Once the flea emerges from the cocoon, it will not undergo any further molts, and the only size increase occurs due to swelling of the abdomen after feeding (Dryden, 1989a). To identify the different species of Ctenocephalides spp. the outer appearance of the imagines can be used (see also General Morphology). Key distinguishing features of the two most important species of pets, the cat and the dog flea, have been documented by Soulsby (1982):
C. felis: Both pronotal and genal combs are present; length of head is generally greater than twice the width; first two spines of the genal comb are approximately equal in length. The tibia of all 6 legs is armed with 4 to 5 teeth (see Fig. 1).
C. canis: Both pronotal and genal combs are present; length of head is not twice as wide; first spine of genal comb is noticeably shorter than the second spine. The tibia of all 6 legs is armed with 7 to 8 teeth (see Fig. 1).
Pictural key to Dog and Cat fleas
Shape of head
Shape of head
Spine 1 and 2 of
Spine 1 and 2 of
the genal comb
Both 1st and 2nd spine have the same length
1st spine is half as long as 2nd spine
Number of teeth
Number of teeth
Tibiae of all 6 legs have 4 to 5 teeth
Tibiae of all 6 legs have 7 to 8 teeth
Figure 1: Morphological differentiation of the cat flea (Ctenocephalides felis) and the dog flea (Ctenocephalides canis); original size upper right: 3.0 mm
Host seeking stimuli
After emerging from the cocoon, the flea almost immediately begins seeking a host (Dryden, 1993) searching for a blood meal (Dryden, 1989a). A variety of stimuli attract newly emerged fleas. Visual and thermal factors have been found to be primarily responsible for attraction and orientation to the host (Osbrink and Rust, 1985b). Combinations of different stimuli including tactile stimuli, CO2, air currents and light together with the adult’s age stimulate locomotion and modify the adult’s responsiveness, at the same time limiting environmental interference while locating the host (Osbrink and Rust, 1985b).
Stimuli that failed to elicit an observable response were substrate vibrations, cat odour, sounds, changes in light intensity, and the passage of shadows (Osbrink and Rust, 1985b). Visual stimuli have shown to be attractive to the cat flea, but even in their absence, fleas were attracted by heat with air currents (created by a warmed moving target), as well as CO2 increased flea activity (also reported by Benton and Lee, 1965), quantifiable only in the absence of visual stimuli (Osbrink and Rust, 1985b).
Fleas possess specialised, powerful legs for jumping onto a host, and according to Osbrink and Rust (1985b) their jump seems to be directed but not precise, responding to the amount of stimulus and not to the pattern. Thirty-four centimeters have been recorded in jumping (Dryden, 1996). An increase of the size of the visual stimulus increases the response of the stimulus, thus a potential host is the more attractive to the flea the larger its size is (Osbrink and Rust, 1985b). Osbrink and Rust (1985b) could not observe any visual orientation under red light or an increase in attractiveness by increasing the complexity of patterns on the target, so that acute form vision does not occur in the cat flea (Rothschild and Clay, 1952; Osbrink and Rust, 1985b). Additional stimulation in form of air movements was necessary to evoke a directed jump onto a stationary heated target, which was simply causing attraction and orientation in the cat flea (Osbrink and Rust, 1985b).
Adult cat fleas display positive phototaxis and negative geotaxis in both the unfed and engorged state (Dryden, 1988). By that, the newly emerged cat flea residing in the carpet will move on top of the carpet canopy where it will be able to jump onto a passing host (Dryden, 1989a), enhancing the success in host acquisition (Dryden and Rust, 1994). The cat flea has proved to be most sensitive to light with wavelengths between 510 and 550 nm (green light) and insensitive to wavelengths between 650 and 700 nm (Crum et al., 1974; Pickens et al., 1987). The flea’s responsiveness to certain wavelengths of light explains observations that adult fleas congregate around vents to crawl spaces, entrances to dog houses, and window sills (Dryden and Rust, 1994). Their responsiveness to light can be used to capture fleas in light traps (Dryden and Rust, 1994).
