Do spirits need bodies to manifest?

It mustn't have body to manifest, it did so in front of ancient people, who didn't know anything about spirit, as Paul says : when you were children in faith you were fed with milk, nowI you have teeth to eat. Nowadays people do not need any physical forms to believe in spiritual things.

It is so with angels too, it is believed that they have no wings and no appearance as human beings. They do look like we can imagine them - for they are spiritual beings and can not be visible to us, made of materia. We wouldn't accept their image if we see them as they are indeed.

Do spirits need bodies to manifest?

The short answer is no.

The dreams of St. Joseph, the husband of Mary point that out clearly.

Saint Joseph's dreams

Saint Joseph's dreams are four dreams described in the Gospel of Matthew in the New Testament in which Joseph, the legal father of Jesus, is visited by an angel of the Lord and receives specific instructions and warnings of impending danger. All four dreams come from the period around the Nativity of Jesus and his early life, between the onset of Mary's pregnancy and the family's return from the Flight to Egypt. They are often distinguished by numbers as "Joseph's first dream" and so on. Especially in art history, the first may be referred to as the Annunciation to Joseph.

The four dreams are as follows:

• First dream: In Matthew 1:20-21, Joseph is told not be afraid to take Mary as his wife, because she has conceived by the Holy Spirit. (See also the Annunciation in Luke 1:26-38, when an angel visits Mary and she agrees to conceive "through the power of the Most High".)

• Second dream: In Matthew 2:13, Joseph is warned to leave Bethlehem and flee to Egypt.

• Third dream: In Matthew 2:19-20, while in Egypt, Joseph is told that it is safe to go back to Israel.

• Fourth dream: In Matthew 2:22, because he had been warned in a dream, he departed for the region of Galilee instead of going to Judea.

In art

The dreams have sometimes been depicted in art, though they have never been among the most common subjects from the Life of Jesus in art or the Life of the Virgin. It is often unclear which dream is intended. The second dream is probably most often depicted, and if there is no other indication it can be assumed that is the subject. If the Virgin Mary is present (but no infant Jesus), especially if visibly pregnant or shown spinning, this suggests the first dream, which tends to be shown in an indoor setting. An outside setting may suggest the second dream, as does the angel pointing outside the picture space, urging Joseph to leave. The tools of his carpentry workshop are often shown around him, probably indicating the second dream, although logically there seems to be no reason why these should not be present for the first and third dreams as well. In the absence of a place in a sequence, inscribed text, a title, or decor showing a setting in Egypt, the third and fourth dreams can generally be ruled out where there is uncertainty.

In the Gospel according to St. Matthew it is clear that it was an angel (spirit) that spoke to St. Joseph in a dream.

But after he had considered this, an angel of the Lord appeared to him in a dream and said, “Joseph son of David, do not be afraid to take Mary home as your wife, because what is conceived in her is from the Holy Spirit. She will give birth to a son, and you are to give him the name Jesus, because he will save his people from their sins.” - Matthew 1:20-21

The Dream of Saint Joseph, by Philippe de Champaigne.

Now if the good angels can speak to us in dreams, it makes sense that the demons or evil spirits can do likewise.

Generally speaking spirits have no need the carry one a conversion with the living. Often it is the living who desire such things. Many turn to unhealthy and unsafe practices of the occult and employ such methods as ouija boards which are considered very dangerous spiritually speaking of.

In the Book of Job, Satan manifested his hated against Job by creating storms and plagues over Job, testing him with all sort of evils with God’s permission. Satan did not have a body to demonstrate his hatred of Job!