Insect Ectoparasites

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Cat flea

Bird louse

Pig louse

Wallaby fly

Bat fly

Bee louse

Insect ectoparasites are those insects that live on the outside of other animals (ecto = outside). Most of these insects survive off the blood of their hosts, although some also eat skin, hair and other secretions. To qualify as a true ectoparasite you must have an intimate relationship with your host. For example, mosquitoes are not ectoparasites; they do not live on humans, but only visit for a blood meal. Insect ectoparasites are often highly adapted to their specialised host environments. Typical adaptations include loss of functional wings, flattening of the body, strong legs and claws for clinging onto the host, and biting or sucking mouthparts for taking blood meals.

Fleas

Fleas (Order Siphonaptera) are an entire order of insects that has specialised in sucking the blood of mammals and birds. There are over 2,380 described species in the world, with at least 89 described species known from Australia. They are holometabolous (complete metamorphosis), with the flattened wingless adults spending almost all their time on the host feeding on blood. The worm-like larvae live separate from the host in nests, under floors, and in sand where they feed on debris, such as the faeces produced by the host animal.

Unlike lice there are no fleas found on truly aquatic hosts such as seals. Australia has many species which have specialised to live on marsupials and on native rodents.

Fleas have been important in human history. Fleas can act as vectors by transmitting micro-organisms from host to host. An example of this was the transmission of bubonic plague between rats and humans. This disease was responsible for the Black Death of the Middle Ages. This major outbreak occurred about 680 years ago in Europe and Asia, killing off up to one third of the human population, and leading to many significant social changes. Fleas are also important vectors of the rabbit biological control agent myxomatosis in Australia.

Lice

Lice (Order Phthiraptera) are even more specialised, and spend their entire life cycles on their hosts, which are birds and mammals. Lice are hemimetabolous (incomplete metamorphosis), and feed on hair, skin, secretions, and in some species, blood. Eggs are laid on the host, and the immature lice also live on the host.

The specialisation of lice extends to where they live on the host. For example, there are three lice which occur on human hosts, and each has its own area of specialisation. The crab or pubic louse Pthirus pubis infests the pubic regions, the head louse Pediculus humanus capitis prefers the head, and the body louse Pediculus humanus humanus infests clothing on the body of the host human. There are species of lice that occur on aquatic hosts such as seals, with one species even living on the inner lining of pelican beaks.

Lice act as vectors of microbial diseases in certain conditions, the most serious of which is rickettsial typhus.

Other ectoparasites

Ectoparasites also occur as specialised groups within the Order Diptera (Two-winged Flies). These include the sheep ked Melophagus ovinus and relatives (Family Hippoboscidae, Order Diptera). There are also several other families of Diptera, such as the spider-like Nycteribiidae and the Streblidae which live on bats.

Other insects and spiders can also be hosts for ectoparasites. The bee louse Braula coeca (Order Diptera) occurs on honey bees, and has been introduced into Tasmania. Some species in the beetle family Rhipiphoridae (Order Coleoptera) have larvae which are ectoparasites of other beetle larvae. Some larval wasps (Order Hymenoptera) are ectoparasites on spiders, although most wasp larvae are endoparasites (endo = inside) living inside the body of their host.

Insect Ectoparasites

Fleas

Lice

Other ectoparasites

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