You wouldn’t normally think of earwigs being parasitic, but some tropical forms of them have evolved to be just that.
The Manchester Museum collection collection of Dermaptera (earwigs) contains some parasitic earwigs from the genus Arixenia. The Arixenia are unique because they are ectoparasitic. Only the genus Hemimerina shares this characteristic in the Dermapterans. The collection contains 32 specimens of the Arixenia including fluid preserved specimens collected at Gua Payau (Deer Cave) in Sarawak.
The species A. esau was first described in 1909 (See Jordan, 1909 p 313-326) from nymphal specimens found in the pouch of a naked Bulldog Bat (Cheiromeles torquatus) found by the dealers and taxidermists Gerrard & Sons. Though Jordan described the specimen, he was reluctant to state that the insect was parasitic, preferring instead to posit the theory that the insects ended up in the bat’s pouch accidentally and were actually a food source for the bat.
It wasn’t until 1957, when Lord Medway, a worker at the Sarawak Museum, was able to observe living examples of A. esau in the wild, that the theory that the species was parasitic was confirmed.
The Arixenia esau were observed swarming on the bats themselves and the floors of caves, where they fed on guano, insect remains and even parasitized a Tenebrionid beetle with their heads under the elytrae, feeding on it while it still lived. (Medway 1958) Their feeding habits were described by Medway:
Insects from the [cave] floor behave in the same way on a human hand. Clinging with their sharp cruved claws, hard to shake off, they move jerkily around with near hysterical agitation; it is a very ticklish feeling. All ignored the skin on my palms, some found my metal watch strap an impassible barrier, and several began to feed on the soft sweaty skin between and on the back of my fingers. In feeding they pressed their mandibles to the skin, and, opening and closing them rapidly and continously, scraped the skin surface and moved steadily forward. The direction of the movement was always upwards, and changed at once if the hand was turned. The sensation was not painful, but was very irritating-like the gentle beginning of a subtle torture-and since each “bite” was applied to a fresh place, would never break the skin, but would clearly scrape the surface clean.
Hmmm, yet somehow I don’t think this is going to take off like those fish pedicures.
ON THE HABIT OF ARIXENIA ESAU JORDAN (DERMAPTERA), Medway 1958: Proceedings of the Royal Entomological Society of London. Series A, General Entomology Volume 33, Issue 10-12