a spiderling

• 681, 297, -48 (seen once)
• -331, 124, -25 (seen once)
• 868, 274, -20 (seen once) (2 of 7 spawns here)
• 767, 514, -49 (seen once)
• -501, 606, -48 (seen once)
• 0, 0, 27161 (seen once) (2 of 24 spawns here)
• -281, -869, -54 (seen once)
• 386, -836, -54 (seen once) (1 of 2 spawns here)
• 273, 326, -45 (seen once)
• -419, 336, -46 (seen once)
• -148, 1439, -54 (seen once)
• -591, 4495, -52 (seen once) (1 of 2 spawns here)
• -582, 32, -32 (seen once)
• 0, 4331, -54 (seen once)
• -487, -846, -54 (seen once)
• -342, -977, -53 (seen once)
• 82, -1081, -53 (seen once)
• 228, 73, -69 (seen once) (1 of 2 spawns here)
• -228, 147, -50 (seen once)
• 294, 102, -83 (seen once)
• 387, 517, -14 (seen once) (1 of 3 spawns here)
• -564, 343, -31 (seen once) (1 of 3 spawns here)
• -117, 3235, -52 (seen once)
• 645, 254, -52 (seen once) (1 of 2 spawns here)
• -36, 588, -52 (seen once)
• 357, 385, -29 (seen once) (1 of 4 spawns here)
• -195, 215, -52 (seen once) (1 of 6 spawns here)
• -292, 550, -52 (seen once) (1 of 6 spawns here)
• -311, 379, -52 (seen once)
• 201, 105, -61 (seen once) (1 of 8 spawns here)

As /loc gives them: Y, X, Z, the most used first; nearby spawns share a spot, and one seen in a single visit may be where the mob had been pulled to.