Thermobia domestica (Packard, 1873)

Firebrat

The silverfish's heat-loving cousin, it lives where your furnace lives.

Order: Zygentoma
Family: Lepismatidae
Group: Silverfish, firebrats & booklice
Ontario status: Established, near heat sources: furnace rooms, bakeries, boiler rooms

Why it matters

A minor nuisance that damages stored paper and dry goods near heat sources, and a useful indicator that a hot void is undisturbed and unsealed.

Origin

Probably tropical regions originally; spread with heated buildings.

Behavior

Same shy nocturnal habits as the silverfish, but it wants heat, it lives where the house is warmest and eats the same starches.

Living conditions

Furnace rooms, boiler rooms, hot-water tank closets, bakeries, and the warm voids around heating pipes.

Signs of presence

Mottled gray-brown fish-shaped insects near the furnace or hot-water tank
Feeding damage on stored paper or pet food kept in warm utility rooms
Sightings at night when the furnace room light comes on

Weaknesses

Needs sustained warmth, cool the void and it cannot thrive
Same slow reproduction and fragility as the silverfish
Cannot fly or jump; confined to its hot microhabitat
Sealing pipe chases and decluttering utility rooms removes its world

Myths and facts

Myth Firebrats start fires or damage heating equipment.
Reality They just enjoy the warmth, they damage paper and dry goods near the heat, not the equipment itself.

Research notes

Morphology

Body 10-15 mm; mottled gray-brown (never silvery); fish-shaped; three caudal filaments; long antennae. The mottling is the quick field separator from silverfish.

Diagnostics

Mottled gray-brown zygentoman found near heat sources (furnace, hot-water tank, bakery ovens). Temperature context is itself diagnostic.

Easily confused with

Silverfish (Lepisma saccharina) Silverfish are uniformly silvery and cool-damp dwellers; firebrats are mottled and found near heat.

Life cycle

Adult: Adults live 2-5 years
Egg: Eggs laid in cracks near heat; hatch in ~2 weeks in warmth
Egg to adult: 2-4 months in its preferred heat
Generations per year: Overlapping; continuous
Nymph or larva: Nymphs miniature mottled adults; many molts

Development

Ametabolous like the silverfish, direct development, lifelong molting. Faster than silverfish because of the heat it lives in.

Reproduction

Same primitive indirect sperm transfer as silverfish; ~100 eggs per female lifetime.

Distribution

Global: Cosmopolitan in heated structures
Native range: Probably tropical Old World
Ontario: Indoor populations near heat sources province-wide

Ecology

Thermophilic detritivore, thrives at 30-40 °C near furnaces, boilers, and commercial ovens. Feeds on starches, book bindings near hot pipes, pet food. Nocturnal.

Resistance

Unknown, managed physically; no documented resistance.

IPM implications

Same playbook as silverfish, relocated to the hot zone: inspect furnace rooms and pipe chases, seal gaps around hot pipes, store susceptible materials away from heat sources. Monitoring traps placed near heat. Its presence maps hot, undisturbed voids.

Chemical ecology

Unremarkable chemically, like its cousin. Distribution is driven by temperature preference, not chemistry, it is one of the most heat-tolerant indoor insects.

Genetics and DNA

No reference genome published as of 2026.

Taxonomy

Order Zygentoma, family Lepismatidae. Authority (Packard, 1873). The thermophilic counterpart to Lepisma.

Open questions

Thermal tolerance physiology; why it remains less common than silverfish despite similar ecology.

References

Ebeling, W. (1978). Urban Entomology, University of California, Riverside.