Bug FAQNorthern Rat Flea
Nosopsyllus fasciatus · Order: Siphonaptera · Family: Ceratophyllidae
Also called: Rat Flea, a rat flea, flea
Source: Wikipedia
Nosopsyllus fasciatus is a small (3-4 mm) flea that lives on rats, mice and occasionally humans. It is a known vector of plague and can also transmit the rat tapeworm Hymenolepis diminuta.
Source: Wikipedia
How to recognize it
It has a flattened body, well-developed eyes, a rounded head, and a long dorsal bristle with a short ventral bristle on the head.
Source: Wikipedia
Size
Adults measure about 3 to 4 mm long.
Source: Wikipedia
Is it a pest in the house?
It commonly infests domestic rats and house mice found in homes. Besides spreading plague, it can host the rat tapeworm Hymenolepis diminuta in several continents.
Source: Wikipedia
Does it bite or sting?
The flea can bite humans, though it prefers rodents. Because it can transmit plague and murine typhus, its bite is a health concern.
Source: Wikipedia
Where it lives
It lives worldwide because it depends on rodents and other mammals for survival.
Source: Wikipedia
What it eats
Adults bite rodents and can also bite humans, while larvae feed on other adult fleas or injured hosts.
Source: Wikipedia
Life cycle
The flea goes through three larval instars before becoming an adult. Each molt requires partial replacement of digestive cells.
Source: Wikipedia
When you see it
Infestations peak in summer when rodent activity is highest and drop in winter.
Source: Wikipedia
Where it comes from
It originated in Europe and is the most widely spread species of its genus.
Source: Wikipedia
Lookalikes
It looks similar to other species in the Nosopsyllus genus, which contains many taxa.
Source: Wikipedia
Where it is found in the US
Recorded in 26 of 51 states and DC. Most records: Utah, Alaska, Hawaii, Massachusetts, Idaho, Washington, Ohio, Oklahoma.
Darker = more records. Counts are museum and citizen-science records, not population size.
Source: GBIF
Status: introduced in Canada. Source: iNaturalist
Months it is reported in the US
Source: GBIF
More photos
.jpg){kind=link}
.jpg){kind=link}
Questions people ask
Can northern rat fleas bite humans?
Yes, they can bite people, although they more often feed on rodents.
Source: Wikipedia
Do they spread disease?
They are vectors of plague and can also carry the rat tapeworm Hymenolepis diminuta.
Source: Wikipedia
When are infestations most common?
Infestations are highest in the summer months and decline during winter.
Source: Wikipedia
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Nosopsyllus_fasciatus
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-23 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-23.