Characteristics of Parasitic Insects and Arachnids

Siphonaptera (Fleas)

Fleas have three pairs of legs, a segmented body, and are 0.5 to 4 mm in size. They can jump 33 times their size. Ctenidia are hairs on their body. The female spermatheca is where the eggs are stored. They have a complete or holometabolous life cycle. The adult lays eggs, and in three weeks, the larvae emerge. In 9-15 days, the pupa stage is reached, and then the adult. Males and females feed on blood. The larvae feed on the feces of the adult fleas. The pupa is covered with earth and is motionless until the temperature changes.

• Pulex irritans (Human flea)
• Ctenocephalides canis (Dog flea)
• Ctenocephalides felis (Cat flea)
• Xenopsylla cheopis (Rat flea)
• Tunga penetrans: The female introduces itself inside the skin, producing a wound with the saliva.

Hemiptera

Hemiptera have two pairs of wings: one pair of membranous wings and another pair of hardened wings (hemelytra).

Triatoma / Chagas

They are 2-3 cm long, with a conical head and long, thin antennae. They have compound eyes and ocelli (simple eyes). They have a piercing-sucking mouth or proboscis. Both males and females are hematophagous (blood-feeding). They have a distinctive colored edge on the abdomen. Not all triatomines feed on blood. They have an incomplete life cycle: the adult lays eggs, followed by nymph stages 1, 2, 3, 4, and 5, and then the adult. Nymphs are morphologically similar to adults. They feed and defecate blood after feeding.

Blattodea (Cockroaches)

Cockroaches have a segmented body and jointed appendages. They have a chewing mouth, a dorsoventrally flattened body, and legs adapted for running. Their wings are atrophied, allowing them to glide if they fall. They have long antennae. They are mechanical vectors with an incomplete or hemimetabolous life cycle. The females carry the ootheca, where they lay eggs. Adults lay eggs, and nymphs emerge, feeding like adults. The nymph can take 1-2 years to become an adult. The adult lives 2-3 months, living in feces, sewage, and behind objects. They are mechanical vectors.

Arachnids

Mites

Mites have four pairs of legs. In cases of scabies, the male is more clinically significant than the female. The head, neck, and abdomen are not distinguishable. They have two pairs of front legs and two rear legs, with a chewing mouth (chelicerae) and pedipalps, which are sensory organs. Males have an incomplete life cycle and feet with suckers on the first two pairs and terminal suckers on the fourth pair. The third pair lacks suckers. The females have suckers on the first and second pairs of legs. The adult lays eggs, and in 3-8 days, the nymph emerges with three pairs of legs (hexapod larva). In 2-3 days, it develops the fourth pair of legs, and in 1-3 days, it becomes an adult. The nymph can produce disease.

Ticks

Ticks have four pairs of legs. Ixodidae (hard ticks) have a chitinous shield. Argasidae (soft ticks) do not. They have a hypostome with teeth or mouthparts that allow them to feed on blood. Adults and nymphs feed on blood. They have an incomplete life cycle: egg, hexapod larva with three pairs of legs, then a larva with four pairs of legs, and finally, the adult.

• Rhipicephalus sanguineus: Inflates when sucking blood. Adults and nymphs are found on a host.

Hard Ticks

Hard ticks have a dorsal shield, sexual dimorphism, are ectoparasites of reptiles and mammals, have diurnal habits, feed slowly and once per stage, and have rigid palps.

Soft Ticks

Soft ticks have no dorsal shield, no sexual dimorphism, a ventral anterior face, are ectoparasites of birds and mammals, have nocturnal habits, feed rapidly and repeatedly per stage, and have flexible palps.

Spiders

Spiders have chelicerae (chewing mouthparts), a cephalothorax, and an abdomen. Legs emerge from the carapace. They have three pairs of eyes: a single anterior pair and two posterior vertical pairs. They produce enzymes such as hyaluronidase, norepinephrine (which accelerates bodily functions), and sphingomyelin phosphodiesterase, causing cutaneous and visceral damage (necrosis in the kidney and bleeding in the liver).

Loxosceles laeta

L. laeta has sturdy legs, brisk walking, and lives alone. It has a hemimetabolous life cycle and sexual dimorphism. After fertilization, the female lays eggs in the ootheca. After embryogenesis within the egg, nymphs are released and are cannibalistic.

Latrodectus mactans

L. mactans has a large abdomen and four pairs of legs. It has a hemimetabolous life cycle and sexual dimorphism. The egg develops into a nymph, and the nymphs eat their siblings. They are diurnal. Their venom contains enzymes that affect neurons. Antitoxin should be applied within four hours. Acetylcholine, norepinephrine, and GABA are the poisons.