Survival in the unfed stage
The activity of cat fleas peaks at dusk (Koehler et al., 1989; Bossard, 1997), which coincides with cat activity (Kern et al. 1992). Newly emerged, unfed cat flea can survive several days before taking a blood meal. In cool, dry air, 10% of newly emerged cat fleas survived for 20 days, while in moisture saturated air, 62% survived for 62 days (Silverman and Rust, 1985). At 24°C and 78% RH, 95% died within 15 days (Dryden, 1988), and under ambient room conditions averaging 22.5°C and 60% RH, 95% died within 12.3 days (Dryden, 1989a). No life cycle stage (egg, larva, pupa or adult) can survive for ten days at 3°C or five days at -1°C (Silverman and Rust, 1983). Survival rates of fed imagines without any given environmental conditions were stated as 234 days (Bacot, 1914), 58 days (Soulsby, 1968) and 11.8 days (Osbrink and Rust, 1984). At temperatures of 5-15°C and 70-90% RH C. canis imagines were observed to survive seven days and C. felis adults an average of ten days. Derived from investigations with different environmental conditions, the survival time of unfed adult fleas increases with increasing humidity and sinking temperature and varies between 0.5 days at 35°C/2% RH and 40 days at 16°C/100% RH (Silverman et al., 1981). Longevity of unfed adult cat fleas increases significantly in saturated air at 16°C compared to combinations of lower RH’s and higher temperatures (Silverman et al., 1981) (see Table 1).
Table 1: Effect of temperature and humidity on the longevity of unfed adult female cat fleas (Ctenocephalides felis) (average number of days for 90% mortality)
% relative humidity
For C. canis, adults were maintained at 8-10°C in saturated air for up to 58 days (Bacot, 1914). Low RH, associated with subfreezing temperatures, is likely to preclude adult cat flea survival off the host (Silverman et al., 1981). During the warmer months of the year, it is doubtful that adult fleas can live for more than a week in the absence of a host or a suitable microclimate that is relatively cool and moist (Silverman et al., 1981).
Reproduction as main adult function
Once on a host, the cat flea begins feeding within seconds and mating occurs on the host in the first eight to 24 hours, with most females having mated by 34 hours (Akin, 1984; Dryden, 1990) (see also Egg). Female cat fleas seem to have multiple matings, for young as well as fully mature and gravid females have been observed in the act of mating (Akin, 1984). Furthermore it has been observed that the spermatheca (sperm holding organ) acquires progressively more sperm over the first 24 hours (Akin, 1984). Multiple mating of one female with several males and sperm precedence which means that sperm deposited by the last male is the first used for fertilisation, is often combined with protogony (i.e. females tend to develop before males) in insect species (Thornhill and Alcock, 1983). Although most insect species exhibit protandry (males tend to emerge before females), cat fleas belong to a much smaller group that exhibits protogony (Thornhill and Alcock, 1983). The multiple mating (Akin, 1984) and the protogony may speak for possible sperm precedence in cat fleas (Dryden and Smith, 1994).
After the first blood meal, the flea must continue to feed and reproduce in order to keep its metabolism in balance (Baker, 1985). The adult flea is the perfect example of a parasite that must live on its host in order to survive. As an adult, its only function is to reproduce and it must feed constantly in order to do so (Baker, 1985). According to Zakson-Aiken et al. (1996) bloodfeeding is apparently necessary for oviposition as well as for successful mating. Males require feeding before the epithelial plug is unblocked in their testes (Akin, 1984) (see also Egg and Larva).
For blood intake, the suctorial mouth parts, well adapted to piercing and sucking from the skin are used. The host’s epidermis is penetrated by the flea’s maxillae. A tube, the epipharynx, enters the capillary vessels and draws up blood while saliva from the maxillae is deposited in the surrounding tissue (Lavoipierre and Hamachi, 1961) (Fig. 2).
