Haller's organ

[4] Haller's organ is critical in both questing for hosts and mate seeing, detecting them via olfaction and the sensing of humidity, temperature, carbon dioxide, and pheromones.

[2] A 2019 study showed that the Haller's organ of Amblyomma americanum and D. variabilis uses infrared detection to sense and move towards heat within the temperature ranges of its hosts.

[5] Haller's organ is a group of chemosensitive cells concentrated on the tarsus of the forelegs, which ticks wave in front of them as with insect antennae in an alternating up and down fashion, rather than using them for walking.

[2] The morphological diversity of the sensillae within the Haller's Organ is believed to indicate that it serves several different functions, including the sensation of olfactory molecules, humidity, and temperature.

[5] Ticks in the study were most attracted to infrared wavelengths of 880 nm and were found to demonstrate thermotaxis toward the source, which importantly, was disrupted by either removing the forelegs or applying DEET to a surface.

Carr found it likely requires a quorum or minimum number of chemoreceptors to be activated in order to initiate the signal transduction cascade, and that multiple stimuli could contribute to an action potential stimulating neuronal responses.

Steullet's 1992 study showed that a source of 3-5% CO2 at up to 80 cm distance was found to strongly attract individual ticks, who may quest for potential hosts such as grazing animals from among leaf litter on the ground.

[8] Carr and Salgado, in their 2019 study on heat as an attractant for ticks via Haller's Organ, proposed that the aperture of the posterior capsule allows for directional detection of infrared radiation.