not a solidbody
The STL translator imports STL files as SolidWorks part documents. You have the option to import STL files as graphical data, solids, or surfaces. When you import STL files as graphical data, you can select the Import texture information check box to import texture information if this data exists.
from the help file
You can set the import options when you import STL or VRML files as SolidWorks documents. The VRML translator supports explicit normals, crease angle smooth shading, and color per vertex, which results in smooth blending of colors.
To set the STL and VRML import options:
Set Files of type to STL (*.stl) or VRML (*.wrl) and click Options.
Select from the options described below, then click OK.
Select a file, then click Open to import the file.
Graphics Body. Imports data as graphical data only. The translator does not attempt to create any features. The graphics icon appears in the FeatureManager design tree with the file type, for example, STL Graphics1.
Solid Body. Attempts to import data as solid bodies. In many cases (especially complex models) some of the data does not knit into a usable solid, in which case the translators import that data as surface bodies. Therefore, in the FeatureManager design tree, you can potentially see a Solid Bodies folder, a Surface Bodies folder, imported solid body features, and imported surface body features.
Surface Body. Imports data as surfaces. The Surface Bodies folder and the imported surface body features appear in the FeatureManager design tree.
Unit. Select the unit of measure for the SolidWorks document. The available units are Millimeters, Centimeters, Meters, Inches, and Feet. The translator does not convert units during import. For example, if the unit of measure of the original document is meters and you import the document with the unit Millimeters, an edge that measures 1 meter in the original document will measure 1 millimeter in the imported document, not 1000 millimeters.
Import texture information (applies only when you select import as Graphics Body). Imports texture information, which if contained in the file, results in a high-quality, realistic-looking image. Choosing to not import texture information may improve performance.
Some possible reasons:
1. SW wont display stl or vrml graphics bodies in dwgs - only surfaces or solids will.
2. If you used surfaces and you cant see it in the dwg view you havent Inserted>Model items>Reference geometry>Surfaces yet.
3. SW will sometimes mysteriously hide the meshes entirely if you move to draft view quality in either wireframe or hidden lines visible/removed display styles -
The display of meshes in dwgs really bogs things down: to avoid processor and graphics card work avoid changing to and among wireframe styles.
Its better to select draft and shaded views when you insert your view and before you place them.