Nosopsyllus fasciatus
northern rat flea

Although northern rat fleas (Nosopsyllus fasciatus) are native to Europe, they are commonly found worldwide due to the commensal relationship of their rodent hosts to humans. The first northern rat fleas identified in the United States were found in Mammoth Cave, Kentucky and Ames, Iowa before 1900 and quickly spread to ports and large cities. They are more common in the northern United States and although they can still be found in the south, the populations are significantly lower. In warm temperate regions N. fasciatus together with Xenopsylla cheopis make up the majority of the flea population on rats. (Chick and Martin, 1911; Crooks, et al., 2004; Pratt and Good, 1954)

Since N. fasciatus is an obligate nidiculous parasite on vertebrates, its habitat is determined by the needs of its host. This flea is not host specific and when given the opportunity will jump to other nearby animals. Nosophsyllus fasciatus is usually found on rats but will sometimes transfer to other rodent species or small vertebrates. When on rat hosts adult fleas prefer to feed on the sacral and pelvic regions and rarely move towards the anterior of the rat. The larvae live in the nests of their hosts but are sometimes found with the adult fleas in the host’s fur for feeding. While off the host, both the larva and adult survive best in slightly damp piles of rubbish where it is cool and humid. (Crooks, et al., 2004; Iqbal and Humphries, 1982; Molyneux, 1967; Strickland, 1914)

Nosophsyllus fasciatus has a holometabolous life cycle, including the stages of egg, larva, pupa, and adult. The eggs are small (about 0.6 mm), white, translucent, and slightly sticky. Active larvae are similar to small caterpillars with 13 segments. Pupae are usually, but not always, inside of a sticky cocoon made by the larvae. (Strickland, 1914)

Adult N. fasciatus range from 1 to 9 mm in length. They are laterally flattened, have backward-pointing bristles on their bodies, and usually have two sets of ctenidia (genal combs on the head and pronotal combs on the first thoracic segment). All of these features allow the flea to move around rapidly in fur in a forward direction but prevent it from moving backwards which helps prevent the host from removing it. Fleas are built for jumping long distances with powerful rear legs, pleural arch (with the energy efficient elastic protein resilin), and skeletal locking mechanism. Fleas have simple eyes (ocelli), short antennae that lie in grooves on their heads, and seven abdominal segments of which the last three have developed into reproductive organs. Fleas are sexually dimorphic. Males are distinguished by their long penis rods coiled within the abdomen. Females can be identified by their lack of penis rods and the presence of a kidney shaped organ called the spermatheca which stores sperm from the male. Nosophsyllus fasciatus is unique because in females, the posterior ridge of the seventh sternite has a sinuous outline and in males the movable finger of the clasper is planoconvex, short, and broad. Adult rat fleas are distinct because members of their genus have well-developed eyes and pronotal combs. (Askew, 1971; O'Toole, 1995)

Like all fleas, N. fasciatus has a holometabolous life cycle and undergoes metamorphosis. External conditions determine when the eggs hatch, and they will no longer be viable if hatching is significantly delayed. The eggs tolerate temperatures of 5 to 29 degrees Celsius, and under these optimal conditions will hatch after 7 days. The larvae survive best in dark areas with low temperature, high humidity, and rubbish in which they can hide. The larval stage lasts 60 days on average. They spend about 17 days developing in the pupal state and emerge at slightly different stages of maturity depending on the lifestyle and diet of the larvae. The fleas can remain in the pupal stage for many months and will not emerge at low temperatures. Total development from egg to adult averages 84 days. (Askew, 1971; Iqbal and Humphries, 1970; Rothschild and Ford, 1973; Strickland, 1914)

Fleas reproduce sexually, and will mate year round. They mate randomly when there is accidental contact between males and females after feeding on the host. Currently there are no known methods for finding mates, mating rituals, or mate defense. (Iqbal and Humphries, 1970)

In fleas, mating occurs soon after the adults emerge from the pupal stage. Copulation usually takes place off of the host, and appears to happen accidentally when fleas of the opposite sex come into contact with each other. The male clasps the female with his antennae and they join genitals for two to three hours. A contact-chemical from the females stimulates receptors in the male maxillary palps. (Iqbal and Humphries, 1974)

There has been much debate about whether or not northern rat fleas need to take a blood meal before mating. Iqbal and Humphries observed that mating only took place if both sexes had fed. They hypothesized that mating was triggered by the rise in temperature experienced while on the host and found that mating occurred between unfed fleas at 30°C to 35°C or at room temperature in fleas that had previously been exposed to such temperatures. Rothschild and Ford concluded that mating behavior can differ based on strain and that this difference may be due to the different hosts used to raise the fleas, different rearing techniques, or the quality or amount of food they had access to. (Iqbal and Humphries, 1970; Rothschild and Ford, 1973)

