This is not entirely accurate. While it is true that there is a size limit for geckos' ability to stick to walls, this limit is much larger than a human. The largest gecko species, the Tokay gecko, can weigh up to 0.5 kg and has a body length of up to 35 cm. This means that a human would need to be much larger than a Tokay gecko in order to be unable to stick to walls.

In fact, there are several factors that determine an animal's ability to stick to walls, including the size and shape of its feet, the surface roughness of the wall, and the animal's weight. Spiders have a number of adaptations that allow them to stick to walls, including:

* Hairy feet: Spiders' feet are covered in tiny hairs called setae. These setae are incredibly thin and flexible, and they allow spiders to create a strong Van der Waals force with surfaces. Van der Waals forces are weak intermolecular forces that occur between all objects, but they are only significant over very short distances. The setae on spiders' feet are so thin and flexible that they can get very close to surfaces, which allows them to create a strong Van der Waals force.

* Claws: Spiders also have claws on their feet. These claws help them to grip surfaces and prevent them from slipping.

* Lightweight bodies: Spiders are relatively lightweight animals, which means that they don't need to create as much force to stick to walls.

So, while there is a size limit for geckos' ability to stick to walls, this limit is much larger than a human. Spiders are able to stick to walls thanks to a number of adaptations, including their hairy feet, claws, and lightweight bodies.