Under the skin

 Eew.  “Millions of baby spiders – gross!“ is the short version of an urban myth that has done the rounds several times over. The somewhat longer version starts with a spider bite that morphs into a swelling under the skin, which erupts releasing lots and lots of tiny spiders. This story appears to have its roots in the writings of a prominent scientist who should have known better than to challenge the combined expertise of the entomological community. Spider’s eggs do not survive in live human tissues and cannot rely on this niche to assist their development into hatchlings.

Arachnotrivia: Arachnid – spider; trivia – items(pl) of relatively small concern. Spider bites can be irritating and sometimes plain dangerous if venom is released. Fortunately, in this part of the world the worst we face is a nasty bite from a redback. White-tail spider bites appear to be less serious but can cause a lot of irritation and may be the focus of a secondary bacterial infection.

Insects that pick on us. The things that can get properly under the skin are insects. It may be a little picky, but spiders (arachnids) are not insects since they lack the three-part body of a proper insect. The biting insects feed off us, rather than in us. The threats they carry are the bacteria, viruses or parasites that enter our bodies while they’re feeding. Malaria is a good example of a parasite that has adapted to biting insects that need blood to breed. Dengue and scrub typhus are further examples of this kind of complex interrelationship. Fortunately for us, the insects the really get under the skin are few and far between and these are ones that can lay their eggs in our bodies. The human warble fly , Dermatobia hominis (aka botfly) is an exotic insect from remoter parts of South and Central America that gets another insect to do its dirty work. It captures mosquitoes and lays its eggs on them in order to gets its eggs injected into  the skin of cattle and sometimes humans. These eggs hatch into larvae, which break through the skin surface. The larvae (maggots) of the common housefly are sometimes seen on human skin, for different reasons. Maggots live on dead or rotting flesh, and have been used to clean up surgical wounds. In parts of the tropics (not Australia) an interesting flea (Tunga penetrans) burrows into human skin and releases its eggs. The entry for Tunga in the current edition of the handbook of Expedition & Wilderness Medicine is suitably eloquent:

Tungosis (‘chigger’, ‘jigger’ or ‘chigoe’ flea) occurs in Latin America and Africa. After fertilisation the female flea jumps (feebly) and burrows alongside the nail fold or into the skin of the groin, loses its legs, and produces eggs each night. A painful swelling develops on the foot, typically under a toenail, and there is risk of secondary bacterial infection and ulceration.

      • ŸTreatment: the encapsulated flea must be curetted out (excised, ideally with a small surgical spoon with a sharpened edge) and iodine applied. Complete enucleation is required.
      • ŸPrevention: wear proper shoes; do not walk around bare footed.

Wurrums. The lesions of the jigger flea, Tunga penetrans are found in places like tropical South and Central America and can be a big problem for people who spend a lot of time on the beach. Another condition affecting people who lie on the sand on tropical beaches frequented (polluted) by dogs is known as cutaneous larva migrans (CLM for short). The cause is NOT an insect. It is, in fact, a type of worm that burrows along just below the skin surface, causing a highly irritating wheal wherever it goes. CLM can be treated by anti-worm medication prescribed by your doctor. As always, prevention is the best course of action – when spending time on a tropical beach use a beach towel when you lie or sit down, keep sand shoes, beach sandals or alternative foot covering on, and stay clear of places where dogs exercise.

Can’t get enough of this? More information on these and related conditions can be found at:

Micrognome, October, 2011.

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