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On the Grass


Ixodes scapularis, the deer tick or black-legged tick, must feed on blood at each stage of its development. Consequently, it has a lifecycle that can last two to four years (1). Eggs hatch in the spring into a six-legged larva. After its first blood meal, the larva overwinters in leaf litter to emerge the next spring as an eight-legged nymph. The nymph takes a blood meal to develop into an adult, which waits through the winter for its final blood meal in the spring that is needed for the females to lay their eggs (2).


Ticks find their hosts using a complex sensory organ on their front legs called the Haller’s organ (3). Using this organ they sense CO2, heat, odours, and other stimuli to identify an approaching host.


Ixodes scapularis is found in the eastern US and Canada and is an important vector for several diseases of humans (2). They can survive winter conditions but are most active in the summer, with peak nymph activity preceding peak larval activity (4). The earlier activity of the nymphs is thought to aid in the transmission of human-disease causing pathogens from tick to tick (e.g. bacteria causing Lyme disease, viruses causing Powassan disease, parasites causing Babesiosis, etc.): infected nymphs feed on a host and infect it, which then infects larvae that later feed on the same host (1). Transmission to humans occurs during a tick bite.


1. 10.1093/jmedent/27.2.196

2. https://www.cdc.gov/ticks/surveillance/BlackleggedTick.html

3. 10.1371/journal.pone.0221659

4. 10.2307/3283457



Parasite Comics Team:

Dr. Chenhua Li (Lead, Ideas), Dr. Þórey Jónsdóttir (Illustrator, Ideas), Stephen Pollo (Writer, Researcher), Yuanzhe Wang (Digital Consultant).

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