The phrase "blood suckers" is a metaphorical term used to describe people or entities that take advantage of others and unfairly drain resources, like money or time, without giving anything in return. Full definition
«God has used President Buhari to seal the mouth of blood suckers who daily cause anguish to Nigerians through the instrumentality of terrorists and insurgents. (nigeriapoliticsonline.com)
Bed bugs have made a (gross) comeback in recent years, with 2015 data from the National Pest Management Association (NPMA) showing nearly all (99.6 %) exterminators had treated the little blood suckers in a 12 - month window. (policygenius.com)
I do however profusely apologize to Leeches and Vampires and other Blood suckers in making a comparison with them to the likes of Mitt Romney. (nystateofpolitics.com)