This is an old movie where three men landed on alien planet and found life. Aliens looked like praying mantis. The aliens wrapped them in a cocoon till they wanted to study the humans. They decided to release the men but one wanted to stay and study the aliens. This human had a cold in which the aliens all died and he was trapped there. Anyone know this movie?

I looked up cocoon and could not find movies other than cocoon 1985

So your title asked how to look up movies without titles and I use this site
Action Movies of the 2000's - filmsandtv.com (http://www.filmsandtv.com/genre.php)

Advanced Movie Search at filmsandtv.com (http://www.filmsandtv.com/advsearch.php)