Ladybugs need air, like humans, but unlike humans they do not have lungs. Instead, they take in air through tiny openings in the sides of their abdomen and thorax called spiracles. The distribution of oxygen in ladybugs' bodies also differs from that of a human body, because the oxygen is not carried in the ladybug's blood.
Ladybugs use their spiracles by expanding the muscles in their abdomens. This allows air to rush in through the tiny holes. When the ladybug has enough air, it contracts the muscles in its abdomen and closes the spiracles.
Next, the air is diffused through the ladybug's body. Ladybugs have trachea, small tubes that transport air, just as people do. These trachea are not found in lungs. Instead, the air is absorbed into specialized cells, which are able to transfer it to other cells that need oxygen.
Because of the specialized way that they take in air, ladybugs are able to stay alive in water for a little while by closing their spiracles and slowing their metabolism. However, these insects have not adapted to be able to live underwater for long periods of time.
Many other insects also breathe by using spiracles, just as ladybugs do.