This post applies only to those <a drachind silkstrander> found in Firiona Vie.
For an idea of their HPs, I randomly killed 10 of these from all over the zone. One on one, strictly melee damage, went as follows:
1 - 1337
2 - 1294
3 - 1384
4 - 1308
5 - 1337
6 - 1278
7 - 1397
8 - 1331
9 - 1292
10 - 1278
So they have on average 1330 HPs, give or take depending upon level and buffs.