Buying slings vs buying sexed female (Smithi & Pulchra)

[TarantulaHomes]

Both pulchra and smithi grow pretty fast until approximately 3-3.5 inches. I got mine in November 2009 and by June/July 2010 both were at 3" leg span. Kept them at room temperature (78-80 degrees), feeding a small cricket every 3-4 days.

Here are their growth records

B. smithi

Acquired Nov 03, 2009. Leg span - 0.65"
12/01/09 - Moult. Leg span - 0.8"
01/15/10 - Moult (45 days). Leg span - 1.1"
02/12/10 - Moult (28 days). Leg span - 1.4"
03/16/10 - Moult (32 days). Leg span - 1.8"
04/24/10 - Moult (39 days). Leg span - 2.3"
06/16/10 - Moult (53 days). Leg span - 3"

G. pulchra

Acquired Nov 03, 2009. Leg span - 0.8"
11/24/09 - Moult. Leg span - 1"
01/30/10 - Moult (67 days). Leg span - 1.3"
02/24/10 - Moult (24 days). Leg span - 1.7"
03/31/10 - Moult (35 days). Leg span - 2"
05/20/10 - Moult (50 days). Leg span - 2.5"
07/10/10 - Moult (51 days). Leg span - 3"