What’s a pest? As define by Merriam Webster dictionary:-
an epidemic disease associated with high mortality; specifically : plague
something resembling a pest in destructiveness; especially : a plant or animal detrimental to humans or human concerns (as agriculture or livestock production)
one that pesters or annoys : nuisance
So, in our urban society, a pest is best defined as No 2 & No 3 above. To further define it, urban pests are categorised to both invertebrates and vertebrates. They are considered pests if they:-
Destructs our property or products (i.e. termites, rats, beetles)
Spread diseases to human or animals (i.e. Dengue, Leptospirosis, Salmonella)
Directly harm human or animals (i.e bites from bedbugs, cat fleas, hornets)
Create fear or entomophobia to human (i.e. spiders, cockroaches)
Nuisance or their presence or faeces (lizards, flies, pigeons)