What attracts fleas?

Summary

During host-finding, cat fleas are primarily attracted to visual and thermal stimuli (light and heat). Other cues, such as carbon dioxide and air movement, help reinforce the detection of a suitable host.

Attraction Factors:

Light Movement Air Currents Host Odor Gravity Warmth Physical Contact Carbon Dioxide Time of Day Flea Age Flea Gender Host Color Host Size

Details

Upon emerging from their cocoon, adult fleas immediately seek a blood meal. They must feed within a week to prevent starvation. Cat fleas find hosts primarily through visual and thermal cues. However, a combination of multiple stimuli reinforce the accuracy of host detection and elicit the best jump response.

Light (Phototaxis)

Adult cat fleas are attracted to sources of light. When placed in a dark area, 93% of the fleas will move to a lighted area within 40 minutes. In natural settings, newly emerged adults will climb on top of objects within the larval habitat. They then orient themselves towards a lighted area as they wait for a host.

Color of Light

Cat fleas are able to sense wavelengths between 300 and 600 nanometers (nm). They’re most attracted to wavelengths between 500 and 530 nm, which is a green-yellow colored light Fig 1. Green-yellow light attracts over twice as many fleas as standard light. Outfitting lighted flea traps with a green-yellow filter significantly improves their performance.

Other colors of light aren’t nearly as attractive. Blue and green filters produce similar results to standard light. Filters of nearly all other colors—red, magenta, yellow, medium blue—fail to produce a better response than standard light. Cat fleas can’t see wavelengths beyond 630 nm. Thus, they’re least responsive to red light.

Intermittent Light

Attraction towards light is greatly enhanced when the light source is quickly and briefly interrupted (10 minutes on, 5 seconds off). This interruption mimics a shadow cast by a potential host as it passes. Fleas will jump in the direction of the perceived shadow.

Flea traps using intermittent light consistently attract and capture significantly more fleas than those using a constant light source. One study found intermittent light was 5-8 times more effective than continuous light. In another experiment, intermittent light traps caught 82% of released fleas, while standard light traps caught little more than 10%.

Movement

Fleas aren’t attracted to inanimate objects. In one experiment, a moving black target attracted 79.4% of fleas, but only 16.6% were attracted when it was stationary. Another experiment found that warm, stationary targets only elicited fleas to jump when additional stimuli were present, such as air currents.

Air Currents (Anemotaxis)

Air movement by itself doesn’t elicit an attraction response. A fan producing air currents at 1.6 mph doesn’t have a discernible effect on cat fleas. However, when air currents are combined with other stimuli, the attraction response is enhanced. Though there’s no relation to attraction, short bursts of air will cause fleas to jump.

Host Odor (Odortaxis)

It’s been hypothesized that fleas are most attracted to the odor of their primary host. Some species seem to respond to host odor. However, there’s no evidence that cat fleas are attracted to cat odor.

Gravity (Geotaxis)

Adult cat fleas are negatively geotactic (or gravitactic), which means they move away from gravity. Newly emerged adults climb atop small nearby objects. There, they wait for an animal to pass by. In homes, adult fleas move to the tips of carpet fibers. Outdoors, they’ll climb to the top of ground vegetation.

Warmth (Thermotaxis)

Activity

Cat flea activity dramatically increases in response to heat (positively thermotactic). Fleas wildly jump around in random directions when a warm object is placed directly in their environment.

Attraction

Fleas are attracted to warmth, because it signifies the body heat of a potential host. They’re most attracted to targets with temperatures of 104°F (40°C) Fig 2. However, there’s still a high level of attraction at 122°F (50°C), which shows that fleas don’t discriminate between hosts. This refutes the notion that fleas are attracted to the specific body temperature of their preferred host.

Heat alone isn’t enough to attract fleas. They’ll orient themselves towards a heated object, and even wobble back and forth to increase depth perception. However, they won’t jump unless further stimuli are present, such as air movement. Flea traps using heat as the sole attraction stimulus don’t work. Similarly, adding heat to a lighted flea trap doesn’t improve results. Overall, thermal cues plays a minor role in host-finding.

Host Abandonment

Fleas won’t abandon their host unless it’s dying and growing cold. The fleas will then jump to the nearest warm animal. In a natural setting, this can occur when dogs or cats attack and kill smaller prey animals.

Cocoon Emergence

Heat, along with pressure, triggers pre-emerged adults to exit their cocoons. These two cues signify that an animal is likely to be resting on top of the cocoon. Warm human breath is enough to stimulate emergence. Without heat or pressure, cocooned fleas can remain quiescent (dormant) for up to five months.

Physical Contact (Thigmotaxis)

As just mentioned, physical pressure is a main trigger which causes pre-emerged adults to emerge from their cocoons.

Carbon Dioxide

Activity

Cat fleas respond to increases in carbon dioxide. When CO2 is introduced to a jar of fleas, they’ll frantically leap around. Carbon dioxide from human breath elicits a greater reaction than gas from dry ice, indicating that warmth and humidity increase the attraction response. Another study also saw increases in jumping and activity when exposed to short bursts of CO2. One study found that CO2 only increased flea activity when visual stimuli were absent.

Attraction

In a related species, the dog flea (C. canis), CO2 was seen to cause attraction. It’s believed to be the initial cue which brings the fleas near to the host.

Time of Day

Fleas are most active a few hours before sunset. Their activity remains high throughout the night, as evidenced by studies done with lighted flea traps. Flea host-finding appears to be synchronized with the resting times of domestic pets.

Flea Age

Older fleas are more responsive to attraction cues than younger adults. Fleas that are 5-6 days old are most responsive Fig 3. Similarly, 1-3 day old fleas are more responsive to lighted flea traps than those less than a day old. Young fleas are less responsive because, after exiting their cocoons, there’s believed to be a brief period of final maturing before host-finding is initiated.

Flea Gender

There aren’t any known differences between the responsiveness of male and female cat fleas.

Host Color

In one study, cat flea attraction was tested with the colors red, blue, black, yellow and white. Red and blue were the most attractive, with white being the least attractive Fig 4. White has continually shown to be the least attractive color to cat fleas. In one experiment, 78% more fleas preferred red to white. Their response to the white target increased as the surface area of red increased.

Host Size

Cat fleas aren’t attracted to small targets. In a natural setting, small targets would likely be unsuitable hosts, such as rodents. One experiment used targets with diameters of 8, 13, and 20 centimeters, and the responsiveness of fleas was 21.2%, 42.5%, and 43.6%, respectively.

References