When: Cretaceous (~100 million years ago)
What: Melittosphex is a fossil bee. It is the oldest bee fossil ever found, and this tiny tiny (only 3 millimeters long!) specimen, beautifully preserved in amber, can tell us much about the evolution of this amazing group of social insects. The closest relatives to living bees are the wasps, and some wasps are more closely related to bees than they are to other groups of wasps. The crabronid wasps (the digger-wasps) are the wasps most closely related to bees. These wasps are solitary and while the adults feed on nectar, the young larva feed on a spider or insect that mom-wasp procures for them.
Melittosphex is assuredly more closely related to bees than any wasp, with a great deal of anatomical features found only in bees today, such as the morphology of its hindlimbs and the presence of intricately branching hairs on body. Melittosphex also has features reminiscent of its wasp ancestry that are not seen in any living bee species today; specific spurs on its middle pair of legs and a very slender rear most ‘foot’. This combination of features shows that Melittosphex is an excellent example of a transitional fossil, falling between the crabronid wasps and all living species of bees.
Knowledge of Melittosphex and its kin is critically important for determining how the solitary carnivorous (as larva) wasps gave rise to the eusocial herbivorous bees. But that is not all! These ancient bees also help inform us to how the modern plant biota was established. Today’s flora is dominated by angiosperms - the flowering plants, but this is a relatively recent state of things. The earliest known fossils of angiosperms date to only the Jurassic period, and it is not until the early Cretaceous that body fossils are known. It is at about 100 million years ago that the great angiosperm radiation can be seen, and shortly after this the flowering plants begin to dominate. The one specimen of Melittosphex known preserves minute pollen grains between the branching hairs on its body, showing that even 100 million years ago bees were involved in pollination of these flowing plants. It has long been thought that bees and angiosperms evolved in tandem, that each group depends on the other for its success, and little Melittosphex offers more support for this view.