- "A housefly beats its wings 200 times per second. Say "hello, there" out loud. In the time it took you to say that, a fly's wings beat 200 times. A fly moves at about four miles per hour. Which doesn't sound very fast, compared to a falcon hitting almost 200 miles per hour. But trust me, when you're only an eighth of an inch long, four miles an hour is like warp factor nine. And what's really cool is you can do that going down, going left, right, or straight up. And you can change directions in no time. One minute you're shooting straight ahead like a bullet, the next tenth of a second you're going straight up. Cassie was right. It was gross, but it was fun."
The housefly (commonly referred to as just fly) is an aerial bug morph used by the Animorphs.
The housefly was first acquired in The Capture, by Jake, Rachel], Cassie, Marco and Ax. After discovering that the Yeerks have infested an entire hospital staff and are using them to turn patients, as well as their state's governor – who is a Presidential candidate – into Controllers, the Animorphs decide that fly morph would be perfect to infiltrate the hospital. Later in The Warning, Tobias acquires a fly morph.
- "I mean, in some ways it's bad because you can't see very well, so you don't get to look around while you're flying. But nothing flies like a fly. Compared to a fly, any bird is a big, lumbering, clumsy whale. Flies can fly straight up. Straight down. They can turn in less than the blink of an eye. And I'm talking a full, one-hundred-eighty-degree turn in midair, no problem. They can fly on their sides and upside down. They can do loops and figure eights. They can fly figure eights inside a small juice glass. And unlike birds, flies can land on anything. Anything. Horizontal, vertical, rough, smooth, wet, dry, still or moving, living or not. They are very amazing insects. Very gross, very amazing insects."
The housefly is one of the most used bug morphs employed by the Animorphs. It is mainly used for escaping undetected or for infiltration and reconnaissance purposes.
- The Capture (acquired and morphed by Jake, Rachel, Cassie, Marco and Ax; cover morph)
- The Andalite's Gift (morphed by Cassie; partial cover morph)
- The Secret (morphed by Jake)
- The Android (morphed by Jake)
- The Forgotten (North American houseflies; morphed by Jake, Rachel, Cassie, Marco and Ax)
- The Reaction (morphed by Ax, accidentally morphed by Rachel)
- The Unknown (mentioned)
- The Escape (partially morphed by Jake, Rachel, Cassie, Marco and Ax)
- The Warning (acquired by Tobias; morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- The Underground (morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- The Decision (morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- The Departure (mentioned)
- The Discovery (mentioned)
- The Threat (mentioned)
- The Solution (morphed by Rachel and Ax)
- The Pretender (morphed by Jake or Rachel or Cassie)
- The Suspicion (morphed by Cassie and Marco)
- The Extreme (morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- The Attack (morphed by Jake, Rachel, Tobias, Cassie, Marco and Ax)
- The Experiment
- The Separation
- The Illusion
- The Proposal
- The Unexpected
- The Diversion