their size, and will build a small web along the female’s, or hang out on hers while courting her. The male will pluck at strands of the web to attract the female’s attention and gauge her willingness to be courted. If she is willing, he will deposit sperm packets on his pedipalps (small leg-like appendages at the front of his body) into her epigyne (external sex organ on the underside of the abdomen).

While males may occasionally be eaten by unreceptive or hungry females, they most commonly die soon after reproducing, as they have shorter life spans than females.

Females will produce one or more golf-ball sized egg sacs secured to grasses or the side of a tree or building. The hatchling spiders will stay inside the egg sac throughout the winter and emerge in the spring.

These beautiful spiders should be welcome in our gardens, and admired. They may be of impressive size, but eat a lot of insects, and have no interest in us, except as a threat to themselves they would always flee from if possible.

When they feel threatened by something approaching, they may oscillate their web by flexing their legs to make it sway rapidly back and forth, or drop to the ground to hide in the thicker vegetation. They would only bite if grabbed and physically threatened by pressure against their bodies, and even then may not envenomate, as venom is a costly resource needed for their food. Bites are said to be similar to a bee sting in their affect, and are of no medical concern to us. 

Tammy MacKenzie lives in Tay Valley Township, Lanark County. They have been interested in spiders, among other creatures, since childhood. Photographing and learning about spiders has been a passion for the past 12 years or so.

Tammy is the owner/admin of Facebook groups Spiders of Ontario and Quebec and Spiders of Atlantic Canada. They also help admin several other spider groups and is member of many other arachnid and/or insect groups. They have developed an expansive network of friends and contacts in the world of arachnology over the years.

Tammy has been involved in spider education for more than a decade, presenting at “bug day” events in local elementary schools. Their passion for these fascinating creatures fuels the desire to help other people learn about them and especially to overcome fears.

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