Bug FAQNorthern Rat Flea
Nosopsyllus fasciatus · Order: Siphonaptera · Family: Ceratophyllidae
Also called: Rat Flea, a rat flea, flea
Source: Wikipedia
The northern rat flea is a 3-4 mm elongated flea that commonly lives on rats and mice and can also bite humans. It is a known vector of plague and murine typhus and can carry the rat tapeworm Hymenolepis diminuta. Infestations peak in summer when rodent hosts are most active.
Source: Wikipedia
How to recognize it
It has a laterally flattened body, well-developed eyes, a rounded head, and a distinctive short bristle just below a long dorsal 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 is found on rats and mice that live in homes and can transmit plague and murine typhus.
Source: Wikipedia
Does it bite or sting?
The flea can bite humans, though it prefers rodents. Because it can carry plague and murine typhus, its bite is a health concern.
Source: Wikipedia
Where it lives
It lives on domestic rats and house mice and can be found together with other parasites on the same host.
Source: Wikipedia
What it eats
Adults feed on the blood of rodents and can also bite humans. Larvae attach to adult fleas or feed on injured hosts.
Source: Wikipedia
Life cycle
The flea goes through three larval instar stages before becoming an adult. Each molt requires partial replacement of digestive cells.
Source: Wikipedia
When you see it
Infestations are most common in summer and decline in winter.
Source: Wikipedia
Where it comes from
The species originated in Europe and belongs to a genus native to the Palearctic realm. It now has a worldwide distribution because it travels with rodents and other mammals.
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
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Questions people ask
Do they bite humans?
Yes, the northern rat flea can bite people, though it mainly feeds on rodents.
Source: Wikipedia
What diseases can they spread?
They are vectors for plague and murine typhus and can also host the rat tapeworm Hymenolepis diminuta.
Source: Wikipedia
When are infestations most common?
Infestations peak during the summer months when rodent activity is highest.
Source: Wikipedia
Sources
- Wikipedia: https://en.wikipedia.org/wiki/Nosopsyllus_fasciatus
Look it up elsewhere: GBIF · iNaturalist · BugGuide · ITIS · Wikipedia
Text written 2026-10-24 from the sources above and checked sentence by sentence against them. Data fetched 2026-10-23.