Spiders (Araneae) live by catching and sucking other animals dry. For stabbing and killing their prey, they have a set of chelicerae (jaws).The edge of the jaws is a curved, hollow hook, through which venom from the venom gland can be squeezed into the prey.
Spiders’ venomous fangs are almost never used as defense weapons. If the fangs end up in human skin, it is highly unintentional and can only happen if a person holds the animal by hand or it gets trapped under their clothing. Even in these cases only the largest of the Danish species can bite in such a way that it is felt. One example is the domestic house spider, Tegenaria domestica, and the cross spider, Araneus diadematus – two major species which are known to live in and around most Danish homes.
Bites from large spiders can cause intense swelling, which can last for a long time. A spider bite, which a person might have gotten in bed while sleeping, may be a possible explanation for such, local swelling.