By third instar, Mmp1^unspecified mutant larvae exhibit shortened dorsal trunks with uneven diameter and small constructions; the posterior end of each trunk does not protrude from the animal at the spiracle, but is internalized in the posterior quarter of the body. Additionally, the dorsal trunk is frequently broken somewhere between the posterior and anterior spiracles. Small tracheal tubes sometimes sprout from these breaks. The sizes of Mmp1^unspecified mutant larvae are variable, but they are always smaller than wild-type or heterozygous siblings. Additionally, mutants wander away from their food long before the end of the third instar, much earlier than in wild-type. Embryos resulting from germ-line clones of Mmp1^unspecified display identical phenotypes to animals that are only zygotically mutant for Mmp1^unspecified.