Using the approximate weights from Question 3, how many spiders would weigh the same as a hamster, a rabbit, and a horse?

Hamster weight $= 100 \text{ g}$
Spider weight $= 1 \text{ g}$
Number of spiders $= \frac{\text{Hamster weight}}{\text{Spider weight}}$

$$= \frac{100 \text{ g}}{1 \text{ g}}$$ $$= 100$$

The number of spiders that weigh the same as one hamster is $\boxed{\text{100}}$.

Rabbit weight $= 2 \text{ kg}$
Convert rabbit weight to grams: $2 \text{ kg} \times 1000 \text{ g/kg} = 2000 \text{ g}$
Spider weight $= 1 \text{ g}$
Number of spiders $= \frac{\text{Rabbit weight}}{\text{Spider weight}}$

$$= \frac{2000 \text{ g}}{1 \text{ g}}$$ $$= 2000$$

The number of spiders that weigh the same as one rabbit is $\boxed{\text{2000}}$.

Horse weight $= 500 \text{ kg}$
Convert horse weight to grams: $500 \text{ kg} \times 1000 \text{ g/kg} = 500000 \text{ g}$
Spider weight $= 1 \text{ g}$
Number of spiders $= \frac{\text{Horse weight}}{\text{Spider weight}}$

$$= \frac{500000 \text{ g}}{1 \text{ g}}$$ $$= 500000$$

The number of spiders that weigh the same as one horse is $\boxed{\text{500000}}$.