A problem for web-building spiders is how to stop their prey from escaping once it has blundered into the web. Some spiders spin threads that are sticky and so hold it fast. Others spin a tangled mass of finer threads, which has voids in it just the right size to trap insects’ legs (it looks much like the other sort to the naked eye, though rather woolly).
The individual strands are made in the cribellum, an oval plate of chitin with many tiny tubes in it that lies in front of the spinnerets that generate the silk. Spiders of this type are said to be cribellate and the presence of a cribellum is a useful way to group species (those without one are said to be ecribellate).
The origin is the Latin cribrum, “sieve”, which is also the source of cribriform, another adjective used in anatomy and botany, “having numerous small holes; sievelike”, and the obsolete verb percribrate, “to sift; pass through a sieve”. (It’s also thought to be the origin of garble.)