Which ones are they?
Québec is home to nearly 700 spider species, grouped into 27 families. Towards the end of summer, spiders of the Araneidae (orb weaver) family are the ones we notice most. The species in this family spin orb webs out of silk to trap their prey. Of these, garden spiders (Argiope spp.), and other orbweavers (Araneus spp and Larinioides spp.) are the most common. Females have particularly long legs and a large abdomen. Males are much smaller and can easily go unnoticed.
These large spiders stay in their webs all day facing downward. If disturbed, they can become frantic, causing the web to vibrate and making them less visible. Garden spiders are mostly found in damp areas, whereas species within genera Araneus and Larinioide spin their webs on man-made structures such as bridges.
Why are there so many?
In spring, the young orb-weaver spiders leave the egg sac that was spun by their mother the previous fall. They don’t reproduce in summer but feed and grow larger by molting several times. Even though they haven’t yet reached their maximum size, these spiders are already voracious predators that will feed on almost anything that gets trapped in their web: mosquitoes, bees, moths, etc.
Why do these spiders want to be close to our homes? They spin their webs where prey is abundant, such as near water or in damp areas. In the city, you’ll often find webs around outdoor lighting, which attracts numerous nocturnal insects.
Spiders reach their final development stage at the end of summer, in late August. During this stage, orb-weavers attain their maximum size and their sexual maturity. So there aren’t more spiders in August—they’re just bigger and more noticeable. This is especially true in areas where prey is concentrated, such as near light fixtures. In fall, the abdomens of pregnant females grow especially large. They lay their eggs in a silk sac, which can contain hundreds of eggs. The baby spiders will spend winter in the egg and leave the sac the following spring.
Are they dangerous?
Not at all! At least, not to humans! Although the vast majority of our spiders are venomous, they mainly use their venom to neutralize and digest prey. They may bite humans if they feel threatened (for example, if they get caught between your skin and clothing, or if you handle them roughly). In fact, around the world, those species whose venom poses the greatest risk to humans make up only 0.5% of all known spiders. None are found in Québec!
Spiders are largely beneficial to us. They help control the arthropod populations they feed on, as well as being fascinating creatures!