Thus minimal damage to the skin is caused (Lavoipierre and Hamachi, 1961). The saliva of the cat flea contains a substance that may soften and spread dermal tissue, assisting in the penetration of the dermis by the proboscis (Feingold and Benjamini, 1961). It further contains an anticoagulant, helping in the uptake of blood (Deoras and Prasad, 1967). The flea requires a period of between two and ten minutes to engorge (Rothschild, 1975). The amount of blood consumed by a female cat flea is an average of 13.6μl (+/-2.7μl) per day, which is equivalent to 15.15-times the body weight (Dryden and Gaafar, 1991). Female fleas increase their body weight by 40% during a one hour stay on a host while male fleas only show an addition of 3%. Within 48 hours the fleas reach their maximum weight. In females an addition of 140% (here 1.08 mg) respectively in males of 19% (here 0.43 mg) could be recorded (Schelhaas and Larson, 1989).
Male fleas feed less frequently than females. Females were observed attached and feeding in one site for more than three hours, whereas males were rarely attached for periods longer than 10 to 20 minutes as reported for the bird flea (Ceratophyllus idius) (Schelhaas and Larson, 1989). Unpublished laboratory observations by Pospischil (2001, personal communication) stated the maximum time of feeding of C. felis to be 5-10 minutes and of Archaeopsylla erinacei, the hedgehog flea, 20 minutes. Males do not only feed less than females, they are also more active on the host (Dryden, 1990).
Once cat fleas feed on a host for a few days and initiate reproduction, they apparently reach a point at which they become dependent on a constant source of blood (Dryden, 1993). By now the cat flea is thought to be a permanent parasite of its host. Dryden (1989b) found 85% of female and 58% of male cat fleas to be still present after 50 days on cats which have been restricted in their normal grooming activity (by declawing, fitting with an Elizabethan collar and housing in specially designed metabolic cages).
Others report only a recovery of 22% of the fleas after 22 days on a cat (Hudson and Prince, 1958). A permanent association of the cat flea with its host has already been described by Elbel (1951) and Deoras and Prasad (1967). Fleas leaving the host will either be dead or will die within four days (Dryden 1989a). Cat fleas which have fed for five days on a host and then been removed and held at approximately 24°C and 78% RH, died within 48 hours (males) respectively 96 hours (females) (Dryden, 1988). When fed only for twelve hours and then removed from the host, 5% were still alive at 14 days (Dryden, 1993) so once a few days are spent on a host, a permanent and vital relationship seems to be established.
Maximum longevity of cat fleas has not completely been demonstrated, but survival on hosts which have been restricted in grooming activity has been reported for at least 133 days (58% of all the female fleas were recovered) (Dryden, 1989b). Cat fleas housed in screen-covered microcells were reported to have an average on-host longevity of 7.2 days for males and 11.2 days for females (Osbrink and Rust, 1984). C. canis has been reported to live for up to two years when fed on dogs (Harwood and James, 1979).
An important role in the survival and longevity of fleas on the host is played by the grooming behaviour of flea-infested animals (Hudson and Prince, 1958; Osbrink and Rust, 1984; Wade and Georgi, 1988). Cats spend a considerable part of each day grooming themselves and have been shown to remove up to 50% of their flea parasite load within one week (Wade and Georgi, 1988). Some pets may tolerate a small to moderate number of fleas, others groom themselves almost constantly, thereby ingesting and dislodging many of the fleas (Dryden, 1993). Osbrink and Rust (1985a) reported of 70% of feline hosts having only relatively few (<7) fleas. Any cat flea dislodged from the host through grooming activity must return to the host or acquire another within a couple of days or the flea will die (Dryden, 1993).
But there is also some form of interhost movement by the adult flea (Rust, 1994), of importance also for epidemiology (see also ‘Flea Epidemiology’). Infrequent, short term contact between infested and uninfested hosts is insignificant for the movement of adult cat fleas (Blagburn and Hendrix, 1989). But nevertheless movements between hosts of 2-15% of the cat fleas infesting a host are possible (Rust, 1994).
