Re: Of what benifit are Fleas? All things have both a plus and a negative.

Annette,
	Often the key to science is approaching a question from a 
different perspective.  Many species of animals from domesticated 
cats to bandicoots to birds are parasitized by fleas specific to that 
species.  When you ask if fleas, the omnipresent pests they appear 
be, are of any benefit, we have to consider multiple perspectives. 
In addition, we have to think about the ecosystem as a connected 
whole that relies on the functions of many minute parts.
	Certainly to humans and our domestic animals, fleas appear to 
be annoyances.  Not only do fleas cause intense itching and scraggly 
coats in cats and dogs, the ingestion of fleas by these animals 
causes infestation with tapeworms which can lead to serious digestive 
trouble.  However, think about the flea from the perspective of the 
tapeworm.  Without the flea as transport, the tapeworm could not 
successfully breed and be transferred from host to host.  The 
tapeworm relies on the flea to complete its lifecycle.
	Fleas not only carry tapeworm progeny, they transmit myriad 
bacterial species including notable pathogens.  "Yersinia pestis" is 
a species of bacteria that causes the bubonic plague, also known as 
the black death.  The bacteria were spread from Asia to  
Europe in the 1300s, carried by fleas that infested stowaway rats, 
and killed nearly one third of the population.  From the perspective 
of the bacteria, fleas were instrumental in their reproductive 
success and allowed the bacteria to colonize new territory just as 
their human counterpart explorers were.  The Dark Ages were certainly 
a terrible time.  However, William H. McNeill, author of "Plagues and 
Peoples", asserts that quarantine principles, though not terribly 
effective, were first developed during the plague; we still rely on 
principles of quarantine in today's societies.
	Other pathogens that owe their success to fleas are 
"Bartonella henselae", the cause of cat scratch fever and "Rickettsia 
typhi".  Human sprawl into previously sparsely populated rural areas 
has increased the contact of domestic pets and humans with fleas of 
wild animals, increasing encounters with the bacteria.
	Fleas are proving of interest in scientific research for 
reasons other than their transmission of significant pathogens. 
Recently, a British lab showed that fleas parastizing red squirrels 
had circadian rhythms that were linked to those of their host. 
Research into circadian rhythms is an important scientific avenue for 
investigating human sleep disorders, and the flea may turn out to play 
part in the advancement of this knowledge.
	Finally, increase the perspective of the flea to encompass 
the ecosystem as a whole.  It may not appear to us that the flea and 
its pathogen and worm compatriots are beneficial to humans. 
However, each piece of the ecosystem, each niche filled, is 
significant, though the significance is not often known until the 
niche is empty.  You can imagine that somewhere there is perhaps a 
bird sitting on the back of zebra in the grasslands of Africa. 
Imagine that a significant part of its diet is fleas gleaned from the 
zebra's fur.  With no fleas, the bird soon vanishes taking with it a 
link on the food chain...
	A recent science fiction book, "Dust" by Charles Pellegrino, 
tells the story of a modern day extinction of insects and the 
subsequent crash of the ecosystem.  Though it is fiction, it presents 
interesting scenarios and food for thought.
Thanks for writing MadSci Network!
-Tinsley

References:
Circadian rhythm in fleas
  Clark F. Deadman D. Greenwood M. Larsen KS. 1997. A circadian rhythm 
of locomotor activity in newly emerged Ceratophyllus sciurorum. 
Medical & Veterinary Entomology. 11(3):213-6.

Bacteria carried by fleas
Azad AF. Radulovic S. Higgins JA. Noden BH. Troyer JM.  1997. 
Flea-borne rickettsioses: ecologic considerations. Emerging 
Infectious Diseases. 3(3):319-27.

"Yersinia pestis" Pathogenicity
Salyers, A.A. and D.D. Whitt.  "Bacterial Pathogenesis."  Washington, 
D.C.: ASM Press, pp. 218-228.