Spiders are arthropods. They have eight legs and chelicerae with fangs that inject venom. They are the largest group of arachnids and rank seventh in total species diversity among all other organisms.
Cockroaches are insects of the order Blattaria or Blattodea, of which about 30 species out of 4,500 are found in human habitats. About 4 species are common pests.
The mosquito belongs to the family called the Culicidae. Mosquitoes are considered a nuisance because they consume blood from living vertebrates, including humans. Some mosquitoes spread diseases such as Malaria.
Ants are social insects. They belong to the Formicidae group. Ants are related to wasps and bees, which belongs to the order Hymenoptera.
Fleas are insects from the Siphonaptera family. They are wingless, with mouthparts adapted for piercing skin and sucking blood. Fleas are parasites. They feed by practicing hematophagy. (Feeding off the blood of mammals/birds).
Rats are medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus Rattus, the most common to humans are the black rat, Rattus rattus, and the brown rat, Rattus norvegicus.