Guanotelism - Excretion

Arachnids (spiders and scorpions) excrete mostly guanine and hence are said to be guanotelic. Guanine, like uric acid, is relatively non-toxic and insoluble and is excreted in solid form. It is an adaptation to life in arid habitats. It is also a purine and has the same atoms in its ring structure as in uric acid.

In fact, guanine is formed as an intermediate during uric acid synthesis in uricotelic animals. In spiders and scorpions, the inosinic acid pathway terminates in guanine formation. The origin of the four nitrogen atoms of guanine is similar to that of uric acid.