Of the six anniversary shorts, Alien: Specimen was one of two not written by their director, the other one being Alien: Harvest. Kelsey Taylor didn't learn about the project until so close to the submission date that she felt unable to develop a good story herself, so she reached out for ideas from participants who were unable to enter due to living outside the USA. The greenhouse idea was selected out of four proposals pitched to 20th Century Fox and Tongal.
The Facehugger was originally intended to be a practical prop, but the crew couldn't afford an articulated puppet with their limited budget and felt they were unable to get good results with the props they had, so it was achieved with computer-generated visual effects instead to save time.
The original ending featured Julie dying, with her superiors not discovering her body until after the power was restored. The twist that the dog, Maggie, was an android was added late in development as a replacement for this ending when it was decided that Julie should live.