How do adult fleas obtain blood?

Adult fleas obtain blood by sucking it from their hosts. This process involves the flea using its specialized mouthparts, designed specifically for piercing skin and drawing blood from mammals or birds. When a flea bites, it punctures the skin and creates a small wound, allowing it to access the blood vessels beneath. This feeding behavior is crucial for their survival, as adult fleas require blood for reproduction and sustenance.

The other options do not accurately describe the feeding method of adult fleas. They do not absorb nutrients through the skin, nor do they ingest solid food or consume detritus as a source of nutrition. Instead, their entire feeding mechanism is centered around the blood they extract by sucking, which highlights their adaptation to a parasitic lifestyle.