The surviving larvae feed voraciously on adult-flea excrement and undergo at least two moltings over a course of one to two
weeks. This pre-pupal stage may be the most critical stage in regard to environmental control, which will be discussed later.
Mature larvae will actually transform into a cocoon or pupae. The cocoon is literally spun with "silk" by the mature larvae.
The cocoon is covered in this silk (that is sticky) produced by the larvae but soon becomes covered in environmental debris,
such as soil and other loose particles.
The pupal stage is the most indestructible to environmental hazards as well as insecticides. Pupae make up about 20 percent
of the total life cycle but survival can be as high as 80-90 percent, obviously much higher than eggs and larvae.
Approximately one week after the formation of the pupal stage, the newly emerged adult is ready to leap onto the host. If
environmental conditions are poor (i.e., very cold temperatures or low humidity), there may be a very long delay in the emergence
This delayed emergence is a very important detail in the flea's life cycle. Its ability to rest and emerge at a much later
date often can surprise the owner and the veterinarian. It has been proven that this delayed emergence can be up to seven
to eight months.
The triggers that allow the cocoon to hatch and promote the emergence of the adult include exhaled carbon dioxide from host.
In addition, body heat is considered to be a trigger that promotes pupal hatching.
Lastly, another trigger for hatching is vibration. As the host walks along, certain vibrations, such as debris moving about,
promote the emergence of the adult flea.
Understanding the life cycle of the flea can allow the clinician to make reasonable decisions and offer proper treatment options.
This is especially true for cases of flea-allergy dermatitis (FAD).
Canine FAD is a common disease, is often overlooked, and can range in severity. The clinical distribution can vary, but usually
it is fairly consistent in dogs and is mainly confined to the dorsal lumbar-sacral area and groin. It is characterized by
alopecia, erythema, excoriations and occasional concurrent pyoderma. Pruritus can be severe and result in substantial hair
loss, hot spots (pyotraumatic), and secondary (often recurrent) superficial pyoderma on the groin. Less common, mild pruritus
on the rump may be accompanied by more substantial, severe recurrent pyoderma of the groin.
Flea allergy in the cat can be a more challenging diagnosis. Cats are very efficient groomers and often swallow fleas, making
it very hard to convince the clinician (as well as the owner) that fleas are the cause of the pruritus. The clinical presentation
can be similar to dogs. Alopecia (caused by "over-grooming") can be present on the rump and/or groin without obvious inflammation.
Cats rarely develop pyoderma. Some cats present with military dermatitis around the neck, and it is characterized by numerous
small-crusted papules with concurrent pruritus in the same area.
Adult fleas may be seen, but are not necessary to make a tentative diagnosis of FAD. Unfortunately, atopic dermatitis uncommonly
accompanies FAD and can often confuse or distract the clinician.
In general, I recommend a good quality monthly product such as the topical spot-ons Advantage, Frontline, Vectra 3-D, Promeris
or Revolution, or the monthly oral flea product Comfortis. These products have some differences, but in general they all work
adequately for flea control. One limitation that I have noticed with some of these products is it appears they "wear off"
in about two to three weeks after application. However,I have been recently impressed with the duration of action with Vectra
3-D and Comfortis. Since some of these products may "wear off" in about two to three weeks, active adult fleas may be noticed
just before the next dosage. This is not due to resistance, but to the limitations inherent to these products. Sometimes,
frequent swimming or bathing (especially with harsh shampoos) can remove some of these products as well. Capstar is recommended
and can be used in acute infestations for a rapid onset in flea control. It can be used as a long-term maintenance regimen
every other day or every third day.