I have raised a variety of butterflies and this is the first time I have had one that has stayed the same size - maybe 1/2 inch while his fellows have grown to full size. It is an anise swallowtail that I collected from my fennel. It has changed coats afew times and now wears a grown up coat but the other 2 are ready be go into pupae and he is just a tiny guy. Is this just a birth defect?