For those that are unaware, Silk Burrowers (aka silkies), are probably parallel kingdom's best kept secret. The reason is that as you kill them they sometimes 'split' and allow the creation of more and more. In this way you can gain more gold, mats, pages and more.
Silkies are found only in asia, so try and find cities that are on that continent. The more secluded the spot, the better the return as you will have to share less. It is a good tactic to put shrines (up to 12) on a silkie spawn. You can also use your war camp, cabins and kd war camps to increase your jump points.
Silkies respawn every 6 hours but can very inconsistent. The best way to ensure a return is to clear out the whole circle. Some spots are very good at respawning. These should be shrined.
Generally you want to get silkies as high as possible in level. Epic / Epic is by far the best yielding around 30 gold per second raw. This means getting your effective level up as high as you can. Effective level is the average of your best weapon and best armor rounded UP. So try and cap something and get to effective level 26.
You'll need a good shield, and maybe even a shield ring. Legion and knight are good with shields. Generally you will unequip your weapon to generate maximum number of spawns which will be just under 200 if you do it right.
You may use a low level honed weapon, but no poison. You may lay into the silkies a bit from time to time with a weapon, especially at the start. In truth it makes little difference.
You may need a few berries to heal but by the end you'll be generating HP back using trodent. You may also want to use a HP ring for that extra 15 HP but it's not really needed. Note that you dont need any BP or armor at all other than your shield.
Try to find 12 spawns then keep cycling them as long as you need gold. Boring but highly effective.
Running the numbers
Epic / Epic will give you roughly 30 gold per second, Epic / Vic roughly 25 and Vic / Vic roughly 20. You get a higher return due to mats (especially with scavenge), and bricks or coins. Good silkie hunting can make you consistently 100k an hour.
Hunter monoliths help a lot, if you have that skill too.
Scavenge is essential, as is trodent. Taunt isnt really that helpful. Hunter's eye is better removed. Dragon master 2 is nice for those extra hitpoints.
Doing this in a group will yield you about 50% more gold but you'll need many more spawns. However warden 3 will help with healing (dont forget to move). If you are legion then you will get a shield bonus too, which is very nice.
Silkies can be hard to find, but once you have enough consistent spawns, can make you 2 million+ gold a day a whole bunch of mats and coins and bricks. I dont know if they will ever be nerfed by perblue but for the moment they are probably the lowest intensity way to make a ton of money in the game. If you employ some of the tips above hopefully it will see you rise up the gold lists! Good luck!