Certain insects have specialized feet that enable them to defy gravity and walk in places that seem to be impossible to cling to. Stiff hairs, natural adhesives and large claws all come into play to enable the insect to walk on smooth, upright or upside-down surfaces.

Flies need sticky feet to walk on ceilings, but not so sticky that they get stuck upside down. So each foot comes with a pair of claws that help hoist the gooey foot off the wall. Flies use several different techniques to get unstuck: pushing, twisting, and peeling its footpads free.

It is practically impossible to kill enough of them to make a difference once they have found their way into wall voids, ceilings voids and attics. Once they’re in, they’re in and there is not much we can do about it. When temperatures warm in the spring, the flies attempt to find their way back outside to lay eggs.

They have pads on their feet covered with tiny hairs that continually produce a sticky glue-like substance which keeps them stuck to the wall and then peel it away with each footstep and this is true of many insects (reference), so they don’t have to consciously know that they’re going to climb up a wall before they …

Why do bugs always seem to die on their backs? This is a matter of physics. As the bug nears death, normal blood flow ceases, causing the legs to contract inwardly. Without the support of the legs, the body becomes top-heavy, and usually falls upside-down.

When daytime temperatures are warm enough for them to become active but nighttime temperatures become too low, they search for a cozy warmer crevice to rest. If your windows leak even small amounts of warm air, these invisible thermal plumes attract the insects, who follow the gradient to its source.

A housefly will likely die on its own from stress. If you’ve ever seen a fly bouncing on a window trying to escape, that’s what will eventually cause its death. These flies aren’t meant to be in air conditioned environments, which can also contribute to them dying.

Houseflies use light as a means of orientation, depending on light from the sky in particular, to navigate. Houseflies tend to move toward sunlight, so they will collect around doors and windows. Flies caught in a window may be somewhat disoriented.