Key to Australian Freshwater and Terrestrial Invertebrates
Phylum Arthropoda
Subphylum Hexapoda
Class Insecta
Order Siphonaptera
Common name: fleas
Overview
The Siphonaptera, or fleas, are a relatively small order of highly specialised, bloodsucking ecto- (external) parasites of mammals and birds. Adult fleas are wingless, laterally flattened, and have very small or no eyes. Their mouthparts are modified for piercing and sucking and the body is strongly sclerotised (hardened) and covered with backward pointing setae (hairs) and spines that help movement through the hair or feathers of their host. Fleas also have strong tarsal claws adapted for holding onto their hosts, long legs � the hind legs enlarged for jumping, and small antennae that tuck away into special groves on the head. Males have longer antennae and use them to grasp the female during mating. Fleas are small, ranging from 1�10 mm in length. The larvae are free-living, not parasitic, and grub- or maggot-like in appearance and typically are found in the nest, lair or bedding of their host.
Distribution and diversity
Fleas are found wherever their hosts occur. About 2,500 species are described worldwide. In Australia, species are particularly associated with marsupials and native rodents; 91 species in 34 genera and nine families have been recorded for the continent. Ten species are introduced cosmopolitan species associated with humans or domestic animals. Of the indigenous species, 72 are endemic, reflecting the endemicity of the mammals with which most species are associated.
Life cycle
Fleas mate on their host animal, and this is often triggered by warmth or a blood meal. Sperm transfer is direct. Females lay their eggs onto the animal and subsequently they are rubbed off in the nest or they are laid directly into the nest. The blind larvae hatch and feed on dead skin and other detritus from the host and other available organic material such as dead insects and vegetable matter. They develop through three instars, spin a silken cocoon and pupate in the nest of the host. The vibrations of a host often trigger the emergence of the adult flea from the pupal case, enabling it immediately to find a host and begin feeding. The complete life cycle may take from several weeks to many months, depending on the species, with adults living for many months to a year.
Feeding
Adult fleas have piercing mouthparts that allow them to feed on the blood of their host. Although many fleas are adapted to one particular animal species, some are not host specific and can feed on other animals if their preferred host is unavailable. Host ranges for individual flea species can vary from 1 to over 35 species.
Ecology
Fleas are always found close to their hosts, either in direct contact among feathers or hair, or within their nests. They are highly adaptable, and can withstand unfavourable environmental conditions, lasting days to many months without food. Some can remain in the pupal stage for up to a year waiting for a host. Fleas can occur in large numbers, and quickly move between host animals, particularly from dead hosts to seek a new one. In addition to the human flea, Pulex irritans, several other species may bite humans as well as their primary host, which is usually a domestic mammal, rodent or bird. The introduced cat flea, Ctenocephalides felis, and dog flea, C. canis, are pests of domestic pets. Some people and animals suffer allergic reactions to flea saliva, resulting in development of rashes. Infestation by fleas can also lead to hair loss as a result of frequent scratching and biting by the animal and, in extreme cases, can cause anaemia. Many flea species are significant vectors of disease, transmitting pathogens from mammalian hosts to humans. The oriental rat flea, Xenopsylla cheopis, is most frequently implicated in transmission of plague as well as well as several other human diseases. The rabbit flea, Spilopsyllus cuniculi, was used to spread myxomatosis as a biological control agent for feral rabbits in Australia.
