Insects have 6 legs, a head+thorax+abdomen structure, and 0-2-4 wings, while Arachnids (Acari) have 8 legs (6 in larvae), segmented bodies with 2 parts (gnathosoma, idiosoma), and 0-2 wings
Fleas like Ctenocephalides canis and Ctenocephalides felis can cause flea allergy dermatitis and transmit diseases like Dipylidium caninum and Bartonella henselae