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The head louse (Pediculus humanus capitis) is an obligate ectoparasite of humans that causes pediculosis capitis. Head lice are wingless insects spending their entire life on the human scalp and feeding exclusively on human blood. Humans are the only known hosts of this specific parasite, while chimpanzees host a closely related species, Pediculus schaeffi. Other species of lice infest most orders of mammals and all orders of birds. Like all lice, head lice differ from other hematophagic ectoparasites such as the flea in that lice spend their entire life cycle on a host.Head lice cannot fly, and their short stumpy legs render them incapable of jumping, or even walking efficiently on flat surfaces. The non-disease-carrying head louse differs from the related disease-carrying body louse (Pediculus humanus humanus) in preferring to attach eggs to scalp hair rather than to clothing. The two subspecies are morphologically almost identical but do not normally interbreed, although they will do so in laboratory conditions. From genetic studies, they are thought to have diverged as subspecies about 30,000–110,000 years ago, when many humans began to wear a significant amount of clothing. A much more distantly related species of hair-clinging louse, the pubic or crab louse (Pthirus pubis), also infests humans. It is visually different from the other two species and is much closer in appearance to the lice which infest other primates. Lice infestation of any part of the body is known as pediculosis. Head lice (especially in children) have been, and still are, subject to various eradication campaigns. Unlike body lice, head lice are not the vectors of any known diseases. Except for rare secondary infections that result from scratching at bites, head lice are harmless, and they have been regarded by some as essentially a cosmetic rather than a medical problem. It has even been suggested that head lice infestations might be beneficial in helping to foster a natural immune response against lice which helps humans in defense against the far more dangerous body louse, which is capable of transmission of dangerous diseases.
Lepisma saccharina, commonly known as a silverfish or fishmoth, is a small, wingless insect in the order Thysanura. Its common name derives from the animal's silvery light grey and blue colour, combined with the fish-like appearance of its movements, while the scientific name (L. saccharina) indicates the silverfish's diet of carbohydrates such as sugar or starches.
Tardigrades (also known as waterbears or moss piglets) are water-dwelling, segmented micro-animals, with eight legs. They were first discovered by the German pastor Johann August Ephraim Goeze in 1773. The name Tardigrada (meaning "slow stepper") was given three years later by the Italian biologist Lazzaro Spallanzani. Since 1778, over 1,150 tardigrade species have been identified. Tardigrades can survive in extreme environments. For example, they can withstand temperatures from just above absolute zero to well above the boiling point of water (100 °C), pressures about six times greater than those found in the deepest ocean trenches, ionizing radiation at doses hundreds of times higher than the lethal dose for a human, and the vacuum of outer space. They can go without food or water for more than 10 years, drying out to the point where they are 3% or less water, only to rehydrate, forage, and reproduce.They are not considered extremophilic because they are not adapted to exploit these conditions. This means that their chances of dying increase the longer they are exposed to the extreme environments, whereas true extremophiles thrive in a physically or geochemically extreme condition that would harm most other organisms. Usually, tardigrades are about 0.5 mm (0.020 in) long when they are fully grown. They are short and plump with four pairs of legs, each with four to eight claws also known as "disks". The animals are prevalent in mosses and lichens and feed on plant cells, algae, and small invertebrates. When collected, they may be viewed under a very-low-power microscope, making them accessible to students and amateur scientists. Tardigrades form the phylum Tardigrada, part of the superphylum Ecdysozoa. It is an ancient group, with fossils dating from 530 million years ago, in the Cambrian period.
Ticks are small arachnids in the order Parasitiformes. Along with mites, they constitute the subclass Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks are vectors of a number of diseases that affect both humans and other animals. Despite their poor reputation among human communities, ticks play an ecological role by ailing infirm animals and preventing overgrazing of plant resources.
The name Death's-head Hawkmoth refers to any one of the three moth species of the genus Acherontia (Acherontia atropos, Acherontia styx and Acherontia lachesis. The former species is found primarily in Europe, the latter two are Asian; most uses of the common name refer to the European species. These moths are easily distinguishable by the vaguely human skull-shaped pattern of markings on the thorax. All three species are fairly similar in size, coloration, and life cycle. These moths have several unusual features. All three species have the ability to emit a loud squeak if irritated. The sound is produced by expelling air from the pharynx, often accompanied by flashing of the brightly colored abdomen in a further attempt to deter predators. All three species are commonly observed raiding beehives of different species of honey bee for honey; A. atropos only attacks colonies of the well-known Western honey bee, Apis mellifera. They can move about in hives without being disturbed because they mimic the scent of the bees.
The house dust mite (HDM) is a cosmopolitan pyroglyphid that lives in human habitation. Dust mites feed on organic detritus, such as flakes of shed human skin, and flourish in the stable environment of dwellings. House dust mites are a common cause of asthma and allergic symptoms worldwide. The mite's gut contains potent digestive enzymes (notably proteases) that persist in their feces and are major inducers of allergic reactions such as wheezing. The mite's exoskeleton can also contribute to allergic reactions. The European house dust mite (Dermatophagoides pteronyssinus) and the American house dust mite (Dermatophagoides farinae) are two different species, but are not necessarily confined to Europe or North America; a third species Euroglyphus maynei also occurs widely. Unlike scabies mites or skin follicle mites, house dust mites do not burrow under the skin and are not parasitic. House dust mites, due to their very small size and translucent bodies, are barely visible to the unaided eye.[2] A typical house dust mite measures 0.2–0.3 millimetres (0.008–0.012 in) in length.[3] For accurate identification, one needs at least 10× magnification. The body of the house dust mite has a striated cuticle. The average life cycle for a male house dust mite is 10 to 19 days. A mated female house dust mite can last up to 70 days, laying 60 to 100 eggs in the last 5 weeks of her life. In a 10-week life span, a house dust mite will produce approximately 2,000 fecal particles and an even larger number of partially digested enzyme-covered dust particles.
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