Limit of Heat: Heaven and earth turn strict

February 29th, 2012
by Jo Law

The second month of the new year in the Gregorian calendar is drawing to an end. Soon, by the meteorological reckoning of the seasons adopted in Australia, Autumn begins. I wonder whether this current solar term does truely turn out to be the limit of heat. Certainly, if we go by the long-term averages in Bellambi and Wollongong, it will not be the limit of wetness here, where February and March receive the highest rainfall. The Bureau of Meteorology also predicts a wetter Autumn for south-eastern Australia although computer modelling is showing that the dominant La Niña pattern will continue to weaken. Grain farmers in southern New South Wales are not in favour of the prospect of having a wet Autumn; while our concerns are of a different nature.

The warm temperatures, high humidity, and high rainfall in combination with the rampant growth of grass in our backyard are providing the ideal condition for ticks to hatch. The paralysis ticks (Ixodes Holocyclus) of eastern Australia is of the three-stage ixodid variety. While undergoing development as larval, nymphal, and adult, these ticks attach themselves to a new host animal at each stage for hematophagic feeding (that is on blood). Unsuspecting large animals, such as ourselves, wander through the long grass unaware that a larval tick, hydrated by the ample moisture, is questing on the end of the long green blade. The Haller’s organs on ends of its first pair of legs detect the surrounding humidity, temperature and carbon dioxide level via the sense of smell. As these data signals approach of a host, the creature seizes the opportunity and latches on. When it is satisfied with having found a warm, secure position on the body,  it inserts its hypostome into the host’s skin, injects toxins, and feeds.

Surprisingly the life cycle of a tick can take up to a year. On the warm moist coast of the eastern Australia, they can be found at any time of the year, although adult females commonly lay their eggs as summer approaches. Larvae, therefore, are aplenty at this time of the year, particularly when the conditions are as favourable as they have been. So the only recourse for us is to mow the lawn, once again tidy up the backyard, and take back the garden.

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