The blacklegged tick (Lyme disease tick or deer tick), Ixodes scapularis, is the smallest of the four ticks described here.  The female, the largest of the stages, is oval in shape, mahogany in color, and has long mouth parts.  The male is smaller and has shorter mouthparts (Fig. 5).  The nymph and larva are very small; the nymph is not much larger than the size of a period on this page.  Larvae of the blacklegged tick feed on mice and other small rodents, while adults prefer to feed on deer.  Nymphs will feed on almost any host, including humans.   

Adults appear in Indiana in September, seeking their preferred host, white-tailed deer.  They can be found in October and November and on warm days throughout the winter.  Adults can even be collected in April and May, but are usually not encountered during June-August.  Nymphs are active during May-July, peaking in June, and larvae can be found from July-September, peaking in August.

The blacklegged tick arrived relatively recently in Indiana, the first specimens were collected from a deer killed in Porter County in 1987.  Since then, its range has expanded considerably so that by the end of 2000, specimens had found in more than half of Indiana's 92 counties.  Established populations are more likely to be found in the northwest quadrant of the state, including Lake, Porter, Laporte, Newton, Jasper, Pulaski and Starke Counties.  It is probable that the tick has also become established as far east as St. Joseph and Marshall Counties and as far south as Tippecanoe County.  Ticks infected with Lyme disease bacteria have been collected from four counties in the northwest corner of the state:  Newton, Jasper, Pulaski and Porter Counties.  The counties with no record of blacklegged ticks are most likely to be those located on the eastern side of the state (Fig. 6).