Of more than 1200 described species of trombiculid mite, only about 50 are known to attack humans or livestock. Only the larvae, popularly known as chiggers, are parasitic on vertebrates. They are widely distributed and in many countries, cause a dermatitis in humans, although not all chiggers cause an itchy reaction.
Trombiculid larvae (Figures IV.4, IV.5) normally parasitize rodents and birds but, given the opportunity, will feed readily on humans. The non-parasitic female lays eggs in damp but well drained soil. Typical breeding places are cultivated alluvial river banks in Japan, scrub jungle, grassy fields or untended gardens with a rank growth of grass and other vegetation.Figure not available in preview mode
Figure not available in preview mode
Life cycle (Figure IV.6)
On hatching, the six-legged larvae, which are creamy-white to bright red in colour and 0.25 mm long, ascend grass stems or the tips of fallen leaves and wait in clusters until carbon dioxide from a passing host activates them. The round or oval-shaped larvae have a …