WHEN YOUR VERY FIRST MEAL IS YOUR SIBLING

Nature never stops amazing us with the incredible diversity of parental strategies that have evolved to increase offspring survival. During development, mothers provide nutrients to their young in different ways, usually through a placenta, maternal tissues, or yolk stored in the egg. But, can you believe that there is an extreme case in which the food that mothers provide is the siblings that are sharing the same maternal space? This phenomenon, known as adelphophagy, is relatively rare in the animal kingdom, but has been documented in vertebrates such as sharks, as well as in invertebrates like echinoderms, insects, molluscs, and annelids.

Maternal feeding of siblings also occurs in two types of invertebrates that are unfamiliar to many of us:  flatworms and ribbon worms. Both are…