ZvZ: Differentiating between early pools, without drone scout, how do I react?

How do I tell the difference between 6/7/8/10 pools and their variants, using only an overlord scout? Both 6 and 10 pool send 6 zerglings across the map, and have no expansion at the normal time. Yet they each require different responses - how do I ensure I choose the correct one?

I'm going 15p/15h/16g, sending the first overlord to his natural, and second overlord (made on 9 supply) along a secondary possible attack path.

Also, how should I modify my build order to counter his build? I'm currently throwing down a spine crawler against all early pools - I don't know if this is optimal though.

Solution 1:

Background info

This is what time their spawning pool will finish based on their build order (in-game time):

6 Pool  ~1:49
7 Pool  ~1:57
8 Pool  ~2:04
9 Pool  ~2:10
10 Pool  ~2:18
11 Pool  ~2:26

Additionally, the build time for a pair of zerglings is 20 seconds, so their zerglings will be on the field at:

6 Pool  ~2:09
7 Pool  ~2:17
8 Pool  ~2:24
9 Pool  ~2:30
10 Pool  ~2:38
11 Pool  ~2:46

Whenever you spot the incoming zerglings (with your scouting overlord), you can make an educated guess on what build order the opponent went for (based on what time it is in the game, and where you've spotted the zerglings on the map).

Scouting

All of that being said I think you should drone scout. Unless you are Master or Grand Master, the potential scouting information you will receive outweighs the lost mining time of your scouting drone. Plus if the other player did go for an early pool, you will have the better economy anyways.

It is good that you are positioning your second overlord along the attack path, and you should be doing this with every overlord in the early part of the game (until they have some sort of anti-air).

Build order & Defending

In ZvZ, a pretty safe build is 14p/14h. Your zergling will spawn later than his, but you usually only have to stall for ~30 seconds. You don't necessarily have to throw down a spine crawler. A spine crawler takes 50 seconds to build, while zerglings only take 20 seconds. When you're defending, don't be afraid to attack with your drones (and if your micro is good, pull back the weak ones), to stall a little until your zerglings are out.

There are a lot of videos on youtube about defending against a 6 pools.

One last thing: while your defending against the zerglings in your base, keep an eye on the minimap! Those overlords you placed along the attack paths earlier are giving you vital information: if you see more zerglings reinforcements coming, keep building more of your own. A lot of players lose when they fail to scout the reinforcements, and try to squeeze in some drones when they should been building more zerglings.