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ACE Prep · Module 9 of 11

Occasional Invaders

Quick answerUpdated September 24, 2026

What does ACE module 9 cover?

Occasional invaders enter structures incidentally, usually seasonally, and typically do not reproduce or establish permanent populations indoors. Control focuses on exclusion and perimeter barriers rather than indoor treatments.

Key factApproximate exam weight: ~5%.

Reviewed by LTK editorial team

Must-know facts

  • Occasional invaders are pests that enter structures but do not breed or establish indoors. Control = exclusion first.
  • Boxelder bugs: feed on boxelder, maple seeds outdoors. Enter in fall to overwinter. Black with red/orange markings. Control = exclusion, perimeter residual.
  • Multicolored Asian lady beetles (MALB): congregate on south/west-facing walls in fall after first cold spell. Can bite, stain, and release defensive odor. Control = exclusion before aggregation, interior vacuuming.
  • Brown marmorated stink bug (BMSB): invade structures in fall to overwinter. Release defensive odor when crushed. Exclusion is primary control.
  • Millipedes and centipedes: enter from outdoor/damp areas. Millipedes = 2 pairs legs per segment, cylindrical, slow, plant debris feeders. Centipedes = 1 pair legs per segment, flat, fast, predatory. Control = moisture reduction, exterior perimeter treatment.
  • Sowbugs and pillbugs (isopods): require very high moisture, feed on decaying plant material. Pillbugs roll into a ball (Armadillidium). Control = moisture reduction, debris removal.
  • Ground beetles, field crickets, earwigs: enter from outdoors in late season. Exterior perimeter treatment + exclusion.
  • Seed-feeding Hemipterans (e.g., Western conifer seed bug, boxelder bug): attracted to lighted buildings at night — lights can draw them in.
  • Cluster flies: enter structures in fall to overwinter in attics and wall voids. Exclusion and wall-void treatment are most effective.

What the exam likes to ask

  • Asian lady beetles become pests when weather turns cold in fall — attracted by the warmth of buildings.
  • Seed-feeding hemipterans enter homes attracted to LIGHTS at night — not blood, water, or shelter.
  • Millipedes require moisture and decaying organic matter — control starts with landscape/drainage, not insecticides.
  • Occasional invaders do not breed indoors — treating indoors treats a symptom, not the cause.

Field takeaways

  • Exclusion work (caulking, door sweeps, window screens) prevents occasional invaders more effectively than any residual spray.
  • Seasonal timing matters — installing exclusion before fall migration prevents the problem.
  • Vacuuming MALB or stink bugs is more effective than spraying once they're inside — crushing releases odors or stains.

Listen, watch, read

Podcast

Why Occasional Invaders Wander Into Your Home

The environmental triggers that drive occasional invaders — boxelders, centipedes, silverfish, crickets — inside, and how to break the cycle.

Slide deck · 12 slides

Occasional Invaders Diagnostic Guide

View the slides

Module 9 quiz

24 questions. Answer them all, then grade to see the reasoning.

  1. Q1Which step does the most to keep overwintering lady beetles and stink bugs out of a home?
  2. Q2Boxelder bugs gathering on a house in fall usually point to which nearby host?
  3. Q3The primary control strategy for occasional invaders is
  4. Q4Millipedes in and around a structure are most effectively controlled by
  5. Q5In autumn, black bugs with red lines on the pronotum and wing edges gather by the hundreds on the sunny side of a house next to a large maple tree. They are most likely
  6. Q6A large brown bug with flattened, leaf-like widenings on its hind legs flies indoors with a loud buzz in fall. It is most likely the
  7. Q7A shield-shaped, mottled brown bug with light bands on its antennae is crawling on window frames in the fall. It is most likely the
  8. Q8What is the best way to remove multicolored Asian lady beetles that are already inside a home?
  9. Q9A fast-moving arthropod with 15 pairs of very long legs is catching insects in a damp basement. It is most likely a
  10. Q10A gray, segmented, armored arthropod rolls into a tight ball when touched. It is a
  11. Q11Sowbugs and pillbugs are classified as
  12. Q12Tiny gray hexapods that leap when disturbed by using a forked organ under the abdomen are swarming on a wet basement floor. They are most likely
  13. Q13A silvery-gray, carrot-shaped insect with mottled markings and three tail filaments is common around a hot boiler and a bakery oven. It is most likely the
  14. Q14Which kind of damage is most typical of silverfish?
  15. Q15A wingless, hump-backed cricket with very long antennae and legs jumps toward people in a damp basement and never chirps. It is most likely a
  16. Q16Large numbers of field crickets are gathering around a store entrance in late summer at night. Which change will reduce them the most?
  17. Q17Earwigs coming indoors in large numbers usually point to
  18. Q18In spring, tiny red mites with very long front legs crawl over sunny walls and windowsills and leave red smears when crushed. They are most likely
  19. Q19Which long-term step is most often recommended to stop clover mite invasions?
  20. Q20Shiny black, fast-running beetles show up in a garage near outdoor lights at night. They are predators and do not breed indoors. They are most likely
  21. Q21Yellowish-green beetles with a dark stripe along the edge of each wing cover are overwintering in a house shaded by large elm trees. They are most likely
  22. Q22A spider with a tiny body and extremely long, thin legs shakes its loose web rapidly when touched. It is most likely a
  23. Q23Which of these pests is NOT considered an occasional invader, because it normally lives and reproduces indoors?
  24. Q24Swarms of mayflies and caddisflies cover a lakeside restaurant's lit windows on summer nights. What is the most useful long-term step?

0 of 24 answered

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