From crochet.about.com - Chart for Manto Butterfly in Filet Crochet
Designed by Sandi Marshall

Working the Chart in Filet Crochet For a 4 dc mesh, beginning chain is 121, plus chain 3, (which will count as first dc of first row), plus chain 2 (which is the ch-2 of the first open mesh) for a total starting chain of 126 chains. Begin by working a double crochet in the 8th chain from the hook. Follow chart for placement of solid mesh and open mesh for each row. For a refresher on how to do open and solid mesh, see Basics link below. Chart is worked starting at the bottom right; work first row right to left. Second row is worked left to right. Continue alternating row directions in this same manner, following chart. Chart is free for your own personal use only. For personal use only indicates that the pattern may be used only for non-commercial use (meaning that you may make items from the pattern for yourself or for gifts but that you may not sell items made from the pattern). Selling is a commercial use, not a personal use.

Adding Antennae: If desired, anntennae may be added after piece is completed. Attach thread at point where you wish one antenna to end. Make number of chains needed to reach to top of head. Slip stitch in a stitch towards the center of the top of the head. Slip stitch over to the point where you want the next antenna to begin. Make same number of chains that you used in first antenna. Attach with slip stitch at the point where you want the antenna to end. End off. Weave in thread ends. See Color Chart at link below if you'd like to see a suggested antennae placement idea. There's no set way to make the antennae - do it whatever way pleases you. Above directions are for straight antennae, but you may wish to make them curved by making a few chains, attach with slip stitch, make a few more chains and attach, repeating this in such a way that the antenna curves ... or you may come up with other ideas.

Basics in How to Do Filet Crochet, here: http://crochet.about.com/library/weekly/aa050298.htm

The Manto Butterfly Chart is an original design created by Sandi Marshall. Pattern copyright 2000 by Sandi Marshall, licensed to About.com, Inc.
Free for your own personal (not for profit) use only. All rights reserved worldwide.
Per copyright law, do not distribute reproduced copies of the chart (with or without charge) in any form. Instead, you are welcome to post the URL of the Manto Butterfly Filet Crochet pattern page so that anyone who would like the chart may come here for themselves and benefit from everything else this site has to offer. Thank you. URL for this printing page is http://crochet.about.com/library/nmanto2.htm
URL of the main page for this pattern is http://crochet.about.com/library/weekly/aa070800.htm
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I also created a color chart version of this butterfly. This link takes you to a page with instructions for crocheting the color chart into an afghan square: http://crochet.about.com/library/weekly/aa062500.htm