Inter-dimensional beings that resemble enormous insects are creatures which exist in a dimension parallel to ours. A device created by the Ancients and discovered among the ruins on P9X-391 has the ability to make these beings visible in our own dimension. The creatures seen on Earth are probably native to this planet, but we have always been unaware of them since they exist in a dimension that does not allow us to interact with them. They are not considered dangerous, however civilian panic over the ability to see them is a concern. When the effects of the inter-dimensional device spread beyond the SGC, causing civilians to see enormous insect-like creatures, Hammond ordered the immediate containment of Colorado Springs and the surrounding area as far as Piedmont Hawthorne Airfield in Hawthorne County. The National Guard was called in and the community was quarantined using the cover story of an accidental spill of an experimental chemical that can have a hallucinogenic effect. Once the situation was contained, a placebo pill was used as the antidote effect was spread to the community.
Because there was no physical contact with the insect creatures from a parallel dimension, they were not considered to be a threat, unlike parasitic leech-like creatures which were able to cross into our physical dimension when caught in the subspace field of a modified Sodan cloaking device. These inter-dimensional parasites burrowed into indigenous host animals and posed a significant danger to the surrounding community. There is no clear evidence that the two kinds of inter-dimensional creatures inhabited the same dimension.
Episode Reference: Sight Unseen