Ectoparasites

Ectoparasites are generally arthropods that live and feed on the exterior of the host, commonly the integument. In veterinary medicine, the most common ectoparasites that infest/infect our patients are ticks, mites, lice, and fleas.  This module will guide you through the morphological characteristics that distinguish salient differences between ticks, mites, lice, and fleas as inevitably a client, family member, or member of the community will bring you a “bug in a jar” and want you to identify it. As a veterinarian, you are also on the frontlines to identify invasive or non-native parasites that have entered the country via the legal or illegal movement of animals.

General characteristics of insects and arachnids

Arachnids

This class of ectoparasites includes ticks and mites. The major identifying feature of these arthropods in comparison to insects is adult arachnids have 8 legs (4 pairs).  The arachnids (ticks and mites) undergo gradual metamorphism meaning that each stage of development can be challenging to distinguish from another as they all appear similar.  The progression of development includes eggs that are laid in the environment molt into 6 legged larvae, then molt into  8 legged nymphs, and then into 8 legged adults. Remembering that some stages of development have 6 legs is important especially with ticks since not all stages of development occur upon the same animal.

Insects

Important veterinary insects lice, fleas, and flies.  In this laboratory, we will be focusing on the salient feature of just lice and fleas. Adult insects in comparison to arachnids are adults have 6 legs (3 pairs).  Most insects (including fleas) undergo complete metamorphosis development which following hatching from an egg, the individual changes form radically between molts. In other words, unlike the mites and ticks, we can identify each separate stage of development.  Insects such as lice undergo an incomplete metamorphosis which is when individuals of different ages are of similar form but live as progressively larger instars (larval stages) between molts.  Incomplete metamorphosis is a similar process to gradual metamorphosis EXCEPT for that type of maturation occurs in ticks and mites.

Summary Table

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