THE RED BEAST OF COPELAND

Ian Humphreys

For several years now, regular visitors to the Observatory have been aware of what were commonly termed 'bracken mites'. They were known to cause severe itching once attached to their human host. In fact, these creatures are known around the world and, relative to their size, they probably cause more torment than any other creature on earth. The creature has recently been identified as a Trombiculid mite, commonly known as the chigger, scrub mite, harvest mite, redbug, kedani mite or (as in the title) bête rouge. In certain areas around the world some of the 10,000 or so species are thought to transmit serious diseases such as scrub typhus and epidemic haemorrhagic fever. Happily, this is not likely to be the case with the Copeland version of the 'red beast', Trombicula (Neotrombicula) autumnalis.

Morphology

In fact, the common names apply only to the six-legged larval stages of the mites (Acarina) belonging to the family Trombiculidae. These larvae are incredibly small; barely visible to the naked eye at just 0.2 mm in length. They appear red to orange in colour, are rounded, with four simple eyes and breath through their cuticle. They are also the only ectoparasitic stage in the mites' life cycle.

The eight-legged adults and nymphs are velvety, scarlet mites that are free living, probably feeding on arthropod eggs or minute insect larvae. They have a pronounced figure of eight shape and are much larger than the larvae at a full 1 mm long.

Life Cycle

Much of the surface of our Island suits the preference of female adult mites for laying their spherical eggs, singly or in small groups, in damp, but well-drained soil. The six-legged larvae eclose (hatch) from their egg after about one week, eventually climbing up whatever vegetation is encountered (such as bracken). They then await a host. Trombicula mites are not particular about who or what they feed on, attaching to a wide range of arthropods, reptiles, mammals and ground nesting birds. Clothing offers little protection against such a small parasite, although they do tend to congregate where clothing obstructions are encountered.

Once on the host's skin, the larva attaches itself using its blade-like chelicerae. It then injects a fluid which digests tissue, often causing dermatitis and intense itching. Scratching may then lead to secondary infections. Surrounding tissues harden, forming something akin to a drinking straw. After feeding on lymph fluid (not blood) for a few days the larva drops to the ground becoming quiescent for several days as a nymphochrysalis, before shedding its skin, or moulting, to become an active nymph. After feeding, the mite enters a further inactive stage as an imagochrysalis from which an adult emerges. The nymph and adult are not parasitic, being mobile predators and feeding on arthropod eggs and larvae.

Preventative action

It would, perhaps, be possible to eliminate mites from the island either by removing their habitat using herbicides or killing the mites themselves using appropriate insecticides. However, both of these options would drastically alter the ecology of the Island and would also require the transport, storage and use of hazardous chemicals. Neither option is acceptable on the Observatory.

The elimination of tall vegetation in areas frequented by visitors would greatly reduce the numbers of mites attaching to human hosts. This could be achieved through regular cutting of wide pathways, to encourage growth of grass instead of bracken.

There are a number of precautions which visitors can take to avoid the mites.

1. Avoid walking through tall vegetation when mite larvae are present. Keep to the mown pathways and areas of naturally occurring low growth. Try to avoid brushing against tall vegetation such as bracken.
2. Wear long Wellington boots, treated, if possible, with repellent.
3. Limit the time spent standing still among long vegetation, thus reducing the opportunities for attachment of parasites.
4. Use contact repellents such as di-methyl phthalate, DMP and di-butyl phthalate, DBP. These are available in liquid form and can be lightly smeared over clothing such as socks and trousers. They immobilize mites in a few minutes and may kill them with prolonged contact. The literature suggests that clothing impregnated with repellent is effective for a fortnight, although personal comments contradict this view, suggesting that repellent action is rapidly lost. Both DMP and DBP have a solvent action on plastics so be cautious about what they are applied to. Benzyl benzoate is also an effective repellent.
5. If you have been parasitized, then benzyl benzoate may be used on the bites, although it should be washed off the skin after 24 hours. Anti-histamine creams will reduce the swelling and itching of bites.

Literature sources

Busvine, J.R. 1980 Insects and hygiene: the biology and control of insect pests of medical and domestic importance (3rd edition). Chapman and Hall.

Chandler, A.C. and C.P. Read 1961 Introduction to parasitology (10th edition), pp 550-554. John Wiley and Sons.

Encyclopaedia Britannica 1995 V3, p 204 and V13, pp 862-865.

Grundy, J.H. 1981 Arthropods of medical importance, pp 34-37. Noble Books.