Araneus trifolium          Family: Araneidae
(uh-RAY-nee-us  tri-fohl-EE-um)
Common name: pumpkin orb weaver spider; shamrock orb weaver spider
Adult size: 
excluding legs: 0.8 inches (2 cm)
including legs: 1.5 – 1.75 inches (3.8 – 4.5 cm)
Life cycle: one generation per year
Type: beneficial   

Description: Abdomen colour of the pumpkin spider is variable…white, yellow, orange or brown. No matter the colour, there is a smattering of small white dots marking their back and several dark round indentations. Another distinct identifying feature are the white and brown bands on their legs. They also have bristles running the length of each leg, as well as a third claw on their “foot” which helps them manipulate their silk as they are weaving and to walk across their web. These spiders have the trademark number of eight eyes…two rows of four…but their vision is surprisingly poor.

Females are quite a bit larger than males, as is typical in other spider species. The abdomen of the female is spherical growing larger as she nears time to lay her eggs. Come mid-September, the female lays anywhere from several hundred to a thousand eggs in one or more egg sacs or cocoons, roughly 3 cm (1.2 inches) wide. These cocoons are often called a bower, or a retreat, and can be found roughly one metre (39 inches) off the ground…typically made up of seed heads or grass strands woven together with the spider’s silk. The female will guard her eggs until the winter temperatures eventually drop low enough to kill her. The eggs over-winter in their bower and tiny spiderlings emerge in spring. Each spiderling is capable of spinning a tiny replica of its parents’ web.

Pumpkin spiders prey on insects, usually paralysing whatever gets caught in their web with a toxic bite and then wrapping it for eating it later. If the insect is itself venomous, the pumpkin spider will wrap it first and then paralyse it with its bite.

Special Notes: Native throughout much of North America. They are not often seen in spring due to their small size upon hatching. However, as they grow, particularly the larger females, they are spotted more frequently in late summer and autumn. Beneficial insect for pest control.

While the pumpkin spider’s bite is toxic to insects, it is rarely of consequence to humans. The exception is those people who have more sensitive immune systems or sensitive skin.

In our Zone 7a garden: The cross orb weaver spider, Araneus diadematus, is much more common in our garden but every now and again a pumpkin spider appears sometime in August. Most recently, a female appeared at our compost bins mid-August 2017. She, or another female pumpkin spider built a bower in a few strands of our silver maiden grass, Miscanthus sinensis var. canadensis ‘Cosmopolitan’ in the second week of September. The female remained on guard of her eggs until the first week of October when the temperatures dipped to 0.5 °C (32.9 °F) and -1.0 °C (30.2 °F) two nights in a row.

Note: The camera lens cap next to the female pumpkin spider gives some representation to her size. The lens cap is 2 inches (5.2 cm) across.

Posted on October 11, 2018