The future of bees may depend on understanding their past.

Bees are in trouble, any entomologist will tell you. Honeybee colonies in the United States have suffered devastating losses in recent years. But colony collapse disorder, as it’s called, affects only the species kept in beehives — the European honeybee, Apis mellifera. There are almost 20,000 species of wild bees, and they aren’t faring well, either.

Nearly a third of bumblebee species in the United States are declining. In the Netherlands, more than half of the country’s 357 species of wild bees are endangered. Many species of plants, including crops, depend on wild bees to spread their pollen. When they lose their pollinators, they may suffer, too.

“It’s essential to know what is causing those declines,” said Jeroen Scheper, a graduate student at Alterra, a research institution at Wageningen University in the Netherlands.

But it is not enough to consider the many challenges — from pesticides to parasites — that wild bees face right now. “We need to go back in time,” said Mr. Scheper.