Females lay eggs off of the host after a bloodmeal and leave them to develop freely. There is no parental care. (; O'Toole, 1995; Russell, 1913)

When fed regularly on blood northern rat fleas are healthy and able to reproduce continuously for months, but if the flea does not have constant access to food, then its survival depends on its environment, especially the presence of rubbish to hide in. With sufficient rubbish at 60° F and 70% humidity fleas that are not well-fed can live for 17 months or longer, but at 70° F and 45% humidity they will only live about 4 months. Without rubbish their lifespan is significantly shorter and not affected by temperature or humidity. (Strickland, 1914)

Fleas are not social animals and only live near each other in order to have access to the host and its nest. All fleas are powerful jumpers and use this ability to land on their hosts. When fully gorged a flea is able to jump about three inches and when empty about four inches. (Rothschild and Ford, 1973; Strickland, 1914)

The rat flea does not stray from the nest of its host.

Because fleas have very reduced eyes, they rely on two main sensory organs. The first is their antennae which they use to detect air currents, vibrations, touch, and smells. The second organ is the pygidium, a plate covered with hairs at the back of the ninth abdominal segment. It is used to sense air currents which aid in locating a host. There are two steps to host perception: getting to the host, and deciding whether to stay on the host once it has landed. Olfactory senses likely allow the flea to sense the host from a distance. Host body temperature is the determining factor in the flea’s decision to leave the host because if it falls below normal, the flea will think the host is dead. (Iqbal, 1974; Russell, 1913)

Flea larvae are usually nidicolous parasites, living in the nest of the host and feeding on feces of adult fleas which contain blood that has not been completely digested. The larvae of northern rat fleas, however, also use their mandibles to attach themselves to the pygidial (anal) area of adult fleas so that it can feed directly on the feces of the adults, and if an adult flea is injured the larvae will attack the adult. One experiment showed that when given the choice between rat feces and dried blood the larvae do not prefer one over the other. Northern rat fleas will feed on humans and small animals like rabbits and mice given the opportunity, however, fleas that feed on hosts other than rats are not able to lay eggs. (Chick and Martin, 1911; Molyneux, 1967; Strickland, 1914)

Adult fleas have specialized sucking mouthparts that they use to feed on the host's blood. These include a pair of serrated laciniae to penetrate the skin and a single epipharynx to suck up the blood. Once the blood enters the flea's digestive tract it enters the proventriculus, an area of the gut that has sclerotized teeth to break up individual blood cells. (Iqbal and Humphries, 1982; Russell, 1913)

Nosophsyllus fasciatus will stay on its host and feed for two to three hours, because although it has the ability to take a full meal in ten minutes, finding a suitable blood vessel (the larger the better) and being disturbed by host activity prolong feeding. Females always take larger bloodmeals than males (about nine times more) because they excrete more blood after feeding and need to provide nutrients for eggs. On rats, fleas prefer to feed on the sacral and pelvic regions and rarely move towards the anterior of the rat. To feed, fleas insert their serrated laciniae into the host’s skin. (Iqbal and Humphries, 1982)

Many flea species such as cat fleas (Ctenocephalides felis felis) have insect predators including ants, beetles, and nematodes. Nosophsyllus fasciatus likely has similar predators, though specific species have not been identified. (Rust, 1997)

Nosophsyllus fasciatus is a parasite of rodents and other mammals, including humans, and most importantly, is a disease vector. Trypanosoma lewisi is one parasite transmitted by northern rat fleas. Rat hosts can be infected by eating the blood or organs of other infected rats, by eating their own fleas that have fed on an infected rat, or by being bitten by an infected flea (most common). The bacteria Salmonella enteritidis is also spread by northern rat fleas. The infected fleas have a shortened lifespan, but are more efficient vectors than other vector species such as Xenopsyllus cheopis. Humans can contract salmonella by being bitten by infected fleas or by eating food contaminated with feces from infected fleas. (Eskey, et al., 1949; Minchin and Thomson, 1911)

Northern rat fleas have no positive economic importance for humans.

Athough N. fasciatus uses rats as primary hosts, it also feeds on humans when necessary. In one experiment, Chick and Martin starved northern rat fleas and then allowed them to sit on either humans or rats, both of which they feed on readily. Some, but not all, human subjects used in the experiment experienced irritation and swelling from the flea bites. It is highly likely then that fleas able to transfer diseases in rodents can also transfer them to humans when they feed. Like Xenopsylla cheopis, northern rat fleas can also be vectors of Yersinia pestis, or plague. Other human diseases this species can spread include salmonella caused by Salmonella enteritidis and sleeping sickness caused by Trypanosoma lewisi. (Askew, 1971; Chick and Martin, 1911)

Northern rat fleas are not endangered in any way and have no special conservation status. Their host populations are abundant and widespread, and thus the species likely has little risk of endangerment.

Nosophsyllus fasciatus is commonly known as rat fleas or European rat fleas.