Fleas have a four-stage life cycle consisting of egg, larvae, pupa and adult. Identifying fleas at all stages of the life cycle is important in fighting an infestation. While adult fleas are rather easily killed or driven from a host by using insecticides, flea pupa are highly resistant to insecticide.
Flea cocoons are about 5 millimetres long and ovoid in shape. The cocoon is made of a sticky silk, which picks up material from the environment. Thus, the appearance of a flea cocoon depends on the environment in which it is found. A cocoon found in dirt will be brown or black in colour. A cocoon found in carpet will be the colour of the carpet fibres. The pupa, covered in material from the environment, will be effectively camouflaged and difficult to pick out by merely looking.
The flea cocoon, encased in its thick silk and encrusted with whatever sticks to it, is not only difficult to see, but also highly resistant to pesticides and changes in temperature and humidity. A pupa may hatch in as little as a week, or if there is no food source, it may remain dormant for as long as a year, surviving freezing temperatures through the winter.
A flea pupa, although protected from pesticides and the weather, is nonetheless highly sensitive to some subtle changes in the environment surrounding it. A pupa can detect an increase in carbon dioxide or in temperature and can feel slight vibrations in the ground and air. When a pupa detects these changes it knows a host is nearby, and the adult will emerge and feed almost immediately.
Where to Find Flea Cocoons
Unlike the larval and adult stages of the flea's life-cycle the pupa does not remain attached to a host. The larva will drop off the host animal to pupate in the host animal's environment. Flea pupa can be found indoors in carpets where they nestle in the pile, or outdoors in vegetation or bare soil.
Controlling Fleas in the Pupa Stage
While they may be terribly difficult to see and to kill, fleas in the pupa stage can be removed from interior spaces with a powerful vacuum cleaner. Vacuum all furniture and carpets, especially in areas your pets frequent. Flea pupa in outdoor environments may be minimised by eliminating the small rodents on which flea larva often feed.