Acarina
Ticks, Mites
Animals somewhat like the spiders but having no marked division between the cephalothorax and the abdomen. Each adult has four pairs of walking legs, although an individual of the very young stages has only three pairs. The mites are generally very minute and seldom are seen by the beginning collector. They vary greatly in general appearance. Many species are extremely destructive to stored produce, to live domestic animals, and to many groups of plants. Adults of the harvest mite and early stages of the chigger mite attack man persistently.
Fig. 74.—Acarina. Dermacentor variabilis, the common dog tick of Illinois and vector of Rocky Mountain spotted fever. When engorged, the tick looks like a red berry. Actual length 0.2 inch. (Drawing from U. S. D. A.)
Ticks are larger than mites. All the species feed on warm-blooded animals, including birds and mammals. The commonest Illinois tick is Dermacentor variabilis (Say), [fig. 74], which transmits the organism causing the often fatal disease called Rocky Mountain spotted fever. Although this disease occurs only infrequently in Illinois, hikers and others exposed to ticks on excursions into the out-of-doors should carefully examine their clothing and bodies and promptly remove any ticks they find.
Diplopoda
Millipedes
Fig. 75.—Diplopoda. Parajulus impressus, a common Illinois millipede. Actual length 1.5 inches.
Fig. 76.—Chilopoda. Scutigera forceps, the house centipede, commonly found in dark basements. Actual length of body 1.0 inch.