Significantly more female cat fleas have been observed to remain on the host (Rust, 1994). Movement occurs between hosts whether the hosts are permitted to live together or not. Movement by adult cat fleas between hosts occurs at a low rate and the likelihood of establishing new infestations by adult fleas transferring from one host to another exists, but does not seem to be as important as primary larval breeding sites (Rust, 1994). Transference can also occur when cats and other hosts are killed and consumed as it is supposed for cat flea infestations of coyote, fox, and other carnivores (Rust, 1994), and known to occur in weasels (Mustela sp.) (Marshall, 1981).
Summary see Box 5.
BOX 5. Cat flea adults
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- Lavoipierre MMJ, Hamachi M; An apparatus for the observations on the feeding mechanism of the flea. Nature. 1961, 192, 998-9
- Marshall AG: The ecology of ectoparasitic insects. 1981, Academic Press, London, New York
- Osbrink WLA, Rust MK: Fecundity and longevity of the adult cat flea, Ctenocephalides felis felis (Siphonaptera: Pulicidae). J Med Entomol. 1984, 21, 727-31
- Osbrink WLA, Rust MK: Seasonal abundance of adult cat fleas, Ctenocephalides felis (Siphonaptera: Pulicidae) on domestic cats in southern California. Bull Soc Vector Ecol. 1985a, 10, 30-5
- Osbrink WLA, Rust MK: Cat flea (Siphonaptera: Pulicidae): Factors influencing hostfinding behaviour in the laboratory. Ann Entomol Soc Am. 1985b, 78, 29-34
- Pickens LG, Carroll JF, Azad AF: Electrophysiological studies of the spectral sensitivities of cat fleas, Ctenocephalides felis, and oriental rat fleas, Xenopsylla cheopsis to monochromatic light. Entomol Exp Appl. 1987, 45:193-204
- Rothschild M: Recent advances in our knowledge of the order Siphonaptera. Ann Rev Entomol. 1975, 20, 241-59
- Rothschild M, Clay T: Fleas, flukes and cuckoos. 1952, Philosophical Library, New York
- Rust MK: Interhost movement of adult cat fleas (Siphonaptera: Pulicidae). J Med Entomol. 1994, 31, 486-9
- Schelhaas DP, Larson OR: Cold hardiness and wintersurvival in the bird flea, Ceratophyllus idius. J Insect Physiol. 1989, 35, 149-53
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- Silverman J, Rust MK: Extended longevity of the pre-emerged adult cat flea (Siphonaptera: Pulicidae) and factors stimulating emergence from the pupal cocoon. Ann Entomol Soc Am. 1985, 78, 763-8
- Silverman J, Rust MK, Reierson DA: Influence of temperature and humidity on survival and development on the cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae). J Med Entomol. 1981, 18, 78-83
- Soulsby EJL (ed.): Helminths, arthropods and protozoa of domesticated animals. 1968, Baillière, Tindall and Cassell, London
- Soulsby EJL (ed.): Helminths, arthropods and protozoa of domesticated animals. 7th edn., 1982, Lea & Febiger, Philadelphia
- Thornhill R, Alcock J (eds.): Timing of mate locating. In: Thornhill R, Alcock J (eds.): The evolution of insect mating systems. 1983, Harvard University Press, Cambridge, pp 90-118
- Wade SE, Georgi JR: Survival and reproduction of artificially fed cat fleas Ctenocephalides felis (Bouché) (Siphonaptera: Pulicidae). J Med Entomol. 1988, 25, 186-90
- Zakson-Aiken M, Gregory LM, Shoop WL: Reproductive strategies of the cat flea (Siphonaptera: Pulicidae): Parthenogenesis and autogeny? J Med Entomol. 1996, 33, 395-7