Interdimensional Bugs are a race of non-sapient creatures, similar to gastropods and arthropods, which co-exist with us beyond our dimensional spectrum. Though they do not appear to be directly aware of us, they are capable of walking across objects in our dimensional plane, as well as passing through them entirely. Some species are capable of flight. It may be possible that the bugs are native to Earth, or an alternate dimension version of Earth.
The insects are drawn to an interdimensional visibility device, apparently Ancient in origin. When the device is active, it gives Humans who have come in physical contact with it - or with someone who has - the ability to perceive the creatures. (SG1: "Sight Unseen")