Most insertions from large-scale screens have not been characterized for lethality, sterility or other phenotypes when they are first made available. Phenotypes noted here typically reflect the BDSC's assessment of the presence or absence of a balancer when the stock was processed into the collection.

The presence or proportion of balancers in these stocks can change over time, and in balanced lines, the identified insertion might not be responsible for the phenotype. Use caution when attributing function to genes based on insertions even when a lethal or sterile phenotype is classified as "verified". In many cases this means that the phenotype has been associated with the insertion by failure to complement a deficiency for the region of the insertion. In such cases the phenotype could be caused by a closely linked mutation induced by transposition rather than by the identified insertion.