TABLE OF CONTENTS
Siphonaptera (Fleas): Morphology, Mouthparts, Life Cycle & Veterinary Importance
Siphonaptera is the insect order comprising fleas, which are small, wingless, laterally compressed, blood-feeding ectoparasites of mammals and birds. The name Siphonaptera reflects their specialized feeding habit—“Siphon out the Blood from the Host.” Fleas are characterized by their powerful jumping ability, piercing and sucking mouthparts, and complete metamorphosis.
This article covers their morphology, mouthparts, thorax, abdomen, life cycle, and veterinary importance.
Morphology
- Members of the order Siphonaptera are wingless insects with laterally compressed bodies and are not host-specific, infesting a wide range of hosts.
- Adult fleas are 1–6 mm long; females are larger than males, and the chitinous covering is thick and brown.
- Both sexes suck blood.
- Compound eyes are absent, and simple eyes are present.
- The antennae are short and sunk into antennal grooves or antennal sockets on the sides of the head.
- The larval forms are nonparasitic, whereas adults are parasitic.
- The third pair of legs is very well developed, allowing powerful jumping or leaping, which is supported by resilin protein in the pleural arches.
- The body is covered with backwardly directed spines. There are a large number of spines on the head and thorax, known as combs or ctenidia. Combs present on the genal area are called genal combs, and those on the pronotal area are called pronotal combs.
- Metamorphosis is complete.
- The legs are attached to the prothoracic, mesothoracic, and metathoracic regions on the ventral aspect.
Mouthparts
The mouthparts of adults are of the piercing and sucking type, whereas those of larvae are of the masticatory type and consist of triangular-shaped maxillae and a pair of powerful mandibles with serrations at the tips.
There is a pair of 4–5-segmented maxillary palps and 4–5-segmented labial palps.
Thorax
The thorax is three-segmented and has a pronotal ctenidium, two pairs of spiracles in each segment, and three pairs of legs. The third pair is long and powerful and ends in powerful claws.
Abdomen
There are 10 visible segments. The abdomen of the male flea is tilted upward in the posterior region, with a flat dorsal surface and a curved ventral surface. In the female, the abdomen is rounded posteriorly, and the dorsal and ventral surfaces are convex.
All abdominal segments have numerous backwardly directed spines. In the middle of the 7th abdominal segment, there is a comma-shaped pouch known as the “spermatheca,” which is seen in female fleas. Its purpose is to store sperm after copulation.
On the dorsal tergite of the 7th abdominal segment, there is a long, powerful bristle known as the antipygidial or antisensilial bristle. On the dorsal tergite of the 9th abdominal segment of both male and female fleas, there is a cushion-like structure with fine setae (hairs) embedded in the cushion. The entire structure is known as the “pygidium.” The purpose of the pygidium is to detect air currents around the flea.
The 10th abdominal segment is modified into the sex organs. In male fleas, the 10th abdominal segment has a pair of “L”-shaped claspers. During mating, the female will sit over the male, and the female is always larger than the male.
Life Cycle
In a day, the female flea will lay about 20 eggs, which are laid on the body of the host and in the host’s bedding material. During its lifetime, a single female will produce 400–500 eggs.
The eggs that are dropped on the body of the host will roll down and fall into the host’s bedding material. Eggs are 0.5 mm in length and appear like sugar granules to the naked eye.
The larvae develop inside the eggs, and L1 will emerge. It has 3 thoracic and 9 abdominal segments. Its anterior end has a pair of powerful teeth called “egg teeth.” At the tail end, it possesses a pair of finger-like projections known as “anal struts.” The larvae have masticatory mouthparts and feed on organic material, including blood and feces from adult fleas.
L1 molts to L2, which is longer and more elongated and lives on organic material, and then molts again to L3. Each larval stage lasts for 5 days. The L3 spins a cocoon around its body, which becomes covered with dirt and debris, and finally pupates. This stage lasts for 2 weeks or 20 days. Finally, the adult emerges.
The entire life cycle is completed in 35–40 days. The total life span is up to one year.
