Great fleas have little fleas upon their backs to bite 'em,
and little fleas have lesser fleas, and so ad infinitum - Augustus De Morgan.
There can hardly be a person on the planet who wouldn't recognise a flea if they saw one; they are found literally all over the world and fossils dating back 200,000,000 years have been found in Australia.
Fleas are pesky little 'critters' that delight in hopping aboard the nearest warm blooded animal for a blood meal. All fleas (and there are over 1600 species of them) belong to the insect group Siphonaptera. Most, but not all, of these feed exclusively on one species of host. Exceptions to the rule include mouse and rat fleas which are happy to hop from one type of animal to another whenever hunger strikes.
This ability to jump species was responsible for wiping out around a third of the population of Europe in the 14th Century when rat fleas jumped off their dying hosts and transferred the bacteria responsible for the Black Death to man - it's no wonder we have an abhorrance for these insignificant looking insects.
As with probably every other living thing, even the humble flea is susceptible to parasites of its own. They can become infected with nematode worms, mites, bacterial, fungal and protozoan infections.
Impact on people
Fleas have a significant impact on humans and their pets and
domestic animals.
Flea bites directly cause:
- Itching and redness at site of bite. Scratching may lead to secondary infections and sores.
- When a flea bites it excretes chemicals in the saliva which digest and soften the skin. Allergic reaction to flea saliva is common and may result in Flea Allergy Dermatitis or FAD leading to intense, widespread itching, inflammation and hair loss.
- Severe infestations cause anemia, sometimes to the point of death, especially in vulnerable new-born animals.
Indirectly fleas bites can be extremely dangerous because they act as
vectors transmitting a number of other diseases:
Life cycle of the flea
The most easily identifiable stage of the flea's life cycle is the adult form. They have hard, shiny brown bodies, 0.1-0.8cm long, which are flattened laterally. The distinctive shape of the flea allows it to crawl unhindered through the dense hairs or feathers on the bodies of their hosts. Many species have rows of backward facing bristles, combs and spines which catch in the fur helping the flea to remain in place when the host animal tries to shake or scratch it off.
Adult fleas have specially modified mouth parts designed to feed on blood. Once they have emerged from their cocoon they can live for up to a fortnight without a blood meal, but before they emerge they can hibernate for up to one year. Blood passes quickly through their bodies and is excreted in the faeces. Flea feaces look like small black specks of dust - a surefire way to detect the presence of fleas in your pet is to sprinkle dust from their coat onto damp blotting paper. The dried blood in the faeces becomes bright red on contact with the water.
Fleas are wingless but possess an incredible ability to jump due to the
evolution of specialised back legs. The
world record for the highest flea jump (yes, there is such a thing) is 34 inches - that's a force of 200g!
Tiny white eggs, the size of salt grains, are deposited in the bedding of the host animal, or on the animal itself, at a rate of 15-50 a day. The eggs can drop off anywhere and happily mature in carpets, cracks in floorboards or in moist sand and gravel. The eggs take between 2 days and 2 weeks to hatch depending on conditions.
The larvae look like small legless caterpillars. They are blind and seek out moist dark places where they go through 2 moults before pupation; this can take from a week to several months. During this time they feed on dead skin and other organic matter, and semi-digested blood from the feaces of the adult fleas.
After the second moult the larva produces a cocoon of silk stuck together with other debris from its surroundings. During the next week to 14 days, a mature adult is formed inside the cocoon and lies dormant until conditions are right for hatching. The hibernating adult is sensitive to heat, noise, vibration and carbon dioxide, all of which indicate a nice warm body to feed off, so out it jumps ready to go on a wild feeding spree!
Eradication
- Insecticides such as pyrethrum, rotenone, and malathion eliminate adult fleas and may be dusted onto animals or used in lotions and shampoos. Chlorinated hydrocarbons and organo- phosphates are also used on suitable animals. Some of these chemicals are very toxic to certain animals and great care must be taken when prescribing and administering them. Secondary measures may be required to stop reinfection as the eggs and larvae hatch.
- Flea collars are often used for pet cats and dogs. These emit a toxic (to fleas) gas which kills adult fleas near the animal's neck. If this method of control is used, it is helpful to put a collar in the vacuum cleaner bag to kill any emerging fleas which have been 'hoovered' up. Eggs and larvae are unaffected.
- Spot-on treatments (brands include Bio-Spot, Advantage and FrontLine) provide long lasting (up to 8 weeks) effectiveness by killing adults and larvae and also prevent the eggs from hatching.
- Oral (and injectable) medications such as Program and Sentinel circulate in the blood of the host. When this is absorbed by feeding females their eggs are rendered incapable of hatching, thus breaking the life cycle.
- Careful vacuuming and frequent washing of pet bedding helps break the life cycle and reduces the size of the flea infestation.
And finally, just for fun...
A flea and a fly
Flew up in a flue.
Said the flea, "Let us fly!"
Said the fly, "Let us flee!"
So they flew through a flap in the flue.
http://www.microscopy-uk.org.uk/mag/artjun98/insecin2.html
http://www.warrenhouse.co.uk/warrenhouse/problems.htm
http://vetmedicine.about.com/library/weekly/aa042001a.htm
http://www.kcom.edu/faculty/chamberlain/arthro.htm
Nice pics of life cycle can be found at http://www.placervillevet.com/flea_life_cycle.htm