Ok, this is assuming a few points.
1) The Spider-bot is attacking by land (no breaching from underwater).
2) The Spider-bot is making a bee-line for your base/commander.
3) In order to get to your base/commander the Spider-Bot has to go through your defenses.
4) You can see the spider-bot coming
5) It's just a single spider-bot with no back-up
So, what I've noticed with testing is that it's probably a very bad idea to make a horizontal line of ravagers (or other defenses for that matter). Testing shows that one line of six ravagers either stacked on top of each other or in a nice row gets destroyed by the spider, leaving the spider-bot with only around half health after volley .
I find the best turtle is ironically something that resembles an actual turtle shell where proper spacing (I.E AoE from T3 Artillery doesn't affect more then one turret) and a circular defense seems to work best.
Any who, I've come up with what I'd describe as a "Defensive Net"(DN) to catch spider-bots (ironically cos' in nature it's reverse). With the DN I've destroyed the spiderbot, with 5 loses of ravagers with 1 survived.
How to do this is start with a Ravager as an anchor in the middle of your net. Then build two more Ravager's 12 twelve-wall lengths away from your anchor Ravager (use walls as a measuring stick), One Ravager north-east and one Ravager north west. Then build two more Ravagers 12 wall-lengths One south-west and one south-east. Then place the last Ravager beside your anchor/middle Ravager.
If built properly the spider-bot should die in the middle of your DN (read: your territory) leaving at least one last Ravager alive to defend your engineers as you hoof up mass.
Total Mass to build DN: 10,800
Total Energy to build DN: 96,000
Estimated Time to Completion of DN if built from a single T3 Engineer: 6 Ravagers 5:00min 7 Ravagers 6min
Spider Bot Cost:
Total Mass: 19,000
Total Energy: 26,0000
Time to Completion: 8:45min if built from single T3 Engineer
Note: if the spiderbot micros well and I do mean pro-level well, then they can break through the net. Counter, build an extra Ravager beside the anchor Ravager bringing the total up to 7.