Can fall pests move between apartments?

The accurate version of "can pests move between apartments" has two parts, and conflating them is where most of the folk anxiety comes from. Part one, true: dormant adult insects that entered the building's exterior the previous fall can travel through shared wall cavities, soffit runs, and common attic space, and emerge into a unit that isn't the one nearest their original entry point. Part two, false: none of this is an infestation spreading from unit to unit the way, say, bed bugs or cockroaches can. Cluster flies, stink bugs, lady beetles, and boxelder bugs do not reproduce indoors — they are in diapause, a dormant state, waiting out the winter. There is no growing population moving toward you; there is a fixed number of insects that entered the building months ago, redistributing themselves through connected voids as they occasionally reactivate on warm days and wander toward light.

A single-family house has one continuous envelope, but it's also one household's problem to seal. A multi-unit building often has the same continuous soffit, ridge vent, and attic running the length of several apartments, plus shared utility chases for plumbing and wiring that thread between units. UK Entomology notes that sealing gets progressively harder on taller, more complex multi-story buildings — there are simply more penetrations, more shared cavities, and more places an insect can wander before it finds daylight. That's the mechanical reason a top-floor unit under a shared attic, or a unit sharing a chimney chase with its neighbor, tends to see more activity than a ground-floor unit with a simpler, more isolated envelope.

The candid split here matters more than the general advice to "seal your home," because a renter's leverage is really limited. Inside your own unit, sealing gaps around baseboards, switch plates, ceiling fixtures, and window and door frames is a real, homeowner-scale (or renter-scale) fix that stops insects from finishing the last few inches of their journey into your living space. It does not, and cannot, stop insects from being in the building's shared cavities in the first place — that requires exterior exclusion (caulk, screening, sealing utility penetrations) across the whole building envelope, done before the fall entry window closes in early-to-mid September, which is a property-management decision, not a tenant one. If activity is heavy and building-wide, raising it with the landlord or management company as a timed, late-summer exterior job is the practical next step — not a lease dispute, just a maintenance request with the right timing attached.