Army ants can move about 20m/h, and move for 15 days at a time before stopping for 20 days to let the pupae hatch. Assuming they move for an average of 12 hours a day, they move ~3600m during their moving phase.
Oulu, Finland to Johannesburg, South Africa (over-land) is about 15,000km, give or take. I picked Oulu because it's about in the middle of Finland, latitude-wise. At 0.24km per day, that's ~62500 days of constant travel or about 171.2 years.
Air is probably faster.
Monarch butterflies famously migrate thousands of km each year. They can move about 50km/hr in still air, and faster with a tailwind, but probably less fast when they're carrying a rock in a big cluster. Assuming they're traveling at quarter-speed, they still move 40x the pace of our army ants, and they can travel in a more direct route - closer to 13,000km.
By this route, traveling the same average of 12 hours a day at 12.5km/h, a swarm of butterflies could easily make the trip in 90 days, probably faster if the butterflies are strong enough to carry the stones alone or in small groups.
Appropriately, butterflies are also often considered symbols of life, hope, and resurrection.
I missed the part earlier where the OP states that the stones are approximately grape-sized. Grapes apparently weigh about 5 grams. A stone of similar size might weigh 10-15 grams, however, butterflies can often carry 40x their own weight or more. This means that a single monarch butterfly weighing 0.5g could feasibly carry a single stone.
The length of the trip, therefore, depends on how fast they can fly while carrying the stones:
Full speed (50km/h): ~3 weeks
Half speed (25km/h): ~6 weeks
I don't think any land or aquatic arthropod will be able to touch that trip time.