Order Siphonaptera (Fleas)

Fleas: Adult and immature cat flea. Modified from Folsom 1913.

Introduction

Fleas are small (2 – 10 mm), wingless insects that are laterally compressed (sides pushed together), and ectoparasitic on mammals and birds. Adults of all known species are blood feeders and have a unique arrangement of mouthparts to achieve this end. Some fleas are champion jumpers, while others move about by walking. Fleas have complete metamorphosis. Immature fleas are pale and worm-like with a hardened head capsule and are sparsely covered in long hairs. Immatures are free living and eat organic material. The pupa is covered in a cocoon that is coated in debris.

Several species of fleas may be found on dogs and cats. The most common of these are the cat flea, Ctenocephalides felis (Bouché), dog flea, Ctenocephalides canis (Curtis), human flea, Pulex irritans (Linnaeus), and poultry sticktight flea, Echidophaga gallinacea (Westwood). However, the cat flea is the most common flea infesting dogs and cats in the United States.

Life Cycle

Fleas are Holometabolous, their life cycle consists of four phases: egg, multiple instars, pupa, and adult. "Complete metamorphosis" is the common term for this life cycle. Insect orders with this life cycle are grouped under the term Endopterygota because immatures never have visible wing buds. The pupal stage is only found in the Endopterygota. This is typically a resting stage (e.g., the chrysalis of butterflies) where the insect undergoes a final metamorphosis from immature to adult.

Immature fleas look very different from adults. They are white, slender, have few short hairs, and are about 2.5 mm (1/10 in) in length (see figure, right).

Collection and Preservation

Fleas are small and fast. If you suspect you have found fleas but can't confirm it, they can be easily collected by placing a pan of slightly soapy water in the infested area with a small light over it (e.g., a small desk lamp) switched on at night to attract them. Special combs are available at pet stores that are effective in recovering fleas from the fur of household pets. Flea specimens collected for identification should be preserved in alcohol.

Types of Fleas

Cat Fleas (Ctenocephalides felis)

The eggs of cat fleas are white, smooth ovals with rounded ends, measuring 0.5 mm (1/50 in) long. The eggs are laid by the female fleas while on the host, and the eggs are scattered by the host. Larvae hatch from eggs in 1 to 10 days.

The larvae of cat fleas when first hatched are white, slender, have few short hairs, and are about 2.5 mm (1/10 in) in length. They feed on organic debris and the feces of adult fleas. After feeding flea larvae darken. Larvae undergo three instars during their development, and the third instar is about 5 mm (1/5 in) in length. Larvae develop in 5 to 11 days, but may take up to 21 days if conditions are not favorable. Flea larvae can be killed by desiccation and excess heat, and are therefore unlikely to develop in outdoor areas without shade. They often burrow to avoid sunlight.

Larvae of cat fleas spin cocoons prior to pupation. If the larva is disturbed shortly after spinning the cocoon it will emerge from the cocoon. Some of these larvae will spin another cocoon, while others will become naked pupae. Vacuuming may cause larvae that have recently spun a cocoon to emerge from the cocoon. Interestingly, naked pupae are more tolerant of insecticides that pupae in cocoons.

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Superorder	Holometabola
Order	Siphonaptera
Superfamily	Pulicoidea
Family	Pulicidae
Subfamily	Pulicinae
Tribe	Archaeopsyllini
Genus	Ctenocephalides

Scientific Name

Ctenocephalides felis

Common Name

cat flea

Adult cat fleas can emerge from pupae as soon as 5 days after pupation. However, the adult will often remain in the cocoon waiting for a trigger such as physical pressure, heat, and/or carbon dioxide. When the right conditions occur the adult will emerge from the cocoon. Adults may remain in the cocoon for 140 days. Occupants of dwellings my experience plagues of adult fleas after returning from lengthy absences. The return of humans and pets provides the necessary stimulus for mass emergence of adults that have been waiting patiently.

The cat flea life cycle may be completed in 12 to 174 days. However, the development of cat fleas in a house usually takes from 3 to 5 weeks.

After emergence from the cocoon, adult cat fleas immediately seek a host. They are attracted to heat, carbon dioxide, and movement. Additionally, they are attracted to sunlight and move up. Female cat fleas begin laying eggs within 36 to 48 hours after feeding and may produce eggs for more than 100 days. They may lay 1300+ eggs in the first 50 days they are on the host.

Common Fleas

The cat and dog flea look very similar. The dog flea has two notches and spines on the hind tibia. The human flea does not have the genal and pronotal combs that the cat and dog fleas have. The poultry sticktight flea does not have combs and has 18 to 20 small cone shaped bristles on each hind coxa.

Medical Issues Associated with Fleas

Both the dog and cat fleas will attack humans and pets, and can be intermediate hosts of the dog tapeworm. The Oriental rat flea (Xenopsylla cheopis (Rothschild)) found on imported black and Norway rats was instrumental in spreading bubonic plague long ago, but is less important today. Another disease transmitted by the oriental rat flea is murine typhus. It is transmitted to humans by rubbing feces or crushed bodies of fleas in open wounds. Murine typhus infects humans and small mammals and may also be transmitted by the cat flea.

Summary and Resources

Eight families and ~314 species of Siphonaptera are recorded from North America North of Mexico. Mallis (1997) and Triplehorn and Johnson (2005) are good general references for information about this order.

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Print References

First Detector Entomology Training Project