Complex sentence: Since most types of insects have hard exoskeletons that retain their appearance after the insects expire, it is easy and practical to form a collection, and with many thousands of colorful and attractive species known, a collection may become quite large.
Split into simpler sentences: Since most types of insects have hard exoskeletons that retain their appearance after the insects dies, it is easy and practical to form a collection. With many thousands of colorful and attractive species known, a collection may become quite large.