194 MITES AND TICKS 



infrequently mites are of ecological importance in controlling the 

 numbers of insects, spiders and other mites by eating their eggs. 



Enemies 



The predators of mites include a large number of arthropods, 

 including other mites, insects, spiders and so on, some of which 

 appear to specialise in an acarine diet. Thus species of Coniop- 

 terygidae (Neuroptera) appear to prey on the fruit-tree red-spider 

 mite Metatetranychus ulmi both in the larval and adult stages. The 

 larvae pierce the mites with their jaws and suck out the contents, 

 leaving dry empty skins. The mite eggs are also sucked dry, their 

 completely empty shells alone remaining. The adult insects pick 

 up mites and devour them, bite off the top halves of the eggs and 

 remove the contents. When hunting for food they move quickly 

 and at random over a leaf, feeling the surface with their palps. 



On the whole, despite this, mites tend to be avoided by many 

 predators and their brilliant colours may well be a form of warning 

 coloration. It is rare for spiders to kill or eat mites. According to 

 Bristowe (1941)* this is in part due to their strong chitinous exo- 

 skeletons, but in the main to distastefulness. The Oribatei come 

 into the former category. They move very slowly and draw in their 

 legs at the first alarm. In this way they escape the attention of many 

 spiders and most of those that do attack them find it impossible to 

 pierce their strong armour. Of the remainder the majority are dis- 

 tasteful. Often they are rejected after one touch and a spider which 

 bites a mite will not infrequently retire to wipe its mouth on the 

 ground. Some species of Holothyrus produce a secretion which is 

 poisonous to poultry. 



The edibility of water mites has been investigated by Elton 

 (1922) and Cloudsley-Thompson (1947) who have concluded that 

 the bright colours of so many species may have a sematic function 

 and be correlated with unpalatability if not distastefulness to pre- 

 dators. It is quite probable that the fact that so many species are 

 bright red in colour and conspicuous against green vegetation, as 

 the berries on holly, may be the result of Miillerian mimicry — the 

 species tending to resemble one another so that numerical losses 

 involved in teaching would-be predators to avoid them are re- 

 duced. The common colour facilitates the immediate recognition 



