Making Sense of Rodent Senses

By Dr. Stuart Mitchell

Making sense of a rodent infestation requires a sense of a rodent species' senses. A sense of a rodent species' senses requires making sense of the stimuli rodents can sense.

Sense of vision

The cornea and other eyes structures bend light rays to focus on the retina. The image is formed upside down and is inverted by the brain. The retina (like film in a camera) is where visual images are formed, sensed, and converted into nerve impulses that are processed in the brain. The optic nerve is located in the back of the retina and transmits impulses from rods and cones to the brain. This allows the animal to mentally process what is being seen. Although relatively reduced vision, rodents' eyes are positioned closer to the sides of the head, providing a wider field of vision to avoid predators.

Sense of hearing

Vibrations in the air are converted into nerve impulses that are interpreted by the brain as sound. The external ear (pinna and ear canal) funnels sound wave vibrations into the ear and toward the eardrum. The middle ear amplifies and transmits vibrations from the eardrum to the inner ear. The inner ear has sensory receptors to convert mechanical vibrations to nerve impulses. The pinna is the visible part of the ear and made of cartilage covered with skin. Rodents can move the pinna for directional hearing.

Sense of smell

A chemical sense similar to taste, receptor cells are within the mucous membranes of the nasal cavity. Odor molecules dissolve in the mucus and come in contact with receptors. Cells transmit impulses to the olfactory bulb, which sends impulses to the brain and is interpreted as smell.

Sense of touch

Skin contains sensory neurons that can detect chemical, mechanical, and thermal stimulations related to pressure and temperature. Sensations are soft contact, deep pressure, vibration, hair movement, heat, cold, and pain. Nerve endings protect against injury or damage.

Rodents make sense of their environment with keen senses. Keen senses result in tropism or turning toward or away from a stimulus. The word tropism comes from the Greek, tropos, "to turn." Positive tropism means to turn toward the stimulus while negative tropism means to turn away from the stimulus.

There are three main types of tropism.

1. Geotropism—turning toward (positive) or away (negative) from the ground or earth.
2. Phototropism—turning toward (positive) or away (negative) from light.
3. Thigmotropism—turning toward (positive) or away (negative) from touch or contact.

Rodents are quite inquisitive, social animals. Novel situations interest them. Making sense of both rodents' senses and the use their senses in reaction to stimuli within their environment allows for optimal management strategies.

Making sense of senses better enables pest management professionals to see the "LITE."

• L – Locate rodents based upon behavior
• I – Identify the rodent down to species
• T – Treat rodent infestations based upon biology and behavior
• E – Exclude rodents to prevent re-infestations