This challenge is part of Fortnite Season 3 Week 10 Challenges and you'll have to collect fireflies in a jar five times. This feature appeared relatively unobtrusively a few weeks ago. Little used in competition, it can be used to set fire to wooden structures.
All you have to do is collect fireflies in your jars: in other words, prepare your flaming ammunition. The challenge clearly states that you must get to the level of the trees in Weeping Woods. There are of course plenty of places in the forest where the fireflies roam after dark.
The map
The main difficulty of this challenge will be to wait until nightfall to collect the fireflies. These insects don't appear during the day. You'll have to camp on the spot, without risking dying, then run to the foot of the trees as soon as night shows the end of its nose.
It's highly recommended that you find a bush and hide in it. This is a very reliable and discreet hideout, easily found in Weeping Woods.
You can easily spot fireflies at the bottom of tall trees because of the glow they create as they fly. Get close to the swarms and collect 'em all!